A    TEXTBOOK   OF 

ORGANIC  CHEMISTRY* 


The  English  Translation 
from  the  German  of 
A.  BERNTHSEN,  Ph.D. 


EDITED     AND     REVISED    tO     DATE     BY 
J.  J.   SUDBOROUGH,  Ph.D.,  D.Sc.,  F.I.C. 

Professor  of  Organic  Chemistry  in  the  Indian  Institute 
of  Science,  Bangalore 


NEW  YORK 

D.  VAN  NOSTRAND  COMPANY 
EIGHT  WARREN  STREET 


PREFACE 


The  present  edition  is  on  much  the  same  lines  as  the  former, 
but  contains  the  following  new  chapters: — XL VIII.  Fermen- 
tation and  Enzyme  Action ;  XLIX.  Catalytic  Action  of  Finely- 
divided  Metals  and  Metallic  Oxides;  L.  Unsaturation;  LI.  Ali- 
phatic Diazo-  and  Triazo-compounds. 

The  Chapters  on  Alkaloids,  Terpenes  and  Camphors,  and 
Proteins  have  been  rewritten. 

The  earlier  Chapters  give  an  outline  of  General  Systematic 
Organic  Chemistry,  and  the  later  ones  deal  in  somewhat  more 
detail  with  some  of  the  problems  which  have  attracted  a 
considerable  amount  of  attention  within  recent  years. 

Numerous  references  to  original  papers  are  given  in  the 
text,  and  the  following  works  are  recommended  for  special 
study : — 

Meyer  and  Jacobson.     Handbuch  der  organischen  Chemie. 

Lassar-Cohn.     Arbeitsmethoden. 

Th.  Weyl.     Die  Methoden  der  organischen  Chemie. 

Werner.    Lehrbuch  der  Stereochemie. 

Landolt.     Das  optische  Drehungsvermogen. 

0.  Aschan.     Chemie  der  alicydischen  Verbindungen, 

E.  Fischer.     Aminosduren  und  Polypeptide,  1906. 

Do.  Purin  Gruppe,  1907. 

Do.  Kohlenhydrate  und  Fermente,  1909. 

Cain.     The  Diazo-compounds. 

Smiles.    Relations  between  Chemical  Constitution  and  Physical 
Properties. 

iii 


IV  PREFACE 

Stewart.     Stereo-chemistry. 

Do.        Eecent  Advances  in  Organic  Chemistry. 
Sidgwick.     Organic  Chemistry  of  Nitrogen. 
Harden.     Alcoholic  Fermentation. 
E.  F.  Armstrong.     Simple  Carbohydrates  and  Glucosides. 
Bayliss.     Enzyme  Action. 
Schryver.     Proteins. 

Valuable  Summaries  of  certain  fields  of  Organic  Work,  such 
as  Combustion,  Diazo-compounds,  Grignard's  Reagents,  Cam- 
phor, Tautomerism,  Stereo-chemistry  of  Nitrogen,  &c.,  will  be 
found  in  the  Reports  of  the  British  Association  since  1900, 
and  also  in  Ahren's  Sammlung  chemischer  und  chem.-technischer 
Vortmge  from  1897  onwards. 

J.   J.   SUDBOROUGH. 

BANGALORE,  March,  1912. 


ABBEEVIATIONS 


A.  =  Liebig's  Annalen  der  Chemie. 

Abs.  =  Journal  of  the  Chemical  Society.     Abstracts. 
Am.  =  American  Chemical  Journal. 
Annales  —  Annales  de  Chemie  et  de  Physique. 
Arch.  f.  Phys.  =  Archivfur  Physiologic. 

B.  =  Berichte  der  deutschen  Chemischen  Cfesellschaft. 

B.  A.  Rep.  =  British  Association  Report. 

Bull.  Soc.  Chirn.  =  Bulletin  de  la  Socitte  Chimique  a  Paris. 

C.  C.  =  Chemisches  Central-Uatt. 

C.  R.  =  Comptes  rendus  de  I' Academic  des  Sciences. 

J.  A.  C.  S.  =  Journal  of  the  American  Chemical  Society. 

J.  C.  S.  =  Journal  of  the  Chemical  Society.     Transactions. 

J.  Ind.  =  Journal  of  the  Society  of  Chemical  Industry. 

J.  pr.  =  Journal  fur  praktische  Chemie. 

M.  =  Monatshefte  fiir  Chemie  (Wien). 

P.  =  Proceedings  of  the  Chemical  Society. 

Phil.  Mag.  =  Philosophical  Magazine. 

Rec.  =  Recueil  des  Travaux  Chimiques  des  Pays  Bas. 

S.  J.  =  Sudborough  and  James's  Practical  Organic  Chemistry. 

Walker,  Phys.  Chem.  =  James  Walker's  Introduction  to  Physical  Chemistry. 

Zeit.  phys.  =  Zeitschrift  fiir  physikalische  Chemie. 


n  =  normal. 

0-ether  =  Oxygen  ether. 

N-ether  =  Nitrogen  ether. 

B.-pt.  =  Boiling-point. 

M.-pt.  =  Melting-point. 

d  =  dextro. 

I  =  Isevo. 

r  =  racemic. 

«  =  symmetrical. 


i  =  inactive. 
R  =  alkyl  radical. 
Me  =  Methyl,  CH3. 
Et  =  Ethyl,  C2H6. 
Ph  =  Phenyl,  C6H6. 
o  =  ortho. 
m  =  meta. 
p  =  para. 


TABLE  OF  CONTENTS 


INTRODUCTION 

Page 

Qualitative  Analysis         ..».-..-.  2 

Quantitative  Analysis       -  4 

Calculation  of  the  Empirical  Formula       -                  ....  7 

Determination  of  Molecular  Weight                                               -         -  7 

Polymerism  and  Isomerism       -                          12 

Chemical  Theories -        -         -  13 

Explanation  of  Isomerism;   Determination  of  the  Constitution  of 

Organic  Compounds 16 

Rational  Formulae -         -  19 

The  Nature  of  the  Carbon  Atom  19 

Homology        ........         ...        -  20 

Radicals                                               -        - 22 

Classification  of  Hydrocarbons 

Physical  Properties  of  Organic  Compounds                 -         -         -         -  21 

CLASS  I.— ALIPHATIC    OR  OPEN -CHAIN 
COMPOUNDS 

i.  HYDROCARBONS      -        -        . 30 

A.  Saturated  Hydrocarbons,  CnH2n+2 30 

B.  Olefines,  CnH^      -  42 
c.  Acetylene  Series,  CnH2n-2       ...  49 
D.  Hydrocarbons,  CnH2n-6                                      •         *         "  ^3 

ii.  HALOID  SUBSTITUTION  PRODUCTS  OF  THE  HYDROCARBONS     -  54 

A.  Halogen  Derivatives  of  the  Paraffins       -         •         -         -  54 

B.  Halide  Derivatives  of  Unsaturated  Hydrocarbons  -         -  64 

vii 


vili  CONTENTS 

Page 

in.  MONOHYDRIC  ALCOHOLS  OK  ALKYL  HYDROXIDES  65 

A.  Monohydric  Saturated  Alcohols,  CnH2n+1OH           -         -  66 

B.  Monohydric  Unsaturated  Alcohols,  CnH2n_iOH      -         -  81 

C.  Monohydric  Unsaturated  Alcohols,  CnH2n_3OH      -         -  82 

iv.  DERIVATIVES  OF  THE  ALCOHOLS 83 

A.  Ethers  Proper  or  Alkyl  Oxides 83 

B.  Thio-alcohols  and  Thio-ethers 87 

c.  Esters  of  the  Alcohols  with  Inorganic  Acids,  and  their 

Isomers 91 

Esters  of  Nitric  Acid 93 

Derivatives  of  Nitrous  Acid 94 

Esters  of  Sulphuric  Acid 98 

Derivatives  of  Sulphurous  Acid 99 

Alkyl  Derivatives  of  Hydrocyanic  Acid        -         -         -  101 

D.  Amines  or  Nitrogen  Bases  of  the  Alkyl  Radicals    -         -  104 

Hydroxylamines,  Hydrazines        -         -         -         -         -  111 

E.  Alkyl  Derivatives  of  Phosphorus,  Arsenic,  &c.          -         -  113 

F.  Organo -metallic  Compounds 118 

v.  ALDEHYDES  AND  KETONES    -        - 121 

A.  Aldehydes 122 

B.  Ketones 131 

Aldoximes  and  Ketoximes   -         -         -         =         -         -  137 

vi.  MONOBASIC  FATTY  ACIDS 139 

A.  Saturated  Acids,  CnH2nO2                       '-         -        -        -  139 

B.  Unsaturated  Acids,  CnH2n-zO-2                                  -     •    -  161 

C.  Propiolic  Acid  Series,  CnH2n-4O2    -                                     -  166 

D.  Halogen  Substitution  Products  of  the  Monobasic  Acids  -  167 

vii.  ACID  DERIVATIVES        -        -        -        .-**,-        .        -  171 

A.  Esters  of  the  Fatty  Acids       •  ,;.  -r  •  V    r    !     -         -         -  172 

B.  Acid  Chlorides,  Bromides,  &c.         -  /.  ' ,?*  , •--•   '  ••     *         "  178 

C.  Acid  Anhydrides   -         •       ;w  j     •     •;.         .         -         -  180 

D.  Thio-acids  and  Thio-anhydrides      -     .•••».•      *         -         -  181 

E.  Acid  Amides  and  Hydrazides                   -         -                  -  182 

F.  Amido-  and  Imido-chlorides  -  185 

G.  Thiamides  and  Imido-thio-ethers    -                                     -  186 
H.  Amidines  and  Amidoximes    -     .  -c      -;  •       -         -         -  187 


CONTENTS  IX 

Page 

VIII.   POLYHTDRIC  ALCOHOLS-  .£;"«iJ       .'*r    '   ^••'i-.-'n^'  S  .»*»;;•.!/.. ,':  188 

A.  Dihydric  Alcohols  or  Glycols          '.-'       i;  "v^.,/.^.-..!     .  jgg 

B.  Trihydric  Alcohols        •  *•' '' ''.  -  ''•"•''•""       -:<           '  • ''      -  19? 
c.  Tetra-,  Penta-,  and  Hexahydric  Alcohols        •         -         -  201 

ix.  HYDROXY  MONOBASIC  ACIDS  AND  COMPOUNDS  RELATED  TO 

THEM      ...        -      •  ••  '•''•••--'£'•''-'    v^-  r.>':-$  •  •  >.        .  205 

A.  Monohydroxy  Fatty  Acids     -        -       '•'  '"'-'-**"'•         -  205 

B.  Polyhydric  Monobasic  Acids 218 

c.  Hydroxy-aldehydes        -        -        -••>~»n   --4MO-        -  220 

D.  Dialdehydes        '  ij ":  ^/ijs;-)L>    ,    '    ^        -    '    -        -  221 

E.  Diketones      -         -         ......         -         -         -  221 

p.  Aldehydic  Monobasic  Acids 222 

G.  Monobasic  Ketonic  Acids 222 

x.  DIBASIC  ACIDS       -      '  - 231 

A.  Saturated  Dibasic  Acids,  or  Oxalic  Series                 -         -  231 

B.  Unsaturated  Dibasic  Acids 241 

C.  Hydroxy  Dibasic  Acids 247 

D.  Dihydroxy  Dibasic  Acids        ....                  -  249 

Stereo-isomerism  of  the  Tartaric  Acids          -         -         -  250 

E.  Polyhydroxy  Dibasic  Acids    ....                 -  259 
p.  Dibasic  Ketonic  Acids   ..-.-.-  260 

xi.  POLYBASIO  ACIDS 261 

A.  Saturated  and  Unsaturated  Polybasic  Acids  -         -         -  261 

B.  Hydroxy  Polybasic  Acids 262 

xii.  CYANOGEN  COMPOUNDS  -        -        •        -        -        -        -        •  263 

A.  Cyanogen  and  Hydrocyanic  Acid 266 

B.  Halogen  Compounds  of  Cyanogen 272 

C.  Cyanic  and  Cyanuric  Acids    -                                     -  273 

D.  Thiocyanic  Acid  and  its  Derivatives        ....  275 

E.  Cyanamide  and  its  Derivatives        -                                     -  277 

xin.  CARBONIC  ACID  DERIVATIVES                                                    •  279 

A.  Esters    -                                                                                       •  279 

B.  Chlorides        -                             280 


X  CONTENTS 

Page 

C.  Amides,  Ureides,  Purine  Group      -         -         -         -         -  261 

D.  Sulphur  Derivatives  of  Carbonic  Acid     -                  -         -  295 
K.  Amidines  of  Carbonic  Acid     -         .         .                          .  297 

xiv.  CARBOHYDRATES     -                                 298 

A.  Monosaccharoses 300 

B.  Di-  and  Trisaccharoses  -                                                     -  314 

C.  Polysaccharoses -  317 

CLASS  II.— CHEMISTRY  OF  THE  CYCLIC 
COMPOUNDS 

xv.  INTRODUCTION        ...                321 

CARBOCYCLIC  COMPOUNDS 

XVI.   POLYMETHYLENE  DERIVATIVES 322 

xvii.  BENZENE  DERIVATIVES — Introduction 327 

Characteristic  Properties  of  Benzene  Derivatives                  -  328 

Isomeric  Relations 329 

Constitution  of  Benzene 332 

Determination  of  Positions  of  Substituents  -  337 

Occurrence  of  Benzene  Derivatives 340 

Formation  of  Benzene  Derivatives,  &c.                 ...  341 

xvni.  BENZENE  HYDROCARBONS 344 

A.  Homologues  of  Benzene,  CnH2n-6 344 

B.  Unsaturated  Benzene  Hydrocarbons       ....  353 

xix.  HALOGEN  DERIVATIVES  -        •       .       '-        .   "    .        .        -  354 

A.  Additive  Compounds      -        -     —        ....  354 

B.  Substituted  Derivatives  --./--        -         -         -  354 

XX.   NlTRO- SUBSTITUTION    PRODUCTS    OF    THE    AROMATIC    HYDRO- 
CARBONS         -         --     '*'/.-''-'   •'•••      -         -         -  359 

Nitroso-derivatives     ,-         -        1:  :  ;             -•        -        -         -  365 

xxi.  AMINO-DERIVATIVES  OR  ARYLAMINES      -  366 

A.  Primary  Monamines       .        v      '  ..         i         .         .         .  367 

B.  Secondary  Monamines 375 

c.  Tertiary  Monamines 377 


CONTENDS  XI 

Page 

Do  The  Quaternary  Bases    -       ••- '- ' '•='*  ;';  ••-•   •''  * •'•••>  — '  -    -  379 

E.  Diamines,  Triamines,  &c.        -    f'-  ;- -'-  •••'  lT3&fi'iiO   -         -  380 

Acyl  Derivatives  of  Arylamines    -----  381 

Primary  Amines  with  the  Amino-group  in  the  Side  Chain  383 

XXII.   DlAZO-   AND  AZO-COMPOUNDS ;    HYDEAZINES    -     "'•  "'  ' '   ''-~         •  384 

A.  Diazo-compounds  -         -        -;  :  ..-         •        •.,..*.       "  384 

B.  Diazo-amino-compounds        --         :         •        .-        -         -  392 

C.  Azo-compounds  and   Compounds  intermediate   between 

Nitro-  and  Amino-compounds       ._'..'!'.        -        -  394 

D.  Hydrazines    -         -         -        -        -.. '      •  '      -         -         -  397 

E.  Azo-dyes        -        *•                                                    -         -  399 

F.  Phosphorus  Compounds,  &c.;  Organo-metallic  Derivatives  402 

xxiii.  AROMATIC  SULPHONIO  ACIDS-        '-''""'  •'"'    •'' '"' •^•^•'>.}      .  403 

xxiv.  PHENOLS        •        •        •-,-•-                -        -  407 

A.  Monohydric  Phenols       -                                                        -  410 

B.  Dihydric  Phenols  -         .-        --         -         -         -                  -  417 

c.  Trihydric  Phenols  -                                                                 -  419 

xxv.  AROMATIC  ALCOHOLS,  ALDEHYDES,  AND  KETONES  -        -        -  421 

A.  Aromatic  Alcohols      .   - 421 

B.  Aromatic  Aldehydes       -         - 423 

C.  Aromatic  Ketones  -                            ."....  427 

D.  Hydroxy  or  Phenolic  Alcohols,  Aldehydes,  and  Ketones  429 

E.  Quinones 430 

F.  Quinone    Chlorimides,    Quinone    Aniles,    and    Anilino- 

quinones 433 

G.  Pseudo-phenols.     Methylene-quinones    -  434 

xxvi.  AROMATIC  ACIDS 435 

A.  Monobasic  Aromatic  Acids 442 

1.  Monobasic  Saturated  Acids 444 

2.  Monobasic  Unsaturated  Acids          -         -        -         -  454 

3.  Saturated  Phenolic  Acids 456 

4.  Alcohol-  and  Keto-acids 461 

5.  Unsaturated  Monobasic  Phenolic  Acids  -         -         -  463 

B.  Dibasic  Acids         ...-.---  464 
c.  Polybasic  Acids -  470 


v  PREFACE 

Stewart.    Stereo-chemistry. 

Do.        Recent  Advances  in  Organic  Chemistry. 
Sidgwick.     Organic  Chemistry  of  Nitrogen. 
Harden.     Alcoholic  Fermentation. 
E.  F.  Armstrong.     Simple  Carbohydrates  and  Glucosides. 
Bayliss.     Enzyme  Action. 
Schryver.     Proteins. 

Valuable  Summaries  of  certain  fields  of  Organic  Work,  such 
as  Combustion,  Diazo-compounds,  Grignard's  Eeagents,  Cam- 
phor, Tautomerism,  Stereo-chemistry  of  Nitrogen,  &c.,  will  be 
found  in  the  Reports  of  the  British  Association  since  1900, 
and  also  in  Ahren's  Sammlung  chemischer  und  chem.-technischer 
Vortmge  from  1897  onwards. 

J.  J,  SUDBOROUGH. 

BANGALOKE,  March,  1912. 


ABBEEVIATIONS 


A.  =  Liebig's  Annalen  der  Chemie. 

Abs.  =  Journal  of  the  Chemical  Society.     Abstracts. 
Am.  =  American  Chemical  Journal. 
Annales  =  Annales  de  Chemie  et  de  Physique. 
Arch.  f.  Phys.  =  Archiv  filr  Physiologic. 

B.  =  Berichte  der  deutschen  Chemischen  Cfesellschaft. 

B.  A.  Rep.  =  British  Association  Report. 

Bull.  Soc.  China.  =  Bulletin  de  la  Socie'te'  Chimique  a  Paris. 

C.  C.  =  Chemisches  Central-Uatt. 

C.  R.  =  Comptes  rendus  de  VAcaddmie  des  Sciences. 

J.  A.  C.  S.  =  Journal  of  the  American  Chemical  Society. 

J.  C.  S.  =  Journal  of  the  Chemical  Society.     Transactions. 

J.  Ind.  =  Journal  of  the  Society  of  Chemical  Industry. 

J.  pr.  =  Journal  filr  pralctische  Chemie. 

M.  =  Monatshefte  fur  Chemie  (Wien). 

P.  =  Proceedings  of  the  Chemical  Society. 

Phil.  Mag.  =  Philosophical  Magazine. 

Rec.  =  Recueil  des  Travaux  Chimiques  des  Pays  Bas. 

S.  J.  =  Sudborough  and  James's  Practical  Organic  Chemistry. 

Walker,  Phys.  Chem.  =  James  Walker's  Introduction  to  Physical  Chemistry. 

Zeit.  phys.  =  Zeitschrift  fur  physikalische  Chemie. 


n  =  normal. 

0-ether  =  Oxygen  ether. 

N-ether  =  Nitrogen  ether. 

B.-pt.  =  Boiling-point. 

M.-pt.  =  Melting-point. 

d  —  dextro. 

I  =  Isevo. 

r  =  racemic. 

«  =  symmetrical. 


i  —  inactive. 
R  =  alkyl  radical. 
Me  =  Methyl,  CH3. 
Et  =  Ethyl,  C2H6. 
Ph  =  Phenyl,  C6H6. 
o  =  ortho. 
m,  =  meta. 
p  =  para. 


TABLE  OF  CONTENTS 


INTRODUCTION 

Page 

Qualitative  Analysis         -                                 ,  «..            ;..^r  2 

Quantitative  Analysis      •     : ,  -  4 

Calculation  of  the  Empirical  Formula     ir.-...i           -,..r-    /,,*A     •        •  7 

Determination  of  Molecular  Weight                                               -         -  7 

Polymerism  and  Isomerism    '   -                        <-.if*  r,  "'O^rfTf      "         *  12 

Chemical  Theories   -    .  ,.?/    ,,j   .;,,.- ,  ;.  i  » ,.'..,.  ^ ,..  ;  -•  13 
Explanation  of  Isomerism;   Determination  of  the  Constitution  of 

Organic  Compounds 16 

Rational  Formulae 19 

The  Nature  of  the  Carbon  Atom  19 

Homology 20 

Radicals                                               22 

Classification  of  Hydrocarbons 23 

Physical  Properties  of  Organic  Compounds        -        -        -        -        -21 

CLASS  I.— ALIPHATIC    OR  OPEN -CHAIN 
COMPOUNDS 

i.  HYDROCARBONS     -        - 30 

A.  Saturated  Hydrocarbons,  CnH^+a 30 

B.  Olefines,  CnH2n      -  42 
c.  Acetylene  Series,  CnH2n-2                                                   -  49 
D.  Hydrocarbons,  CnH2n_6                                                         -  53 

ii.  HALOID  SUBSTITUTION  PRODUCTS  OF  THE  HYDROCARBONS     -  54 

A.  Halogen  Derivatives  of  the  Paraffins       -         •         -  54 

B.  Halide  Derivatives  of  Unsaturated  Hydrocarbons  -         -  64 

vii 


Vlll  CONTENTS 

Page 
in.  MONOHYDEIC  ALCOHOLS  OK  ALKYL  HYDROXIDES  65 

A.  Monohydric  Saturated  Alcohols,  CnH2n+iOH  -         -       66 

B.  Monohydric  Unsaturated  Alcohols,  CnH2n_iOH      -         -       81 
0.  Monohydric  Unsaturated  Alcohols,  CnH^.sOH      -         -       82 


iv.  DERIVATIVES  OF  THE  ALCOHOLS    ......  83 

A.  Ethers  Proper  or  Alkyl  Oxides       .....  83 

B.  Thio-alcohols  and  Thio-ethers          .....  87 
c.  Esters  of  the  Alcohols  with  Inorganic  Acids,  and  their 

Isomers    .........  91 

Esters  of  Nitric  Acid  .......  93 

Derivatives  of  Nitrous  Acid          .....  94 

Esters  of  Sulphuric  Acid      ......  98 

Derivatives  of  Sulphurous  Acid    .....  99 

Alkyl  Derivatives  of  Hydrocyanic  Acid        -         -         -  101 

D.  Amines  or  Nitrogen  Bases  of  the  Alkyl  Kadicals    -         -  104 

Hydroxylamines,  Hydrazines        .....  Ill 

E.  Alkyl  Derivatives  of  Phosphorus,  Arsenic,  &c.          -         -  113 

F.  Organo-metallic  Compounds  ......  118 

v.  ALDEHYDES  AND  KETONES    -        -        .....  121 

A.  Aldehydes     .........  122 

B.  Ketones         .........  131 

Aldoximes  and  Ketoximes  -         -         -        -        -         -  137 

vi.  MONOBASIC  FATTY  ACIDS      .......  139 

A.  Saturated  Acids,  CnH2nO2                        •        -        -        -  139 

B.  Unsaturated  Acids,  CnH2n_2O2                                        .   -  161 

C.  Propiolic  Acid  Series,  CnH2n_4O2   -  A,    *I  1   *.:                -  166 

D.  Halogen  Substitution  Products  of  the  Monobasic  Acids  -  167 

vn.  ACID  DERIVATIVES        .....        •        .        -171 

A.  Esters  of  the  Fatty  Acids       -         fr/JI-i         -'       -         -  172 

B.  Acid  Chlorides,  Bromides,  &c.         -.'•>.;'*  &  •*  •'-,     -         -  178 

C.  Acid  Anhydrides    .....  .;  •  '  *     .    -         -  180 

D.  Thio-acids  and  Thio-anhydrjdes      -         »      .-.-         •         -  181 

E.  Acid  Amides  and  Hydrazides          -         -         -         -         -  182 

F.  Amido-  and  Imido-chlorides  -  185 

G.  Thiamides  and  Imido-thio-ethris                                         -  186 
H.  Amidines  and  Amidoximes    -                                  ••_--••      -  187 


CONTENTS  IX 

Page 

viii.  POLYHYDRIC  ALCOHOLS-       ^  -.qh^'i "  .»••  .-?v;r>jtfir. .;.»..,    ,  iss 

A.  Dihydric  Alcohols  or  Glycols                                 r  -. :      .  188 

B.  Trihydric  Alcohols         -         -       -V        -    '           •' -  ;s     -  197 
c.  Tetra-,  Penta-,  and  Hexahydric  Alcohols        -        -         •  201 

ix.  HYDROXY  MONOBASIC  ACIDS  AND  COMPOUNDS  RELATED  TO 

THEM      -        -        -        -   -     -' :'''; "'-*" '"'^ri^  r<"4  •  ••'•   .        .  205 

A.  Monohydroxy  Fatty  Acids     -         -         -„'-*'-.•'     .  205 

B.  Polyhydric  Monobasic  Acids  -         -         -         -         -         -  218 

c.  Hydroxy-aldehydes        -  ;'  -~':'*  • '  ^  v  ->1  ;   -.«*i'.   -         -  220 

D.  Dialdehydes         '  1! ':   '.    s    -:J: '    .    •     .         .         -         -  221 

E.  Diketones      -         -         -         -         *..    *  r^rnj.^ivy   •  221 

F.  Aldehydic  Monobasic  Acids 222 

G.  Monobasic  Ketonic  Acids       -  '  '  *£r'a*t$        ...  222 

x.  DIBASIC  ACIDS      -        -        -        -       -       -       -   .    -        -  231 

A.  Saturated  Dibasic  Acids,  or  Oxalic  Series                 -         -  231 

B.  Unsaturated  Dibasic  Acids 241 

C.  Hydroxy  Dibasic  Acids 247 

D.  Dihydroxy  Dibasic  Acids        ....                  .  249 

Stereo-isomerism  of  the  Tartaric  Acids          -         -         -  250 

E.  Polyhydroxy  Dibasic  Acids    ....                 -  259 

F.  Dibasic  Ketonic  Acids 260 

xi.  POLYBASIG  ACIDS 261 

A.  Saturated  and  Unsaturated  Polybasic  Acids  -         -         -  261 

B.  Hydroxy  Polybasic  Acids 262 

xn.  CYANOGEN  COMPOUNDS  -....---  263 

A.  Cyanogen  and  Hydrocyanic  Acid 266 

B.  Halogen  Compounds  of  Cyanogen  -                  ...  272 

C.  Cyanic  and  Cyanuric  Acids    ...                  -  273 

D.  Thiocyanic  Acid  and  its  Derivatives       ....  275 

E.  Cyanamide  and  its  Derivatives        ...                  .  277 

xin.  CARBONIC  ACID  DERIVATIVES                                                    •  279 

A.  Esters    -                                                                                    •  279 

B.  Chlorides 280 


X  CONTENDS 

Page 

c.  Amides,  Ureides,  Purine  Group      -        -         -         -         -  261 

D.  Sulphur  Derivatives  of  Carbonic  Acid     -  •  295 

E.  Amidines  of  Carbonic  Acid     -         -         -         -  -  297 

xiv.  CARBOHYDRATES     -  298 

A.  Monosaccharoses 300 

B.  Di-  and  Trisaccharoses  -         -         -         -  -         -  314 

c.  Polysaccharoses •  317 

CLASS  II.— CHEMISTRY  OF  THE  CYCLIC 
COMPOUNDS 

xv.  INTRODUCTION        ...  321 

CAEBOCYCLIC  COMPOUNDS 

XVI.   POLYMETHTLENE   DERIVATIVES  ....  -  322 

xvii.  BENZENE  DERIVATIVES — Introduction     .....  327 

Characteristic  Properties  of  Benzene  Derivatives  -  328 

Isomeric  Relations 329 

Constitution  of  Benzene      ....  .  332 

Determination  of  Positions  of  Substituents  -  337 

Occurrence  of  Benzene  Derivatives 340 

Formation  of  Benzene  Derivatives,  &c.  -         -         -  341 

xviii.  BENZENE  HYDROCARBONS 344 

A.  Homologues  of  Benzene,  Cnil2n-6 344 

B.  Unsaturated  Benzene  Hydrocarbons       ....  353 

xix.  HALOGEN  DERIVATIVES  ...  ....  354 

A.  Additive  Compounds 354 

B.  Substituted  Derivatives  -'..--        -         .         -  354 

XX.   NlTRO- SUBSTITUTION    PRODUCTS    OF    THE    AROMATIC    HYDRO- 
CARBONS ...         .  .      ,./       ...         .         .  359 

Nitroso-derivatives     -         -         -  -         -         -         -  365 

xxi.  AMINO-DERIVATIVES  OR  ARYLAMINES      -  366 

A.  Primary  Monamines       •         «         *  <.-         .  367 

B.  Secondary  Monamines    -         -         -.       -         -         -         -375 
c.  Tertiary  Monamines       -        -        -        r    .    -V      -        -  377 


CONTENDS  XI 

Page 

Do  The  Quaternary  Bases    -       —  :"' '•••:-  '•  '•  '-^:^~i •••«>.;-.'?  -    -  379 

E.  Diamines,  Triamines,  &c.        -    :; '.  -  ;  ^   -j ;-..». ;i<':  .         .  350 

Acyl  Derivatives  of  Arylamines   -         -         -         -         -  381 

Primary  Amines  with  the  Amino-group  in  the  Side  Chain  383 

XXII.   DlAZO-   AND  AZO-COMPOUNDS ;    HTDEAZINES    -       '    •  ';  "-L         •  384 

A.  Diazo-compounds  -         -      ,,•    ,._,•..._...-        •        -,.      -  384 

B.  Diazo-amino-compounds        ^     .   7        r        -        -         -  392 
c.  Azo-compounds  and   Compounds   intermediate   between 

Nitro-  and  Amino-compounds       -     .    -  ',    -        -        -  394 

D.  Hydrazines    -         -         -        -        -_       -      ' ''<.',       -        -  397 

E.  Azo-dyes        -         -       -        ...        *^       -        -  399 

F.  Phosphorus  Compounds,  &c.;  Organo -metallic  Derivatives  402 

xxm.  AROMATIC  SULPHONIO  ACIDS-        ''•'""  •  '"'• ''' " ;"- :''* '''•  •       •  403 

xxiv.  PHENOLS        ..-•....                .  407 

A.  Monohydric  Phenols       -         .Jl*  •*'„*'                       .         .  410 

B.  Dihydric  Phenols  -         -         - :'        -         -         -                  -  417 
c.  Trihydric  Phenols  -                                                                 -  419 

xxv.  AROMATIC  ALCOHOLS,  ALDEHYDES,  AND  KETONES  -        -        -  421 

A.  Aromatic  Alcohols 421 

B.  Aromatic  Aldehydes 423 

c.  Aromatic  Ketones  -         -                  :""''*         •         •         -  427 

D.  Hydroxy  or  Phenolic  Alcohols,  Aldehydes,  and  Ketones  429 

E.  Quinones 430 

P.  Quinone    Chlorimides,    Quinone    Aniles,    and    Anilino- 

quinones 433 

G.  Pseudo-phenols.     Methylene-quinones    -  434 

xxvi.  AROMATIC  ACIDS 435 

A.  Monobasic  Aromatic  Acids 442 

1.  Monobasic  Saturated  Acids 444 

2.  Monobasic  Unsaturated  Acida          -         -        -         -  454 

3.  Saturated  Phenolic  Acids         -  456 

4.  Alcohol-  and  Keto-acids  -                            -         -         -  461 

5.  Unsaturated  Monobasic  Phenolic  Acids   -         -         -  463 

B.  Dibasic  Acids         ...---..  464 
c.  Polybasic  Acids •         -  470 


xii  CONTENTS 

Page 
xxvu.  COMPOUNDS  CONTAINING  TWO  OR  MORE  BENZENE  NUCLEI; 

DIPHENYL  GROUP -  470 

XXVIII.  DlPHENYL-METHANE  GROUP 474 

XXIX.  DlBENZYL  GROUP 477 

xxx.  TRIPHENYL-METHANE  GROUP  480 

Triphenyl-methane  Dyes  482 

1.  Amino-  and  Diamino-triphenyl-methane  Group  483 

2.  Rosaniline  Group 484 

3.  Aurine  Group  490 

4.  Eosin  Group   -  491 

xxxi.  COMPOUNDS  WITH  CONDENSED  BENZENE  NUCLEI-        -  494 

Naphthalene  Group 494 

xxxn.  ANTHRACENE  AND  PHENANTHRENE  GROUPS-        -                 •  504 

A.  Anthracene 504 

B.  Phenanthrene 510 

C.  Complex  Hydrocarbons 512 

HETEROCYCLIC  COMPOUNDS 

xxxm.  INTRODUCTION     -        -     "•        -        -        -        -                -  513 

xxxiv.  FURANE  GROUP  ...                                                  -  515 

xxxv.  COMPOUNDS  FORMED  BY  THE  CONDENSATION  OF  A  BENZENE 
NUCLEUS  WITH  A  FURANE,  THIOPHENE,  OR  PYRROLE 

RING-        -    ;-,  r»-v'Oi>M';:K.      *        •        •        "        •  52° 

Indole  Group -  521 

Indigo  and  Related  Compounds       -                                     -  525 

xxxvi.  PYRAZOLE  GROUP        -        -      •«»••/••  •«'•-.  -•    ••':  -...  528 

A.  Pyrazole  Group  -         .;;-.;"  J                                     -  528 

B.  Thiazole  Group  -  529 

XXXVII.    SlX-MEMBERED   HETEROCYCLIC  RlNGS    -  530 

A.  Pyrones      -----  531 

B.  Pyridine     -         -         -         -         -.       •    .,  r.  "•    •;         -  533 


CONTENTS  Xiii 

Page 

XXXVIII.   QUINOLINE  AND  AOBIDINE  GROUPS      -                                             •  *41 

A.  Quinoline  Group  541 

1.  Chromone  Group                                                       -  541 

2.  Quinoline  and  its  Derivatives       -                           •  542 

3.  Iso-quinoline        -         -                         T^    ,  ,;;  .     .  547 

B.  The  Acridine  Group  -        -     •    •       ^  i      *  '>  X       .  547 

XXXIX.   SlX-MKMBEEED  HETEROCYCLIO  COMPOUNDS  WITH  POUK  CAB- 
BON  ATOMS  IN  RING  -                                                   -  549 
The  Diasines  -        -        .        .        .                                   .  550 
Phenoxazines  and  Phenthiazines     -    '     »'"       •       '  -1 "      -  554 

XL,  ALKALOIDS        .....                                 .  554 

A,  Alkaloids  related  to  Pyridine      -       "V  557 

B.  Bases  derived  from  Quinoline     -                                   •  558 
c.  Bases  derived  from  Iso-quinoline          -                  -         -  560 

D.  The  Morphine  Group  -                                                       -  564 

E.  Strychnine  Bases                                                              •  565 

F.  Solanine  Bases   -                                  ....  565 

XLL  TERPENES  AND  CAMPHORS-        ......  567 

A.  Open  Chain  Olefinic  Terpenes  and  Camphors  568 

BO  Monocyclic  Terpenes  and  Camphors    •  572 
o.  Complex  Cyclic  Terpenes  and  Camphors      •         -         .581 

D.  Compounds  related  to  Terpenes  -        -        -  589 

XLII.  RESINS;  GLUCOSIDES  591 

A.  Resins        ......  591 

B.  Glucosides-        ....        *  =592 

XLIII.  ALBUMINS;  PHYSIOLOGICAL  CHEMISTRY     -  593 

xxiv.  REDUCTION 601 

A.  Nascent  Hydrogen     .......  601 

B.  Other  Chemical  Methods    -         -         -        -        -        -609 

C.  Catalytic  Reduction •  610 

D.  Electrolytic  Reduction        -         •         •         *        -         -  614 


XIV  CONTENTS 

Page 

XLV.  OXIDATION        ...                *   .    *       »       »  616 

A.  Permanganate    -  618 

B.  Chromic  Acid  Derivatives  -  620 
c.  Nitric  Acid         -                          »•>•>•-  621 
D.  Sulphuric  Acid  -                  ......  622 

B.  Peroxides ......  622 

r.  Oxygen  and  Ozone      •  623 

G.  Other  Oxidizing  Agents                                                   •  625 

H.  Electrolytic  Oxidation        -                                            -  626 

XLVI.  STEREOCHEMISTRY  OF  SULPHUR,  SELENION,  TIN,  AND  NITRO- 
GEN COMPOUNDS-        -        -                                        -  627 

A.  Sulphur  Compounds  -  628 

B.  Selenion  Compounds                                                        -  628 
o.  Tin  Compounds                                                       -         -  629 

D.  Silicon  Compounds     ....                           .  629 

E.  Nitrogen  Compounds           ......  631 

p.  Phosphorus  Compounds       -         -         -         -  634 

G.  Cobalt  Compounds 634 

H.  Carbon  Compounds,  with  Semicyclic  Double  Linkings  63$ 

XLVH.  RELATIONSHIPS   BETWEEN   PHYSICAL   PROPERTIES   AND 

CHEMICAL  CONSTITUTION     -                                         .  635 

A.  Boiling-point      -'-"''..  635 

B.  Melting-point     ---..«-..  638 

0.  Molecular  Volume      -   '  '  "J-    "'"-  4      -                          -  639 

D.  Molecular  Refraction                                                       -  641 

E.  Molecular  Magnetic  Rotation      -      "  -        •        -         •  644 
p.  Absorption  Spectra     -        -         -        .-'."-.        .  647 
G.  Anomalous  Electric  Absorption  -                 .    -   .        .  655 
H.  Optical  Activity -656 

Asymmetric  Synthesis      -         -         -        ....  660 

The  Walden  Inversion     -        •        •                 -  661 

1.  Electrical  Conductivity        •        •     "  -       •-"--.        -663 

XLVIIL  FEBMENTATION  AND  ENZYME  ACTION     a:  »C- •>*:.     -        -  666 

A.  Alcoholic  Fermentation      -        -        .    i  .V    ;  .        .  666 

B.  Enzyme  Action •        •      .  •  671 


CONTENTS  XV 

Page 
XLIX.  CATALYTIC    ACTION    OP    FINELY -DIVIDED    METALS   AND 

METALLIC  OXIDES       -        -  674 

Oxidations  674 

Dehydration  ...                                            -  674 

Esterification  -        >         -         -  677 

Formation  of  Amines,  Thiols,  Ketones     ....  677 

L.  UNSATURATION 678 

A.  Types  of  Unsaturation 678 

B.  Properties  of  Unsaturated  Acids  as  affected  by  the 

position  of  the  Double  Bond 679 

c.  Compounds  with  Conjugate  Double  Bonds  -         -        -  681 

D.  Compounds  of  Di-  and  Trivalent  Carbon           -  -         -  683 

Carbon  Monoxide     -         -         -'       -                  -         -  683 

Carbylamines  -         -         -         -         •         -         -         -  684 

Metallic  Cyanides    -        -        •        -        -        -        -  684 

Keactions    of    Metallic    Cyanides.      Formation    of 

Nitriles  and  Carbylamines   -                           -  685 

FulminicAcid          .......  687 

Tervalent  Carbon :  Triphenyl-methyl        -        -        -  690 

E.  Ketens -  691 

P.  Unsaturation  and  Physical  Properties          -         •         •  693 

LL  ALIPHATIC  DIAZO-  AND  TRIAZO-COMPOUNDS       -        •        •  694 

A.  Diazo-compounds        .......  694 

B.  Triazo-compounds      •        • 695 

INDEX            ......        .        *        .        •  697 


ORGANIC  CHEMISTRY 


INTRODUCTION 

Organic  Chemistry  is  the  Chemistry  of  the  Carbon  Com- 
pounds. Formerly  those  compounds  which  occur  in  the 
animal  and  vegetable  worlds  were  classed  under  Organic,  and 
those  which  occur  in  the  mineral  world  under  Inorganic 
Chemistry,  the  first  to  adopt  this  arrangement  having  been 
Ltmfoy  in  his  Cours  de  Chimie  (1675).  After  the  recognition 
of  the  fact  that  all  organic  substances  contain  carbon,  it  was 
thought  that  the  difference  between  organic  and  inorganic 
compounds  could  be  explained  by  saying  that  the  latter  were 
capable  of  preparation  in  the  laboratory,  but  the  former  only 
in  the  organism,  under  the  influence  of  a  particular  force,  the 
life  force — vis  vitalis — (Berzelius).  But  this  assumption  was 
rendered  untenable  when  Wohler  in  1828  synthetically  pre- 
pared urea,  CON2H4,  a  typical  secretion  of  the  animal 
organism,  from  cyanic  acid  and  ammonia,  two  compounds 
which  were  at  that  time  held  to  be  inorganic;  and  when, 
shortly  afterwards,  the  synthesis  of  acetic  acid,  by  the  use  of 
carbon,  sulphur,  chlorine,  water,  and  zinc,  was  effected. 

Since  then  so  many  syntheses  of  this  kind  have  been  achieved 
as  to  prove  beyond  doubt  that  the  same  chemical  forces  act 
both  in  the  organic  and  inorganic  worlds. 

The  separation  of  the  two  branches,  Organic  and  Inorganic 
Chemistry,  from  each  other  is,  however,  still  retained  for  con- 
venience sake,  although  the  original  reasons  for  this  separation, 
which  at  the  time  was  more  or  less  a  matter  of  necessity,  have 
since  been  found  to  be  erroneous.  In  consequence  of  the  great 
capacity  of  combining  with  one  another  which  carbon  atoms 
possess,  the  number  of  organic  compounds  is  extraordinarily 
large,  and  in  order  to  be  in  a  position  to  study  them,  it  is 
necessary  to  have  a  knowledge  of  the  other  elements,  including 

(B480)  1  A 


this  htetal?.:  -This  'garbojx  compounds,  many  of  the  most  im- 
portant bf  which  €©ntaink  only  carbon  and  hydrogen,  or  carbon, 
hydrogen,  and  oxygen,  also  stand  in  a  closer  relationship  to 
each  other  than  do  the  compounds  of  the  other  elements. 
Partly  upon  grounds  of  convenience,  carbon  itself  and  some 
of  its  principal  compounds,  such  as  carbonic  acid,  which  is 
so  widely  distributed  in  the  mineral  kingdom,  are  treated  of 
under  Inorganic  Chemistry. 

The  expressions  "organic"  and  "organized"  substances 
should  not  be  confused;  organized  substances,  e.g.  leaves, 
nerves  and  muscles,  and  also  the  life-processes  which  go  on 
in  the  interior  of  the  organism,  are  treated  of  under  Physiology 
and  Physiological  Chemistry. 

Constituents  of  the  Carbon  Compounds 

Many  organic  substances  are  composed  of  carbon  and  hydro- 
gen only,  and  are  then  termed  hydrocarbons,  for  instance, 
ethylene,  benzene,  petroleum,  naphthalene,  and  oil  of  turpen- 
tine; a  vast  number  consist  of  carbon,  hydrogen,  and  oxygen, 
for  instance,  wood  spirit,  alcohol,  glycerine,  aldehyde,  oil  of 
bitter  almonds,  formic  acid,  acetic  acid,  stearic  acid,  tartaric 
acid,  benzoic  acid,  carbolic  acid,  tannic  acid,  and  alizarin; 
many  compounds  contain  carbon,  hydrogen,  and  nitrogen, 
for  instance,  prussic  acid,  aniline,  and  coniine;  as  examples 
of  compounds  containing  carbon,  hydrogen,  nitrogen,  and 
oxygen,  may  be  taken  urea,  uric  acid,  indigo,  morphine,  and 
quinine.  In  addition  to  these,  sulphur,  chlorine,  bromine, 
iodine,  phosphorus,  and,  generally  speaking,  the  larger  number 
of  the  more  important  elements,  are  also  frequent  constituents 
of  the  carbon  compounds. 

Qualitative  Analysis  of  Organic  Compounds 

The  presence  of  Carbon  in  a  compound  is  often  proved  by 
the  "carbonization"  of  the  latter,  e.g.  starch,  sugar,  &c.,  when 
heated  in  a  glass  tube,  or  when  warmed  with  concentrated 
sulphuric  acid.  Carbon  compounds  which  readily  volatilize, 
e.g.  alcohol,  chloroform,  acetic  acid,  do  not  give  these  tests, 
but  many  of  them  deposit  carbon  when  their  vapours  are  led 
through  a  red-hot  tube.  The  best  proof  of  the  presence  of 
carbon  is  obtained  by  completely  oxidizing  the  organic  com- 
pound by  either  heating  it  with  copper  oxide  (see  below),  or 


QUALITATIVE  ANALYSIS  3 

by  leading  its  vapour  over  the  glowing  oxide.  The  carbon 
present  is  thus  converted  into  carbon  dioxide,  and  the  Hydro- 
gen into  water. 

Nitrogen  in  organic  compounds  is  recognized — 

(a)  Frequently  by  a  smell  resembling  that  of  burnt  hair, 
upon  heating; 

(b)  Frequently  by  the  presence  of  red  fumes,  or  by  explosion, 
upon  heating  (nitro-  and  diazo-compounds); 

(c)  In  many  cases  by  the  liberation  of  ammonia  upon  heating 
with  soda-lime  (Wohler)-, 

(d)  In  all  cases  by  heating  with  potassium  (and  in  most 
cases  with  sodium),  and  testing  the  metallic  cyanide  formed 
— (see  Cyanogen  Compounds) — by  dissolving  the  fused  mass 
in  water,  adding  a  few  drops  of  ferrous  sulphate  solution, 
boiling,  and  acidifying  with  hydrochloric  acid  (formation  of 
Prussian  Blue) ;  or  by  converting  the  cyanide  into  thiocyanate, 
and  proving  the  presence  of  the  latter  by  means  of  the  blood- 
red  coloration  with  ferric  chloride.     [See  tests  for  hydrocyanic 
acid  (Lassaigne).]     If  sulphur  be  likewise  present,  iron  filings 
must  be  added. 

Testing  for  the  Halogens.  Direct  precipitation  by  nitrate 
of  silver  is  usually  not  practicable;  thus,  no  chlorine  can  bo 
detected  in  chloroform  even  upon  boiling  it  with  AgN03. 
The  halogens  are  therefore  tested  for: 

(a)  By  heating  the  substance  on  a  platinum  wire  with  cupric 
oxide  in  the  Bunsen  flame,  or  by  causing  the  vapour  of  the 
compound  to  pass  over  glowing  copper  gauze;   in  this  way 
chlorine  gives  first  a  blue  and  then  a  green  flame  coloration, 
and  iodine  a  green  (Beilsteiri) ; 

(b)  By  heating  the  substance  strongly  with  pure  lime,  and 
testing  the  solution  of  the  naloid  calcium  salt  produced  with 
silver  nitrate; 

(c)  By  heating  in  a  sealed  tube  with  fuming  nitric  acid  and 
nitrate  of   silver,   when   the   haloid   silver  salt  is   produced 
(Carius). 

Testing  for  Sulphur: 

(a)  In  many  cases,  upon  boiling  with  an  alkaline  solution 
of  lead  oxide,  brown  sulphide  of  lead  is  formed  (e.g.  white  of 

egg); 

(b)  By  heating  with  sodium,  and  testing  the  resulting  sodium 
sulphide  with  water  upon  a  silver  coin  (black  stain);  or  by 
means  of  sodium  nitroprusside  solution  (purple-violet  colora- 
tion) (Schonri); 


4  INTRODUCTION 

(c)  By  complete  oxidation  in  the  dry  way,  by  fusing  with 
potassium  carbonate  and  nitre,  or  by  heating  with  mercuric 
oxide  and  sodium  carbonate;  or  in  the  wet  way,  by  fuming 
nitric  acid  (Carius),  and  testing  the  sulphuric  acid  produced, 
by  barium  chloride  solution. 

In  like  manner  Phosphorus  is  converted  by  complete  oxida- 
tion into  phosphoric  acid;  or,  upon  heating  with  powdered 
magnesia,  and  moistening  the  resulting  mass  with  water, 
the  presence  of  phosphuretted  hydrogen  can  be  recognized 
(Schonn). 

All  the  other  Elements  are  tested  for,  after  complete  oxida- 
tion of  the  compound  (preferably  by  Carius'  method),  in  the 
usual  way. 

Another  method  (B.  1904,  37,  2155)  is  to  heat  a  small 
amount  of  the  substance  with  sodium  peroxide  and  twenty- 
five  times  its  weight  of  naphthalene  or  cinnamic  acid  in  an 
iron  tube,  and  then  test  for  haloids,  sulphates,  phosphates,  &c. 

Quantitative  Organic  or  Elementary  Analysis 

Estimation  of  Carbon  and  Hydrogen  (Combustion).  The 
substance  is  oxidized  by  heating  it  to  redness  with  cupric 
oxide  (Liebig),  or  with  other  substances  which  readily  give  up 
oxygen,  such  as  lead  chromate,  platinum  and  oxygen  (Denn- 
stedt)*  &c.,  in  a  tube  of  difficultly  fusible  glass,  which  is 
open  either  at  one  or  at  both  ends. 

The  carbon  dioxide,  thus  produced  by  the  oxidation  of  the 
carbon,  is  absorbed  by  a  concentrated  solution  of  caustic  pot- 
ash contained  in  specially  shaped  bulbs,*  and  the  water,  pro- 
duced by  the  oxidation  of  the  hydrogen,  in  a  U-shaped  calcic 
chloride  tube,  both  tubes  being  weighed  before  and  after  the 
combustion.  If  the  substance — (0'2  to  0*3  grm.) — is  solid,  it 
is  either  mixed  with  fine,  dry  copper  oxide  (Liebig,  Jlunsen),  or 
placed  in  a  porcelain  or  platinum  boat  and  burnt  in  a  stream 
of  air  or  oxygen  (open  tube).  Liquids  are  weighed  out  in 
small  tubes  or  thin  sealed  glass  bulbs.  When  nitrogen  is 
present,  a  coil  of  tightly -rolled  copper-wire  gauze  is  placed 
in  the  front  part  of  the  combustion  tube  and  heated  to  red- 
ness, in  order  to  reduce  any  oxides  of  nitrogen  which  may 
be  formed  in  the  subsequent  combustion.  In  the  presence  of 
sulphur  or  of  the  halogens,  lead  chromate,  which  has  been 

*  For  details  see  Sudborough  and  James'  Practical  Organic  Chemistry, 
Chap.  V,  B. 


QUANTITATIVE  ANALYSIS  6 

fused  and  then  powdered,  is  used  instead  of  copper  oxide,  so 
as  to  convert  any  Cl,  S02,  &c.,  into  PbCl2,  PbS04,  &c.,  and  thus 
prevent  them  from  passing  into  the  potash  solution.  When 
only  halogens,  without  sulphur,  are  present,  the  combustion  is 
carried  out  with  copper  oxide,  a  copper,  or  still  better  a  silver 
spiral,  which  is  kept  cool,  being  placed  in  the  fore-part  of  the 
tube  to  retain  the  halogens. 

In  the  presence  of  alkalis  or  alkaline  earths  (which  would 
retain  carbon  dioxide),  lead  chromate  mixed  with  -^  of  its 
weight  of  potassic  bichromate  is  used;  the  chromic  acid  then 
expels  all  the  carbonic  acid. 

Explosive  compounds  must  be  burnt  in  a  vacuum.  From 
the  weights  of  carbon  dioxide  and  water  found,  the  percentages 
of  C  and  H  are  readily  calculated: 

C  =  AC02;  H  =   iHs(X 

Estimation  of  Nitrogen.  This  estimation  is  either  relative 
or  absolute.  In  the  former  case  the  proportion  between  the 
nitrogen  and  the  carbon  dioxide  evolved  is  determined  (LieUg, 
Bunsen);  in  the  latter  the  nitrogen  is  either  estimated  as  such 
volumetrically,  or  as  ammonia. 

The  conversion  into  Ammonia  is  effected  by  heating  the 
substance  strongly  with  soda-lime  (Will,  Farrentrapp),  or  by 
creating  it  with  strong  sulphuric  acid  and  permanganate  of 
potash  (Kjeldahlj  Z.  Anal.  Ch.  22,  366;  also  B.  19,  Kef.  852; 
24,  3241;  27,  1633).  The  ammonia  is  then  either  titrated 
directly  by  absorption  in  standard  acid,  or  transformed  into 
ammonium  platinichloride,  (NH4)2PtCl6,  which  is  weighed, 
or  else  ignited,  and  the  weight  of  the  residual  metallic  pla- 
tinum noted. 

In  the  Gasometric  Estimation  of  Nitrogen  the  substance  is 
mixed  with  copper  oxide,  a  copper  spiral  being  also  used  in 
the  front  part  of  the  tube,  and  the  combustion  is  carried  out 
in  the  usual  way,  but  in  a  stream  of  carbon  dioxide;  the  C02 
is  either  generated  from  magnesite  in  the  tube  itself,  or  led 
through  it.  The  nitrogen  is  collected  over  mercury  and 
aqueous  caustic  potash  (Dumas),  or  directly  over  potash 
(ZulkowsJcy,  Schwarz,  Scliiff,  &c.),  in  some  special  form  of 
nitrometer. 

Its  percentage  is  obtained  by  reducing  the  volume  to  the 
volume  at  normal  temperature  and  pressure,  determining  the 
-weight  of  this  volume  of  nitrogen  from  the  fact  that  1  c.c.  of 


6  INTRODUCTION 

dry  nitrogen  at  0°  and  760  mm.  weighs  1*2489  mg.,  and  ex- 
pressing the  result  in  percentage. 

The  Gasometric  method  may  be  used  for  all  classes  of 
nitrogen  compounds,  but  the  Soda-lime  method  cannot  be  used 
for  nitro  compounds,  certain  bases,  and  various  other  groups 
of  compounds,  as  the  nitrogen  of  these  is  not  completely 
transformed  into  ammonia  upon  heating  with  soda-lime. 

For  the  simultaneous  determination  of  carbon,  hydrogen, 
and  nitrogen  the  combustion  must  be  carried  on  in  a  stream 
of  pure  oxygen,  the  mixture  of  gases  escaping  from  the  potash 
bulbs  being  collected  over  a  solution  of  chromous  chloride, 
which  absorbs  the  oxygen,  but  not  the  nitrogen  (A.  1886, 
233,  375). 

Estimation  of  Sulphur  and  Phosphorus.  The  Sulphur  is 
estimated  as  sulphuric  acid,  being  converted  into  this — 

(a)  In  the  wet  way,  by  heating  the  substance  with  fuming 
nitric  acid  at  150°-300°  in  a  sealed  tube  (Carius),  or  in  a  com- 
bustion-tube in  a  mixed  stream  of  nitric  oxide  and  oxygen 
(Claessori),  or  nitric  acid  vapour  (Klasori). 

(b)  In  the  dry  way — (and  this  method  is  only  available  in 
the  case  of  the  less  volatile  compounds) — by  fusing  the  sub- 
stance with  potassic  hydroxide  and  nitre,  or  with  soda  and 
chlorate  or  chromate  of  potash,  also  by  heating  with  soda  and 
mercuric  oxide,  or  with  lime  in  a  stream  of  oxygen. 

Phosphorus  is  estimated  by  analogous  methods. 
Estimation  of  the  Halogens.     Here  also  the  organic  sub- 
stance is  completely  decomposed — 

(a)  After  Carius,  as  above,  in  a  sealed  tube,  with  fuming 
nitric  acid  and  solid  silver  nitrate,  by  which  means  the  halogen 
is  converted  into  its  silver  salt; 

(b)  By  heating  the  compound  strongly  with  pure  lime  in  a 
hard  glass  tube,  or  in  two  crucibles,  one  of  which  is  inverted 
in  the  other,  or  with  sodic  carbonate  and  nitre  in  a  tube.     The 
chloride  formed  is  precipitated  with  silver  nitrate  in  the  usual 
way; 

(c)  By  the  action  of  nascent  hydrogen  (sodium  and  alcohol), 
the  halogen  in  the  organic  substance  can  frequently  be  con- 
verted into  its  hydrogen  compound  (Stepanow). 

Dennstedt,  B.  1897,  30,  1590,  2861,  has  described  methods 
for  estimating  C,  H,  Cl,  and  S  in  one  operation. 

Metallic  and  acidic  radicals,  contained  in  organic  salts,  can 
often  be  estimated  directly  by  the  usual  methods. 

Oxygen  is  almost  invariably  determined  by  difference  j  direct 


DETERMINATION   OF  MOLECULAR  WEIGHT  7 

methods  of  estimation  have  been  proposed  by  Baumhauer,  Laden- 
burg,  Stromeyer,  and  others. 

The  carbon  estimation  is  usually  too  low  (0"05  —  O'l),  owing 
to  leakage  and  incomplete  absorption,  that  of  hydrogen  too 
high  (0-1  —  0'2),  owing  to  the  difficulty  of  completely  drying 
the  cupric  oxide.  Nitrogen  estimations  are  also  usually  too 
high,  owing  to  the  difficulty  of  completely  freeing  the  carbon 
dioxide  from  air. 

The  Calculation  of  the  Empirical  Formula 

The  same  principle  applies  here  as  in  the  case  of  inorganic 
compounds,  i.e.  the  percentage  numbers  found  are  divided  by 
the  atomic  weights  of  the  respective  elements,  the  relative  pro- 
portions of  the  quotients  obtained  being  expressed  in  whole 
numbers.  For  instance,  acetic  acid  being  found  to  contain 
40-11  p.c.  carbon,  6 '80  p.c.  hydrogen,  and,  consequently,  53*09 
p.c.  oxygen,  the  quotients  are  to  each  other  as  3-34  :  6 -80  :  3 -32 
=  1:2:1.  The  simplest  analysis-formula  of  acetic  acid  would 
therefore  be  CH20.  Sometimes  figures  are  obtained  which 
correspond  with  equal  nearness  to  different  formulae,  between 
which  it  is  therefore  impossible,  without  further  data,  to 
choose. 

For  instance,  a  sample  of  naphthalene  yields  on  analysis 
93-70  p.c.  carbon  and  6 '30  p.c.  hydrogen;  the  quotient  pro- 
portion here  is  7 -81  to  6'30  =  1-239:1,  which  corresponds 
equally  well  with  the  numbers  5:4  or  11:9.  The  formula 
C5H4  requires  93'75  p.c.  carbon  and  6-25  p.c.  hydrogen,  and 
the  formula  CnH9,  93-62  p.c.  carbon  and  6*38  p.c.  hydrogen, 
the  deviations  from  the  actual  numbers  found  being  in  both 
cases  within  the  limits  of  experimental  error.  Therefore  other 
considerations  must  be  taken  into  account  here,  in  order  to 
decide  between  the  two  formulae. 

The  formula  derived  from  the  results  of  analyses  is  termed 
the  Empirical  Formula,  and  expresses  the  simplest  numerical 
relationship  between  the  atoms  of  the  elements  present.  The 
actual  molecular  formula  may  be  a  multiple  of  this,  and  has  to 
be  determined  according  to  special  principles. 

Determination  of  Molecular  Weight 

1.  BY  CHEMICAL  METHODS. 

Our  chemical  formulae  (e.g.  CH20)  express  not  merely  a 


8  INTRODUCTION 

percentage  relation,  but  at  the  same  time  the  smallest  quantity 
of  the  compound  which  is  capable  of  existing  as  such,  i.e.  a 
molecule  of  it.     This  molecule  is  ideally  no  longer  divisible  '  * 
mechanical  means,  but  only  by  chemical,  and  then  into  its  J 
stituent  atoms.     If  the  formula  CH20  were  the  correct  on/f( 
acetic  acid,  then  the  amount  of  oxygen  (or  carbon)  contained  ii 
a  molecule  would  be  indivisible,  and  that  of  hydrogen  divrsibl 
only  by  2.     Since,  however,  it  has  been  observed  that;  on< 
fourth  of  the  total  hydrogen  in  acetic  acid  is  replaceable,  e.l 
by  a  metal,  with  the  formation  of  a  salt,  it  is  obvious  that  ' ' 
quantity  of  hydrogen  in  the  molecule  must  be  divisible 
and  so  the  formula  must  contain  at  least  4  atoms  of  hydro^ 
and  must  therefore  be  C2H402,  or  some  multiple  of  it.     1 
is,  in  fact,  the  case.    Acetate  of  silver  contains  64 '67  p.c.  sil1 
and  therefore  35*33  p.c.  of  the  acetate  radical;  or,  to  1  aton 
silver  =108  parts  by  weight,  there  are  59  parts  by  weigh] 
the  acid  radical.     This  59,  together  with  1  atom  of  hydro! 
=  1,  makes  the  molecular  weight  of  acetic  acid  60,  =  2  x 
=  2  x  CH20,   =  C2H402. 

This  is  a  determination  of  molecular  weight  by  chemi 
means.     Such  determinations  are  carried  out  in  the  easel 
acids  generally  by  means  of  their  silver  salts;  these  are  iisi 
normal    salts,    are   easy    to   purify,    are   almost   always 
from  water  of  crystallization,  and  are  readily  analysed, 
is,    however,  absolutely  necessary  to  know   whether   the 
is  mono-  or  polybasic.     In  the  case  of  a  di-,  tri-,  &c.,  basic 
the  above  calculation  must  be  made  with  reference  to  2, 
&c.,  atoms  of  silver,  whereas  acetic  acid — being  monobasic! 
contains  only  one   replaceable  atom  of   hydrogen,  which  \ 
therefore  exchanged  for  one  atom  of  silver.     Consequent^, 
its  formula  cannot  be  a  multiple  of  C2H402. 

In  the  determination  of  the  molecular  weights  of  Bases,  theii 
platinichlorides  are  similarly  made  use  of,  these  being  almost 
always  constituted  on  the  type  of  ammonium  platinichloride : 
(NH3)2H2PtCl6 :  i.e.  they  contain  two  molecules  of  a  mono- 
acid  base  such  as  ammonia  combined  with  one  atom  of 
platinum. 

To  determine  the  molecular  weights  of  Neutral  Compounds, 
derivatives  must  be  prepared  and  examined  for  the  proportion 
of  the  total  hydrogen  which  is  replaceable,  e.g.,  by  chlorine. 
For  example,  by  the  action  of  chlorine  upon  naphthalene, 
there  is  first  formed  the  substance  monochloronaphthalene, 
which  contains  73'8  per  cent  0,  4 -3  per  cent  H,  and  21-9  per 


DETERMINATION   OF  MOLECULAR  WEIGHT  9 

cent  Cl,  these  numbers  giving  the  formula  C10HrCl.  In  the 
same  way  benzene  yields  the  compound  C6HcCl.  In  both 
these  cases  the  halogen  ajts  by  replacing  hyarogen,  and  at 
least  one  atom  of  the  latte  •  in  the  molecule  must  be  replaced, 
since  fractions  of  an  atom  are  necessarily  out  of  the  question. 
If,  then,  the  compound  oltained  has  the  formula  C10H7C1,  it 
follows  that  |^th  of  the  H  present  has  been  replaced  by  Cl, 
and  there  must  consequently  be  8,  8  X  2,  or  8  X  3,  &c.,  atoms 
of  hydrogen  in  the  compound,  and  likewise  10  atoms,  or  some 
multiple  of  10,  of  carbon.  But  a  multiple  of  8  or  10  may  be 
rejected,  since  no  compounds  have  been  observed  which  would 
indicate  the  replacement  of  TVth  of  the  total  hydrogen.  This 
leads  to  the  formula  C10H3  for  naphthalene,  the  other  possible 
formula  got  by  analysis  viz.  CnH9  (see  p.  7),  being  now 
untenable.  In  a  similar  way  the  formula  of  benzene  is  found 
to  be  C6H6. 

2.  BY  PHYSICAL  METHODS. 

(a)  By  Estimating  the  Fapour  Density. 

According  to  the  law  of  Avogadro  (1811)  and  Ampere  (1814), 
all  gases  under  similar  conditions,  i.e.  in  the  perfectly  gaseous 
state  and  under  the  same  temperature  and  pressure,  contain  in 
equal  volumes  equal  numbers  of  molecules.  It  follows  from 
this  that  the  weights  of  equal  volumes  of  different  gases  are 
proportional  to  the  weights  of  equal  numbers  of  their  con- 
stituent molecules,  in  other  words,  the  molecular  weight  is 
proportional  to  the  specific  gravity  of  the  gas.  Thus,  if  Mx  be 
the  molecular  weight  of  any  given  substance  required,  M0 
that  of  oxygen,  S  the  vapour  density  or  specific  gravity  of  the 
former  as  compared  with  oxygen  taken  as  16*, 

MX:M0   =   S:16. 

And  since  M0  =  32,  Mx  =  S  X  2.  To  determine,  therefore, 
the  molecular  weight  of  a  gas  or  vapour,  one  has  only  to  find 
its  density,  and  to  multiply  this  by  2. 

To  take  an  example,  the  specific  gravity  of  acetic  acid 
vapour  being  found  to  be  30,  then  M  =  60,  and  the  mole- 
cular formula  is  C2H402  =  60. 

*  Oxygen  is  taken  as  standard  (0  =  16)  for  vapour  density,  since  it  is  now 
customary  to  take  it  as  standard  in  atomie-weight  determinations.  For  all 
practical  purposes,  one  may  take  the  density  compared  with  hydrogen  as 
unity. 


16  INTRODUCTION 

It  is  essential  to  the  application  of  this  method  that  the 
temperature  of  the  vapour  shall  be  so  high  above  the  boiling- 
point  of  the  substance  that  the  latter  is  in  the  perfectly  gaseous 
state,  remaining  at  the  same  time  undecomposed. 

The  only  common  method  employed  in  the  chemical  labora- 
tory for  vapour-density  determinations  is  that  due  to  Victor 
and  Carl  Meyer.  In  this  process  the  small  tube  containing 
the  substance  is  dropped  into  a  vertical  glass  tube,  the  lower 
and  wider  part  of  which  is  cylindrically  shaped  and  sealed. 
This  is  kept  warm  at  a  constant  temperature,  being  surrounded 
by  a  long  glass  mantle  in  which  a  suitable  liquid  boils,  the 
upper  part  of  the  mantle  itself  serving  for  the  condensation  of 
the  vapour.  The  displaced  air  alone  escapes,  and  is  collected 
over  water  and  measured.  No  determination,  therefore,  of 
the  temperature  of  the  vapour  of  the  substance  in  question  is 
required.  Only  about  Ol  grm.  substance  is  required.  In  all 
cases  the  vapour  density  is  the  weight  of  the  vapour,  divided 
by  the  weight  of  an  equal  volume  of  hydrogen  (see  note,  p.  9), 
which  can  readily  be  calculated  in  the  usual  manner. 

If,  instead  of  having  the  apparatus  filled  with  air,  hydrogen 
is  employed,  the  greater  molecular  velocity  of  the  latter 
allows  of  the  conversion  of  substances  into  vapour  at  30°-40° 
below  their  ordinary  boiling  temperatures  (V.  Meyer  and  De- 
muth,  B.  1890,  23,  311). 

Until  a  few  years  ago,  the  determination  of  molecular  weights 
by  physical  means  was  restricted  to  the  different  modifications 
of  the  method  which  has  just  been  described,  and  consequently 
it  could  only  be  carried  out  with  substances  which  were  either 
already  gaseous,  or  which  could  be  rendered  so  without  decom- 
position. 

The  recent  important  researches  of  van't  Hoff,  Eaoult,  Ar- 
rhenius,  Ostwald,  and  others,  upon  the  nature  of  solution — in 
particular,  the  proof  that  the  laws  of  Boyle,  Gay-Lussac,  and 
Avogadro  are  applicable  to  solutions  as  well  as  to  gases — now 
permit,  however,  of  the  ready  determination  of  the  molecular 
weights  of  substances  in  solution,  and  therefore  of  compounds 
which  could  not  be  volatilized  without  decomposition.  This  is  accom- 
plished as  follows : — 

(b)  By  Measuring  the  Depression  of  the  Freezing  Tempera- 
ture of  Solutions,  or  Cryoscopic  Method. 

This  method  is  based  upon  the  following  data : — Each  solvont 
has  a  perfectly  definite  freezing-point  (e.g.  water  0°,  benzene, 


DETERMINATION   OF  MOLECULAR  WEIGHT  11 

5'0°,  and  glacial  acetic  acid,  16-75°),  but  the  introduction  of  a 
solute  into  such  a  solvent  lowers  the  freezing-point,  and  within 
certain  limits  the  lowering  is  directly  proportional  to  the  con- 
centration of  the  solute.  Raoult  has  shown  that  gram  mole- 
cules of  different  substances  dissolved  in  equal  weights  of  the 
same  solvent  lower  the  freezing-point  of  the  solvent  to.  the 
same  extent,  or  "  equimolecular  solutions  have  the  same 
freezing-point ".  The  molecular  lowering  of  the  freezing-point 
is  the  lowering  which  would  be  produced  when  ,the  gram 
molecule  (M)  of  the  substance  was  dissolved  in  100  grams  of 
solvent,  and  is  usually  denoted  by  C.  This  varies  for  different 
solvents,  and  may  be  determined  experimentally  by  using 
substances  of  known  molecular  weight,  e.g.,  p  grams  of  a  sub- 
stance of  molecular  weight  M  dissolved  in  100  grams  of 
solvent  caused  a  depression  of  A°  in  the  freezing-point  of 
the  solvent. 

'A  =  depression  for  p  grams  in  100  grams  of  solvent 


M        „        100 
.  C  =  M|- 


The  value  C  may  also  be  calculated  theoretically  from  van't 

2T2 

Hoffs  equation  C   =  ,  where  T  =.  absolute  freezing- 

100  L 

point  of  the  solvent,  and  L  is  the  latent  heat  of  fusion  of  the 
solvent. 

Having  determined  the  value  C  (for  water  C  =  18-5,  for 
glacial  acetic  acid  39,  and  for  benzene  50),  we  may  use  the 
same  equation 

C  =  M-    or    M  =  9? 
p  A 

for  calculating  M  when  A  =  lowering  of  the  freezing-point 
produced  by  dissolving  p  grams  of  a  substance  of  unknown 
molecular  weight  M  in  100  grams  of  solvent. 

It  is  obvious  that  this  method  cannot  be  employed  with 
satisfactory  results  for  determining  the  molecular  weights  of 
electrolytes  in  ionizing  media.  It  has  also  been  found  that 
certain  hydroxylic  substances  give  abnormal  values  in  benzene 
solution,  owing  to  the  fact  that  benzene  tends  to  cause  the 
association  of  molecules  of  such  compounds. 

Ebulliscopic  Method.  Molecular  weights  may  also  be 
determined  by  the  raising  of  the  boiling-point  of  a  suitable 


12  INTRODUCTION 

solvent  produced  by  the  introduction  of  known  weights  of 
the  substance  into  a  given  weight  (or  volume)  of  the  solvent. 
The  principles  involved  are  exactly  the  same  as  those  dis- 
cussed above  in  the  cryoscopic  method,  but  the  forms  of 
apparatus  are  different.  (J.  C.  S.  1898,  73,  502.) 

Descriptions  of  apparatus  employed  in  these  physical 
methods  are  given  in  Sudborough  and  James'  Practical  Or- 
ganic Chemistry,  Chap.  VIII. 

(c)  By  Measurement  of  the  Osmotic  Pressure. 
According  to  van't  Hoff  (Z.  phys.  Chem.  I.  481),  equimole- 

cular  solutions  exert  the  same  osmotic  pressure,  or  are  isotonic, 
equality  of  temperature  being  assumed.  From  this  it  follows, 
by  reasoning  analogous  to  that  in  section  (&),  that  the  mole 
cular  weight  of  a  compound  can  be  ascertained  by  measuring 
the  osmotic  pressure  of  its  solution.  The  method  is  rarely 
used  in  chemical  laboratories.  (Ladenburg,  B.  1889,  22,  1225; 
M.  Planck,  Z.  phys.  Chem.,  1890,  6,  187.) 

(d)  By  Measurement  of  the  Lowering  of  the  Vapour  Pressure. 

According  to  Eaoult,  the  same  generalizations  hold  for  the 
lowering  of  the  vapour  pressure  of  a  solvent  by  the  introduc- 
tion of  a  solute,  as  for  the  lowering  of  the  freezing-points  or 
the  raising  of  the  boiling-point.  Three  methods  of  applying 
the  principle  for  the  determination  of  molecular  weights  have 
been  described.  This  law  can  be  deduced  theoretically  from  the 
preceding  one  (c),  and  it  also  stands  in  theoretical  continuity 
with  that  of  (b).  (See  Will  &  Bredig,  B.  1889,  22,  1084; 
Barger,  J.  C.  S.  1904,  85,  206;  Perman,  ibid.  1905,  87,  194; 
Blacbnan,  ibid.  1474.) 

(e)  By  Measuring  the  Decrease  in  Solubility. 
(Nernst,  B.  23,  Eef.  619.     See  also  Ostwald-Luther.) 

Polymerism  and  Isomerism 

The  determination  of  molecular  weight  is  of  the  first  im- 
portance, because  different  substances  very  frequently  have  the 
same  percentage  composition  and  therefore  the  same  empirical 
formula,  and  yet  are  totally  distinct  from  one  another.  This 
difference  is  often  due  to  differences  in  the  complexities  of  the 
molecules.  Thus  formic  aldehyde,  CH00;  acetic  acid,  C2H402; 
lactic  acid,  C3H603;  and  grape-sugar,  C6H120G,  have  all  the 
same  percentage  composition;  as  have  also  ethylene,  C2H4; 


THEORY  OF  VALENCY  13 

propylene,  C3H6;  and  butylene,  C4H8.  Compounds  standing 
in  such  relation  to  each  other  are  termed  polymers.  Very 
frequently,  however,  substances  which  are  totally  distinct 
from  each  other  possess  both  the  same  percentage  composition 
and  the  same  molecular  weight;  that  is  to  say,  these  com- 
pounds are  made  up  not  only  of  the  same  elements,  but  also 
of  an  equal  number  of  atoms  of  these  elements;  such  sub- 
stances are  termed  isomers  or  metamers.  (See  Ethers.) 
Thus,  for  instance,  common  alcohol  and  methyl  ether,  the 
latter  of  which  is  obtained  by  heating  methyl  alcohol  with  sul- 
phuric acid,  have  one  and  the  same  molecular  formula,  C2H60. 
The  striking  phenomenon  of  isomerism  is  most  readily  ex- 
plicable on  the  assumption  that  for  the  molecule  of  each  com- 
pound there  is  a  definite  arrangement  of  the  atoms,  and  that 
this  arrangement  or  grouping  is  different  in  the  molecules  of 
the  two  isomerides.  This  difference  in  grouping  may  be  con- 
sidered as  being  due  to  a  difference  in  the  linking  powers  of 
the  atoms,  as  is  indicated  by  the  dissimilar  chemical  behaviour 
of  isomers,  and  explained  by  the  theory  of  valency. 

Chemical  Theories;  the  Theory  of  Valency 

After  the  fall  of  the  Electro  -  Chemical  theory,  unitary 
formulae — in  contradistinction  to  the  earlier  dualistic  formulae 
— were  much  used;  thus  alcohol  had  the  formula  C4H602 
(using  the  old  equivalent  weights).  The  necessity  for  com- 
paring substances  of  complicated  composition  with  simpler 
ones,  taken  as  "  Types ",  had  already  repeatedly  led  to  the 
propounding  of  new  theories  for  representing  the  constitution 
of  organic  compounds,  e.g.  the  older  Type  theory  (Dumas),  and 
the  Nucleus  theory  (Laurent). 

These  obtained  a  firmer  basis  through  Gerhardfs  Theory  of 
Types,  which  received  support  more  especially  from  the  dis- 
covery of  ethylamine  and  other  ammonia  bases  (Wurtz,  1849, 
and  Hofmann,  1849,  1850),  the  proper  interpretation  of  the 
formulae  of  the  ethers  (Williamson,  1850),  and  the  discovery 
of  the  acid  anhydrides  (GerharcU,  1851).  All  compounds, 
inorganic  as  well  as  organic,  were  in  this  way  compared  with 
simpler  inorganic  substances  taken  as  "  Types",  of  which 
Gerhardt  named  four,  viz. — 


\  H\  H10  SUr 

I  ClI  H/°  ||N 


14  INTRODUCTION" 

The  first  two  of  these  really  belong  to  the  same  type.     Thus 
the  following  formulae  were  arrived  at:  — 

•  :      g}       5) 

Potassium  chloride  Ethyl  chloride          Acetyl  chloride 


)0  1)0  NH°»}0 


Potassium  hydroxide     Nitric  acid  Alcohol  Acetic  acid 


Potassium  oxide   Nitric  anhydride  Ether  Acetic  anhydride 

C2H6)  C2H30) 

H    ^N  H     VN 

H  J  H    J 

Ethylamine  Acetamide 

&c.  &c.  Organic  compounds  could  thus,  like  inorganic,  be 
referred  to  inorganic  types  by  assuming  in  them  the  presence 
of  Radicals  (e.g.  ethyl,  C2H5;  acetyl,  C2H30,  &c.),  i.e.  of  groups 
of  atoms  which  play  a  part  analogous  to  that  of  an  atom  of 
an  element,  and  which  can  be  transferred  by  double  decom- 
position from  one  compound  to  another.  Thus  ethyl  chloride, 
C2H5C1;  alcohol,  C2H§0;  ethylamine,  C2H7N;  ether,  C4H100; 
&c.,  were  represented  as  containing  the  same  radical  C2H5, 
ethyl,  and  the  close  relationship  existing  between  these  com- 
pounds now  found  expression  in  the  type  formulae. 

Sulphuric  acid,  H2S04,  was  derived  from  the  double  water- 
type,  thus — 


and  chloroform,  CHC13,  and  glycerin,  C3H803,  from  the  triple 
hydrochloric  acid  and  water  types — 


the  assumption  being  made  that  the  radicals  (C2H5)',  (S02)", 
(CH)"',  and  (C3H5)"'  could  replace  a  number  of  hydrogen  atoms 
corresponding  with  the  number  of  accents  (')  marked  upon  them, 
%,e.  that  they  were  monatomic,  diatomic,  &c.  To  the  above 


THEORY  OF  VALENCY  16 

three  types  KekuU  afterwards  added  a  fourth,  of  especial  im- 
portance as  regards  the  carbon  compounds,  viz. — 


It  was  then  found  that  many  compounds  could  be  referred 
equally  well  to  one  or  another  of  these  types,  methylamine, 
for  instance,  either  to  CH4  or  to  NHg,  thus — 

CH,} 
or      H  IN. 


The  assumption,  already  mentioned,  of  the  atomic  groups 
(radicals)  which  in  these  types  replaced  hydrogen,  led  further 
to  more  exact  investigations  of  the  chemical  value,  i.e.  the 
replaceable  value,  of  those  groups  as  compared  with  that  of 
hydrogen.  In  this  way  chemists  Learnt  to  distinguish  between 
mono-,  di-,  tri-,  &c.,  valent  groups,  and,  generally  speaking,  to 
pay  more  attention  to  equivalent  proportions. 

As  the  outcome  of  his  researches  upon  organo-metallic  com- 
pounds, Frankland  formulated  in  1852  (A.  85,  368)  the  law 
that  the  elements  nitrogen,  phosphorus,  arsenic,  and  antimony 
tend  to  form  compounds  which  contain  three  or  five  equivalents 
of  other  elements. 

KekuU  then,  in  1857-58  (A.  104,  129;  106,  129),  proceeded 
to  show  that  a  more  profound  idea  (the  "  Type  idea  ")  lay  at 
the  root  of  the  types  themselves,  viz.,  that  there  are  mono-, 
di-,  tri-,  and  tetra valent,  &c.,  elements,  which  possess  a  corre- 
sponding replacing  or  combining  value  as  regards  hydrogen; 
and  that  hydrogen  is  therefore  monovalent,  oxygen  divalent, 
nitrogen  trivalent,  carbon  tetravalent,  and  so  on. 

With  the  introduction  of  the  CH4  type  by  Kekuli,  and  the 
establishment  of  the  tetravalent  nature  of  the  carbon  atom 
accompanying  this,  were  connected  the  endeavours  of  Kolbe 
to  derive  the  constitution  of  organic  compounds  from  carbonic 
acid  (according  to  Kolbe  C204,  C  =  6,  0  =  8),  by  the  ex- 
change of  oxygen  for  organic  radicals  (A.  113,  293);  see  also, 
for  further  details,  Kopp's  "  Entwickelung  der  Chemie  in  der 
neueren  Zeit"  (Oldenbourg,  Munich,  1873),  and  E.  V.  Meyer's 


16  INTRODUCTION 

"  History  of  Chemistry  "  (Macmillan,  1891),  Schorlemmer's  "Rise 
and  Development  of  Organic  Chemistry  "  (Macmillan). 

The  question  of  the  valency  of  elements,  a  point  which  it  Is 
often  difficult  to  decide  in  inorganic  chemistry,  is  infinitely 
easier  of  determination  in  the  case  of  the  carbon  compounds, 
because  the  carbon  atom  is  tetravalent  towards  hydrogen  as 
well  as  towards  chlorine  and  oxygen.  Since  the  atom  of 
hydrogen,  as  the  unit  of  valency,  is  monovalent,  and,  further, 
since  the  divalence  of  the  oxygen  atom  cannot  reasonably  be 
doubted,  the  valency  of  the  three  "  organic  "  elements  hydrogen, 
oxygen,  and  carbon  may  be  considered  as  resting  upon  a  sure 
basis,  as  may  also  the  conclusions  drawn  therefrom,  and  this 
all  the  more  since  the  most  important  carbon  compounds  are 
made  up  of  those  three  elements. 

Within  the  past  few  years  the  divalency  of  the  oxygen 
atom  in  many  organic  compounds  has  been  brought  into  ques- 
tion. The  readiness  with  which  many  oxy-derivatives  form 
definite  compounds  with  mineral  acids  and  with  metallic  salts 
would  appear  to  indicate  that  in  many  cases  the  oxygen  atom 
can  even  be  tetravalent  (see  Oxonium  Salts).  In  certain  com- 
pounds it  has  also  been  suggested  that  the  carbon  atom  may 
be  trivalent  (see  Triphenylmethyl). 

Explanation  of  Isomerism;  Determination  of  the 
Constitution  of  Organic  Compounds 

The  phenomenon  known  as  isomerism  is  elucidated  to  a 
great  extent  by  the  theory  of  valency.  If  two  substances 
have  the  same  molecular  formula,  i.e.  both  contain  the  same 
elements  and  the  same  number  of  atoms  of  the  respective 
elements  in  their  molecules,  then  the  obvious  conclusion  to 
be  drawn  is  that  in  the  two  molecules  the  atoms  are  differently 
arranged.  The  methods  adopted  in  determining  the  manner 
in  which  the  atoms  are  linked  together,  or,  as  it  is  called,  the 
determination  of  the  chemical  constitution  of  the  compound, 
is  usually  based  on  the  following  points: — (a)  The  respective 
valencies  of  the  atoms  constituting  the  molecule.  A  compound 

C9EL  must  have  the  structural  formula  H-)C»C^-H,  or,  as 

H/       XH 

it  is  often  more  shortly  written,  CH3»CH3,  if  each  atom  of 
carbon  is  to  be  represented  as  tetravalent,  and  each  hydrogen 
atom  as  monovalent.  Similarly  the  compound  CH40  must  be 


DETERMINATION   OF  CONSTITUTION  17 

TT  TT 

represented  as  TTX^XO  _  H'  or  ^3  '  ^"^  ^  ^e  car^on  atom 
j^  tetravalent,  the  oxygen  atom  divalent,  and  the  hydrogen 
atoms  monovalent.  (b)  A  study  of  the  more  important  methods 
of  formation  and  of  the  chemical  reactions  in  which  the  com- 
pound in  question  can  take  part.  To  select  as  an  example 
ethyl  alcohol,  C2H60.  We  can  start  from  ethane,  CH3»CH3, 
and  by  the  action  of  chlorine  replace  one  of  the  hydrogen 
atoms  by  a  chlorine  atom,  and  thus  obtain  the  compound 
CH3.CH2C1.  When  this  is  boiled  with  dilute  alkalis  (KOH), 
it  gives  potassic  chloride  and  ethyl  alcohol,  C2H5C1  +  KOH  = 
C2H60  -f  KC1.  From  this  it  is  obvious  that  the  monovalent 
chlorine  atom  becomes  replaced  by  an  atom  of  oxygen  and 
an  atom  of  hydrogen.  This  can  be  readily  understood  if 
we  assume  that  these  two  atoms  enter  in  the  form  of  the 
monovalent  hydroxyl  group,  —  O  —  H,  and  the  constitutional 

Hv  /H 

formula  for  ethyl  alcohol  would  then  be  H-^C  —  C^-H 

W  X)—  H 

CH3«CH2«OH.  This  formula  is  further  supported  by  a  study 
of  most  of  the  chemical  reactions  in  which  ethyl  alcohol  can 
take  part.  It  can  react  with  metallic  sodium,  yielding  a  com- 
pound, sodic  ethoxide,  C2H5NaO;  however  much  sodium  is 
employed,  only  one  of  the  six  hydrogen  atoms  present  in  the 
alcohol  molecule  can  be  replaced  by  sodium,  and  this  atom  is 
presumably  the  one  differently  situated  from  the  remaining 
five,  namely,  the  one  attached  to  oxygen.  The  presence  of 
the  hydroxyl,  —  0  —  H,  group  is  further  confirmed  by  the 
action  of  hydric  chloride  or  of  phosphorus  trichloride  on  the 
alcohol,  when  an  atom  of  chlorine  takes  the  place  of  the  •  OH 
group. 


or 


and   3CH3.CH2.OH  +  PC13  =  3CH3.CH2C1  +  P(OH)3. 

Isomeric  with  ethyl  alcohol  is  the  substance  known  as 
dimethyl  ether.  Although  it  has  the  same  molecular  formula, 
it  differs  altogether  from  ethyl  alcohol  in  its  chemical  and 
physical  properties.  The  only  other  possible  method  of  link- 

ing up  the  atoms  2C,  6H,  and  0,  is  H^C—  O—  C^H,  in 

which  the  two  carbon  atoms  are  not  directly  united  to  one 
another,  and  in  which  the  six  hydrogen  atoms  are  all  similarly 

(B480)  B 


18  INTRODUCTION 

situated.  The  chemical  reactions  of  dimethyl  ether  are  in  per- 
fect harmony  with  this  constitutional  formula.  It  does  not 
react  with  metallic  sodium,  and  hence  presumably  does  not 
contain  an  »OH  group.  When  acted  upon  by  hydriodic  acid, 
under  suitable  conditions,  the  molecule  is  ruptured,  as  repre 
sented  by  the  following  equation: — 

CHa.O.CH3-f  HI  =  CH3I  +  CH3.OH. 

Similarly,  whenever  the  oxygen  atom  is  removed  a  rupture 
of  the  molecule  occurs,  and  the  two  carbon  atoms  in  the  mole- 
cule become  separated. 

The    constitutional    formula    for    acetic    acid    is    written 

H\  O 

H-pC — C^Q TT-     This  formula  corresponds  perfectly  with 

the  chemical  behaviour  of  acetic  acid  and  explains  the  fol- 
lowing facts: — (a)  that  one  of  the  hydrogen  atoms  of  the  acid 
possesses  properties  different  from  those  of  the  three  others, 
the  first-named  being  easily  replaceable  by  metallic  radicals; 
(b)  that  the  two  oxygen  atoms  behave  differently,  not  being 
equally  readily  exchangeable  for  other  radicals;  (c)  that  dif- 
ferent functions  appertain  to  the  two  carbon  atoms,  so  that 
one  of  them — being  already  joined  to  two  atoms  of  oxygen — 
easily  gives  rise  to  carbonic  acid,  while  the  other — connected 
as  it  is  with  three  atoms  of  hydrogen — readily  passes  into 
methane  or  methyl  compounds. 

On  account  of  the  innumerable  cases  of  isomerism  which 
have  been  observed,  simple  molecular  formulae  alone  are  in 
most  cases  insufficient  for  the  discrimination  of  organic  com- 
pounds; it  generally  requires  the  constitutional  formulae  to 
give  a  clear  idea  of  their  behaviour  and  of  their  relations  to 
other  substances.  Careful  study  has  made  it  possible  within 
the  last  few  decades  to  find  out  the  mode  in  which  the  atoms 
are  combined  in  the  molecules  of  most  organic  compounds,  and 
from  this  to  deduce  new  methods  for  their  preparation.  The 
constitutional  formulas  thus  arrived  at  are  sometimes  very 
simple,  sometimes,  however,  very  complicated,  as,  for  instance, 
in  the  cases  of  citric  acid  and  grape-sugar  (which  see). 


NATURE  OF  CARBON  ATOM  19 

Rational  Formulae 

Great  latitude  is  permissible  as  regards  the  mode  of  writin* 
constitutional  formulae,  according  to  the  particular  points 
which  it  is  desired  to  emphasize.  A  formula  on  paper  is  not 
as  a  rule  intended  to  represent  the  symmetrical  or  spatial 
arrangement  of  the  atoms  in  a  compound. 

A  shortened  constitutional  formula,  which  indicates  more 
chemical  relations  than  an  empirical  one  does,  is  called  a 
rational  formula;  e.g.  C2H5OH,  alcohol;  (CH3)  O,  methyl  ether. 

For  acetic  acid,  instead  of  the  constitutional  formula  already 
given  on  page  18,  the  following  rational  formulas  may  be 
used:  — 

CH3-C<OH,    CH3-CO.OH,    CH3-C02H,    CH3.C02H, 
(CH3.CO)OH,    CSH3O.OH,    H^A);  and  so  on. 


The  Nature  of  the  Carbon  Atom 

The  theoretical  views  and  the  knowledge  thereby  gained  of 
the  nature  of  the  carbon  atom  may  be  expressed  somewhat  as 
follows  :  — 

1.  The  carbon  atom  is  tetravalent. 

2.  Its  four  valencies  are  all  equal;  a  mono-substituted  deri- 
ative  of  methane  exists  in  only  one  form,  that  is,  isomerism  is 
ot  met  with. 

3.  The  atoms  or  atomic  groups  which  are  held  bound  by 
hese  four  valencies  cannot  readily  exchange  places  with  each 
ther  (the  Le  Bel-van  't  Ho/  law,  1874).     Proof:  there  are  in 
early  every  case  two  physically  different  tetra-substitution 
roducts,  C,  a,  b,  c,  d  of  methane  (see  Stereochemistry). 

4.  Several  carbon  atoms  can  be  connected  together  by  either 
ne,  two,  or  three  valencies  (see  p.  23):  C«C,  C:C,  C:C. 

5.  Similarly,  three  or  more  carbon  atoms  may  be  united, 
rming  in  this  way  the  so-called  "carbon  chains"  (see  p.  32), 


nus — 


The  number  of  the  atoms  so  linked  together  may  be  very 
irge,  in  some  cases  probably  several  hundreds. 
6.  These   carbon   atoms   form   either  open   or  ring-shaped 


losed  chains. 


20  INTRODUCTION 

Open  chains  are  those  which  have  separate  constituent  atoms 
at  either  end,  as  in  (5).  In  closed  chains  or  rings,  on  the  con- 
trary, the  first  and  last  constituent  atoms  are  linked  together 
(although  there  may  at  the  same  time  be  subsidiary  branches 
from  them),  thus  — 


A    /x    /V 

A   i,  ^  A   A. 

\- 


c-c-c. 

7.  The  atoms  of  other  elements,  with  the  exception,  of 
course,  of  monovalent  ones,  may  likewise  take  part  in  the 
formation  of  such  chains,  both  open  and  closed;  for  example: 

C  —  Cv  C  —  Cv  sC  —  (X 

c—  <y         c—  c/          \c-cx 

The  above  figures  (the  hexagon,  &c.),  which  are  made  use 
of  to  represent  such  chains  or  rings,  are  merely  meant  to  be 
pictorial  (schematised)  and  not  geometrical;  the  question  of  the 
spatial  arrangement  of  atoms  in  compounds  will  be  dealt  with 
later. 

Homology 

In  the  study  of  carbon  compounds  it  is  customary  to  grou 
together  all  the  compounds  with  similar  chemical  structur 
and  similar  chemical  properties,  and  to  arrange  the  member 
of  such  a  group,  or  homologous  series  as  it  is  termed,  accordin 
to  the  order  of  their  molecular  complexity,  i.e.  according  t 
the  number  of  carbon  atoms  contained  in  the  molecule. 

For  example:  — 

Paraffins.  Fatty  acids. 

methane  ......  CH2O2  formic 

ethane  ......  C2H4O2  acetic 

propane  ......  C3H6O2  propionic 

o  butane  ......  C4H802  butyric 

&c. 

It  is  found  that  in  any  such  homologous  series  a  number  c 
generalizations  can  be  drawn.  Some  of  the  more  important  c 
these  are  :  — 

1.  For  each  homologous  series  we  can  write  a  general  f& 


HOMOLOGOUS  SERIES  21 

mula  which  will  represent  the  composition  of  all  the  members 
of  the  series;  for  example,  the  general  formula  for  the  paraffins 
is  CnH3n+2,  and  for  the  saturated  fatty  acids  Cyi.^^ 

2.  If  any  particular  member  in  a  series  is  selected,  it  is 
found  to  differ  in  composition  from  the  member  immediately 
preceding,  and  also  from  the  one  immediately  succeeding,  it  by 
a  definite  amount,  namely,  CH2.    Or,  expressed  in  other  words, 
any  member  of  the  series  may  be  regarded  as  derived  from 
the  member  immediately  preceding  it  by  the  introduction  of 
a  methyl  group,  »CH3,  for  an  atom  of  hydrogen.     It  follows, 
therefore,  that  all  the  members  of  the  paraffin  series  may  be 
regarded  as  derived  from  GEL  by  the  addition  of  a  given 
number  of  CH2  groups,  and  the  general  formula  is  for  this 
series  CH4  -f-  «CH2,  or  more  simply  0^3^+ a- 

3.  The  chemical  properties  of  the  different  members  of  the 
series  vary  but  slightly,  so  that  a  description  of  the  chemical 
properties  of  any  one  member  may  be  taken,  as  a  rule,  to 
apply  to  the  other  members. 

4.  In  studying  the  physical  properties,  well-marked  grada- 
tions are  observed  as  the  number  of  carbon  atoms  increases. 
In  the  case  of  liquids,  the  boiling-point  is  found  to  rise  as  the 
complexity  of  the  molecule  increases.     In  certain  series,  e.g. 
the  paraffins,  the  first  few  members  are  gases,  then  follow 
liquids  with  gradually  increasing  boiling-points,  and  ultimately 
solids  with  extremely  high  boiling-points.      Other  physical 
data,  such  as  melting-point,  specific  gravity,  solubility,  &c., 
are  affected  in  very  much  the  same  manner. 

In  the  paraffin  series  the  grouping  together  of  the  carbon 
atoms  must  be  conditioned  by  themselves,  since  hydrogen,  as 
a  monovalent  element,  cannot  be  the  cause  of  it.  In  all^the 
higher  hydrocarbons  the  carbon  atoms  are  therefore  combined 
together  in  the  form  of  a  chain,  as  shown  in  the  following 
graphical  representations : — 

C  C 

C,  C,       C'C-C'C,  or  C'C;     and  so  on. 

C  C  C 

in  C2H6        in  C3H8  in  C4H10 

Various  cases  can  occur  in  the  mode  of  combination  of  the 
carbon  atoms  (Isomers).  (See  Hydrocarbons  of  the  Methane 
Series.) 

Law  Qf  Even  Numbers  of  Atoms. — The  u^   ber  of  hydrogen 


22  INTRODUCTION 

atoms  in  the  above  hydrocarbons  is  always  divisible  by  two. 
Should  they  therefore  be  partially  replaced  by  other  elements, 
the  sum  of  these  latter,  if  their  valencies  are  expressed  by  odd 
numbers,  e.g.  Cl,  N,  and  P,  and  of  the  remaining  hydrogen 
atoms  taken  together  must,  as  a  necessary  consequence  of  the 
law  of  equivalent  proportions,  remain  an  even  number. 

Radicals 

According  to  LieUg,  radicals  were  groups  of  atoms  capable 
of  a  separate  existence,  which  played  the  parts  of  elements, 
and,  like  these  latter,  could  combine  among  themselves  and  be 
exchanged  from  one  compound  to -another. 

Later  on,  the  postulate  that  such  radicals  must  also  be 
capable  of  existing  in  the  free  state  was  allowed  to  lapse,  and 
they  were  frequently  defined  shortly  as  "the  residues  left  un- 
attacked  by  certain  decompositions  ". 

Now,  however,  it  is  usual  to  designate  as  radicals  only  those 
atomic  groups  which  are  found  repeating  themselves  in  a 
comparatively  large  number  of  compounds  derived  from  one 
another,  and  which  play  in  these  compounds  the  part  of  a 
simple  element,  e.g.  CH3,  methyl;  C2H30,  acetyl;  by  this  defi- 
nition the  question  of  their  existence  or  non-existence  in  the 
free  state  does  not  arise.  The  radical  methyl,  for  example, 
is  not  known  in  the  free  state,  since,  when  its  formation 
might  be  expected,  ethane  (dimethyl),  CH3 — CH3,  is  obtained 
instead  (see  p.  37).  Such  radicals  may  be  mono-,  di-,  or  tri- 
valent,  &c.,  according  to  the  number  of  monovalent  atoms 
which  they  are  capable  either  of  replacing  or  of  combining 
with,  so  as  to  form  a  saturated  compound;  for  instance, 
(CoH4)",  ethylene,  is  divalent;  (CgHg)'",  glyceryl,  trivalent; 
(CH)'",  methine  or  methenyl,  likewise  trivalent,  &c.  The 
monovalent  residues,  CnH2n+1  (methyl,  ethyl,  &c.),  which 
form  the  radicals  of  the  monovalent  alcohols,  CJEt^OH,  are 
frequently  termed  alJcyls,  or  alphyls,  while  the  divalent  residues, 
CaHay  are  known  as  alkylenes. 

At  the  present  time  it  is  also  customary  to  speak  of  single 
atoms  as  radicals;  e.g.  we  have  the  chloride  or  iodide  radical, 
and  further,  the  hydric  radical  which  is  characteristic  of 
acids. 


CLASSIFICATION  23 

Classification  of  the  Hydrocarbons,  &c. 

The  hydrocarbons  which  have  already  been  described  are 
termed  "saturated"  compounds,  since  they  cannot  take  up 
more  hydrogen.  But  besides  these  there  are  hydrocarbons, 
&c.,  poorer  in  hydrogen,  or  "  unsaturated ",  such  as  C2H4, 
ethylene,  and  C2H2,  acetylene,  corresponding  with  which  there 
are  numerous  homologous  series. 

The  constitution  of  these  is  explained,  as  will  be  seen  later, 
by  the  assumption  of  a  double  or  triple  bond  between  neigh- 
bouring carbon  atoms,  for  instance — 

C2H4  is  written  CH2:CH^ 
CaH2  is  written  CH'CH.  • 

From  these  different  hydrocarbons,  as  starting-points,  the  most 
various  substitution  products,  such  as  alcohols,  aldehydes, 
ke tones,  acids,  amines,  &c.,  are  derived  by  exchange  of  the 
hydrogen  for  halogen,  oxygen,  nitrogen,  &c. 

To  another  class  of  hydrocarbons  belongs  that  most  impor- 
tant compound  benzene,  C6EL  which  contains  eight  atoms  of 
hydrogen  less  than  hexane,  C6H14.  With  regard  to  its  con- 
stitution, the  theory  of  the  existence  of  a  closed  chain  of  six 
carbon  atoms  has  been  advanced.  (See  Benzene  Derivatives.) 
From  benzene  are  derived  an  immense  number  of  the  most 
different  homologous  and  analogous  hydrocarbons  and  substi- 
tution products,  alcohols,  aldehydes,  acids,  and  so  on.  Thus 
benzene,  like  methane,  is  the  mother  substance  of  numerous 
organic  compounds. 

What  has  just  been  said  with  regard  to  benzene  also  holds 
good  for  various  other  compounds,  which  are  characterized  from 
a  chemical  point  of  view  by  containing  a  closed  (ring)  chain. 
These  are : — 

(a)  Trimethylene,  C3H6;  Tetramethylene,  C4H8;  and  Penta- 
methylene,  C5H10. 

(b)  Pyridine,  C5H5N,  a  strongly  basic  nitrogenous  compound, 
but  one  which  at  the  same  time  resembles  benzene  closely  in 
many  respects. 

(c)  Furane,  C4H40;    Pyrrol,   C4H5N;    Thiophene,  C4H4S; 
Pyrazole,  C3H4N2;  Thiazole,  C3H3NS;  &c. 

Some  of  these  fatter  compounds  are  extremely  like  benzene, 
others  like  pyridine ;  several  of  them  are  as  yet  only  known  in 
the  form  of  derivatives.  Like  benzene,  they  are  all  mother- 
substances  of — in  many  cases — long  series  of  compounds. 


24  INTRODUCTION 

Organic  chemistry  is  therefore  divided  into  the  following 
sections  :  — 

1.  Chemistry  of  the  Methane  Derivatives  or  Fatty  Com- 
pounds, or  Aliphatic  Compounds  (from  dAoi^,  fat),  so  called 
because  the  fats  and  many  of  their  derivatives  belong  to  this 
group.  This  section  comprises  all  carbon  compounds  with 
open  chains.  A  few  compounds,  which  are  really  closed-chain 
or  ring  compounds,  will  be  mentioned  in  this  section  on  account 
of  their  close  relationship  to  certain  open-  chain  compounds; 


as  an  example,  we  may  take  succinic  anhydride 


CH2.CO\ 


GH2 


which  is  formed  by  the  elimination  of  water  from  succinic 
acid,  OH-CO.CH2.CH2.CO.OH. 

2.  Cyclic  or  closed-cnain  compounds.     This  section  is  usu- 
ally divided  into  two  sub-sections. 

(a)  Chemistry  of  the  carbocydic  compounds,  which  comprises 
the  study  of  all  compounds  built  up  of  a  ring  of  carbon 

/~1TT 

atoms.      As    examples   we   have    •     2^>CH2,   Trimethylene  ; 

CH2' 

Tetramethylene     carboxylic     acid; 

Benzene;  &c- 

(b)  Chemistry  of  the  heterocyclic  compounds,  comprising  the 
study  of  all  ring  compounds  which  contain  other  atoms,  in 
addition  to  carbon  atoms,  as  part  of  the  ring,  e.g. 

CH.CH,  CH.CH,  OTT 

8          E 


Furane  Thiophene  Pyridine 


Physical  Properties  of  Organic  Compounds 

The  physical  properties  of  organic  compounds  are  often  of 
the  greatest  importance  for  their  characterization,  and  physical 
data  are  frequently  made  use  of  in  determining  the  purity  of 
a  chemical  compound. 

Solubility.  —  The  carbon  compounds  vary  enormously  as 
regards  their  solubility  in  various  solvents.  As  a  rule,  a 
given  solvent  dissolves  those  substances  which  are  chemically 
closely  allied  to  it.  As  example  of  this,  we  have  the  fact  that 
water  tends  to  dissolve  hydroxylic  compounds,  especially  if 


SPECIFIC  GRAVITY  25 

there  are  several  hydroxy  groups  in  the  molecule,  e.g. 
mannitol,  glucose,  and  pyrogallol. 

Benzene  tends  to  dissolve  most  hydrocarbons,  and  ether 
dissolves  the  majority  of  simple  organic  compounds,  with  the 
exception  of  salts  of  acids. 

The  usual  method  of  determining  the  solubility  of  the  given 
sjubstance  is  to  prepare  a  saturated  solution  of  the  substance  at 
the  temperature  required.  This  is  accomplished  by  one  of  two 
methods : — (a)  Shaking  the  finely-divided  solute  for  some  time 
in  contact  with  the  solvent  at  the  given  temperature,  care  being 
"taken  that  there  is  always  some  undissolved  solute  left  over. 
(b)  If  the  solute  is  more  soluble  in  hot  than  in  the  cold  solvent, 
a  concentrated  hot  solution  is  prepared,  and  is  then  allowed 
to  cool  down  to  the  temperature  required,  care  being  taken 
to  stir  the  solution  so  that  the  excess  of  solute  crystallizes 
out  and  a  supersaturated  solution  is  not  obtained.  A  known 
weight  or  volume  of  the  clear  saturated  solution  is  taken,  and 
the  solvent  removed  by  evaporation,  and  the  residual  solute 
weighed.  The  result  is  usually  expressed  in  the  form  100 
grams  of  solvent  dissolve  x  grams  of  solute  at  f . 

Specific  Gravity  and  Specific  Volume. — The  specific  gravity 
of  a  liquid  is  an  important  criterion  for  the  purity  of  the  sub- 
stance. This  is  usually  determined  in  a  specific-gravity  bottle, 
Sprengel  tube,  or  Pyknometer.  The  pyknometer  is  filled  with 
pure  water  at  a  given  temperature  (usually  4°  or  15°)  and 
carefully  weighed.  It  is  then  dried,  filled  with  the  liquid 
at  a  fixed  temperature,  and  again  weighed.  The  ratio 

w  '  °    1(^U1    is  the  specific  gravity.     It  is  usual  in  giving  the 

specific  gravity  to  denote  the  temperature  at  which  the  deter- 
mination was  made,  as  this  varies  with  the  temperature,  and 

also   the   temperature   of    the   water,   e.g.    d-^-  denotes   the 

specific  gravity  of  the  liquid  at  20°  compared  with  that  of 
water  at  4°.  The  reciprocal  of  the  specific  gravity  is  known 
as  the  specific  volume,  and  the  product  of  this  and  the  mole- 
cular weight  as  the  molecular  volume. 

Melting-Point. — Each  fusible  compound  has  a  fixed  definite 
melting-point,  and  this  constant  is  often  made  use  of  in  deter- 
mining the  purity  of  a  solid,  as  the  introduction  of  even  small 
amounts  of  impurities  lowers  the  melting-point  considerably. 
When  appreciable  amounts  of  impurities  are  present,  the 


26  INTRODUCTION 

melting-point  is  not  sharp,  but  ranges  over  a  number  of 
degrees.  The  melting-point  is  best  defined  as  the  temperature 
at  which  the  liquid  and  solid  phases  of  the  compound  are  in 
equilibrium.  The  most  direct  and  most  accurate  method  of 
determining  the  melting-point  is  to  place  a  thermometer  in 
the  molten  substance  and  allow  it  to  partially  solidify,  and 
note  the  temperature  at  which  the  mercury  remains  constant 
when  the  mixed  solid  and  liquid  is  stirred  by  the  thermometer. 
As  this  method  involves  the  use  of  a  relatively  large  amount 
of  the  substance,  the  determination  is  usually  made  by  intro- 
ducing a  very  small  amount  of  the  finely-divided  substance 
into  a  narrow  capillary  tube  closed  at  one  end.  This  tube  is 
then  attached  to  a  thermometer,  the  substance  being  at  the 
same  level  as  the  middle  of  the  bulb  of  the  thermometer,  and 
the  two  are  carefully  heated  in  a  bath  of  sulphuric  acid.  Just 
before  the  melting-point  is  reached  the  flame  is  removed  occa- 
sionally, so  that  the  temperature  rises  very  slowly,  and  the 
melting-point  can  be  read  accurately  to  within  -5  or  -25  of 
a  degree.  As  a  rule,  a  short  thermometer  is  used,  so  that  the 
whole  thread  of  mercury  is  in  the  bath,  otherwise  a  correction 
has  to  be  made  for  the  length  of  the  mercury  thread  which  is 
not  immersed  in  the  hot  bath. 

Boiling  -  Point. — The  purity  of  a  volatile  substance  can 
usually  be  determined  by  means  of  the  boiling-point,  i.e.  the 
temperature  at  which  the  vapour  pressure  of  the  substance  is 
equal  to  the  atmospheric  pressure.  It  is  usually  determined  by 
placing  the  bulb  of  the  thermometer  in  the  vapour,  and  if  a 
short  thermometer  is  employed,  and  the  whole  of  the  mercury 
thread  is  surrounded  by  the  vapour,  no  correction  is  required. 
In  each  case  the  barometric  pressure  should  be  stated,  and  also 
whether  the  thread  of  mercury  was  completely  immersed  in 
the  vapour. 

Many  substances  which  decompose  when  heated  under 
atmospheric  pressure,  may  be  distilled  without  undergoing 
decomposition  under  reduced  pressure.  This  is  accomplished 
by  attaching  the  flask,  condenser,  and  receiver  to  a  mercury 
or  water  pump  and  exhausting.  When  the  pressure  is  suffi- 
ciently reduced  the  substance  is  distilled,  care  being  taken 
that  the  pressure  under  which  the  distillation  occurs  is  mea- 
sured by  means  of  a  manometer.  As  a  rule,  considerable 
difficulty  in  avoiding  bumping  is  encountered  in  distillations 
under  diminished  pressure;  this  is  most  readily  got  over  by 
placing  a  piece  of  porous  material  (unglazed  pot)  in  the  liquid, 


STEAM  DISTILLATION  27 

or  by  slowly  aspirating  bubbles  of  air  through  the  boiling 
liquid.  (Compare  Auschutz  and  fieilter,  Brochure.  Bonn, 
1895). 

Fractional  Distillation.— Two  miscible  liquids  with  widely 
differing  boiling-points,  e.g.  alcohol,  78°,  and  aniline,  185°,  can 
be  separated  by  the  process  of  fractional  distillation,  as  the 
lower  boiling  liquid  distils  over  first.  In  all  cases  an  inter- 
mediate fraction  consisting  of  a  mixture  of  the  substances  is 
obtained,  but,  as  a  rule,  the  greater  the  difference  between  the 
boiling-points  of  the  two  substances  the  smaller  is  this  fraction. 
In  many  cases  where  the  boiling-points  are  not  very  far  re 
moved,  e.g.  benzene,  80°,  and  toluene,  111°,  the  two  compounds 
cannot  be  separated  by  a  single  fractionation;  it  is  thus  cus 
tomary  to  collect  fractions  every  5°  and  to  subject  each  oi 
these  fractions  to  further  distillation,  using  the  same  flask  for 
distillation,  and  again  collecting  every  5°.  It  is  then  found 
that  there  is  a  large  fraction  boiling  at  80-85°  and  consisting 
of  nearly  pure  benzene,  and  a  large  fraction,  110-111°,  consist- 
ing of  pure  toluene,  and  a  number  of  small  fractions  boiling  at 
85-90°,  90-95°,  &c.,  and  consisting  of  mixtures  of  benzene  and 
toluene.  The  process  is  often  quickened  by  using  some  form 
of  fractionating  column.  This  consists  of  a  long  tube  with 
bulbs  blown  on,  and  serves  to  lengthen  the  neck  of  the  flask. 
The  Linneman  tube  contains  small  wire -gauze  cups  in  the 
constricted  parts,  and  in  these  drops  of  the  higher  boiling 
liquid  collect,  and  thus  all  the  vapour  has  to  pass  through 
or  be  washed  by  these  drops.  The  same  purpose  is  served  in 
the  Glynsky  tube  by  placing  a  glass  ball  in  each  constriction. 
(See  S.  Young,  "Fractional  Distillation".  London,  1903.) 

It  is  not  always  possible  to  separate  liquids  by  fractional 
distillation,  for  example,  when  the  boiling-points  are  very 
close,  or  when  the  two  substances  form  a  mixture  of  definite 
boiling-point.  When  dilute  nitric  acid  is  distilled,  water  first 
passes  over,  and  then  a  mixture  of  water  and  nitric  acid,  until 
the  residue  in  the  flask  is  68  per  cent  nitric  acid,  and  then  it 
boils  constantly  at  126°,  since  the  vapour  and  the  liquid  in  the 
flask  have  the  same  composition. 

Mixtures  of  constant  boiling-point  are  always  characterized 
by  the  fact  that  they  have  a  vapour  pressure  either  higher  or 
lower  than  that  of  either  of  the  constituents,  or  than  that  of 
any  other  mixture  of  the  same  compounds. 

Steam  Distillation.—  This  is  the  process  frequently  resorted 
to  in  the  separation  of  a  compound  readily  volatile  in  steam 


28  INTRODUCTION 

from  other  substances,  e.g.  tars  or  inorganic  salts,  which  are 
not  volatile.  It  consists  in  blowing  steam  through  the  mixture, 
and  condensing  the  steam  and  volatile  compound  by  means  of 
a  Liebig  condenser.  Very  often  the  volatile  compound  is  prac- 
tically insoluble  in  water,  and  separates  as  an  oil  or  solid  in 
the  distillate.  The  rapidity  with  which  a  given  substance 
distils  with  steam  depends  on  the  vapour  pressure  of  the  sub- 
stance at  the  given  temperature,  and  also  on  its  molecular 
weight  or  vapour  density  compared  with  that  of  water.  Thus 
a  mixture  of  nitro-benzene  and  water,  which  may  be  regarded 
as  non-miscible  liquids,  boils  at  99°;  i.e.  the  vapour  pressure  of 
the  mixture  at  99°  is  760  mm.  The  vapour  pressure  of  water  at 
99°  is  733  mm.,  and  therefore  the  partial  pressure  of  the  nitro- 

733 
benzene  is  27  mm.    In  a  given  volume  of  the  mixed  vapours  j— 

27  . 

will  consist  of  steam  and  -£—-  of  nitro-benzene,  and  the  relative 
760 

weights  of  these  volumes  will  be  the  volumes  x  relative  den- 
sities, i.e.  9  *  733  :  61  *  27  i.e.  4 : 1;  or,  in  other  words,  Uh 
760  760 

by  weight  of  the  total  distillate  will  consist  of  nitro-benzene. 

Other  methods  very  frequently  used  in  the  purification  of 
solid  compounds  are  crystallization  and  fractional  crystalliza- 
tion. The  method  employed  is  essentially  the  same  as  that 
made  use  of  in  purifying  inorganic  compounds,  except  that 
organic  solvents,  e.g.  alcohol,  chloroform,  benzene,  carbon  disul- 
phide,  and  low -boiling  petroleums,  are  largely  used.  Often 
a  mixture  of  two  solvents  is  more  serviceable  than  a  single 
one,  e.g.  substances  are  often  crystallized  by  solution  in  warm 
alcohol  and  addition  of  water,  or  solution  in  benzene  and  addi- 
tion of  petroleum,  until  a  slight  turbidity  ensues.  The  fact 
that  a  substance  crystallizes  from  a  given  solvent  in  well- 
defined  crystals  does  not  necessarily  indicate  that  the  substance 
is  a  single  chemical  individual,  as  numerous  examples  of  mixed 
crystals  with  definite  melting-points  are  known,  and  these 
are  not  resolved  when  repeatedly  crystallized  from  the  same 
solvent. 

Extraction  with  Ether,  Benzene,  &c, — Partition  Coefficient, 
— An  organic  compound  can  often  be  separated  from  other 
substances,  especially  inorganic  salts,  by  shaking  out  with 
ether,  separating  the  ethereal  layer  by  means  of  a  separating 
funnel,  drying  the  solution  with  granular  calcium  chloride  or 
some  other  suitable  drying  agent,  and  removing  the  ether  by 


EXTRACTION   WITH  ETHER,   ETC.  29 

distillation.  The  method  gives  very  good  results  when  the 
compound  to  be  extracted  is  much  more  soluble  in  ether  than 
in  water,  and  when  the  substances  from  which  it  is  to  be 
separated  are  insoluble  in  ether.  When  there  is  no  marked 
difference  in  the  solubilities  of  the  given  compound  in  ether 
and  in  water,  the  extraction  must  be  repeated  a  number  of 
times,  in  some  cases  even  twenty,  since  for  each  compound 

.    cone,  of  ethereal  solution  . 

the  ratl°  cone,  of  aqueous  solution  ls  a  constant'  and  ls  usually 
termed  the  partition  coefficient  or  coefficient  of  distribution  of  the 
particular  substance  between  the  two  solvents.  In  extractions 
with  ether  it  must  be  borne  in  mind  that  ether  dissolves  to  an 
appreciable  extent  in  water,  and  also  water  in  ether..  Other 
liquids,  such  as  benzene,  carbon-disulphide,  chloroform,  &c., 
may  be  used  in  place  of  ether. 

When  the  amount  of  solvent  to  be  used  is  limited,  it  is 
more  economical  to  extract  two  or  three  times  with  small 
amounts  of  solvent  rather  than  only  once  with  the  whole 
amount.  As  an  illustration.  11  grams  of  a  substance  and 
1  litre  each  of  the  non-miscible  liquids,  water  and  benzene. 
The  solubility  of  the  substance  in  benzene  is  ten  times  its 
solubility  in  water,  and  it  has  the  same  molecular  weight  in 
both  solvents. 

Case  /.  —  Extracting  at  once   with  the  litre  of   benzene, 

cone,  of  benzene  solution         10  ,    , 

-  j  —    -  i—  -.  —  =  -=-,   i.e.   iVth   of   the   whole,   or 
cone,  of  water  solution  1  ' 

1  gram,  remains  in  the  water. 

Case  //.—Extract  twice  with  500  c.c.  of  benzene.  After 
first  extraction,  suppose  x  grams  passes  into  the  benzene,  then 
cone,  of  aqueous  solution  is  11  —  x,  and  of  the  benzene  2xt 

=  -y-,  or  x  =  9  (approx.),  and  2  grams  are  left 


..  - 

I  I   "™™  ' 

in  the  water. 

After  extraction  with  second  quantity  of  benzene,  y  grams 

go  into   the   benzene.      Then   ^  _       =    y,   or  y    —    1'7 

(approx.),  and  only  0'3  gram  remains  in  the  aqueous  solu- 
tion. Whereas,  after  the  single  extraction  with  a  litre  of 
benzene  1  gram  was  left. 

For  applications  of  this  method  in  determining  the  relative 
strengths  of  acids  and  amines,  compare  Farmer  and  Warth 
(J.  C.  S.  1904,  1713). 


CLASS  L— ALIPHATIC  OE  OPEN-CHAIN 
COMPOUNDS 


I.  HYDEOCAEBONS 

A.  Saturated  Hydrocarbons,  cyi^ 

This  constitutes  the  simplest  homologous  series  of  carbon 
compounds,  and  all  the  saturated  open-chain  compounds  may 
be  regarded  as  derived  from  these. 

The  following  list  includes  the  more  important  normal 
hydrocarbons : — 


Formula. 

Name. 

Melting- 
point. 

Boiling- 
point. 

Specific  gravity. 

CH4 

C2H6 

Methane 
Ethane 

—  186° 
-172° 

—164° 

-84° 

0-415  at  b.-p. 
0-446  at  0° 

cX 

Propane 

-37° 

0-536  at  0° 

C4H10 

Butane 

+1° 

0-600  at  0° 

^6-^-12 

Pentane 

37° 

0-627  at  14° 

C6H14 

Hexane 

69° 

0-658  at  20° 

C7H16 

Heptane 

98° 

0-683  at  20° 

CoHjo 

Octane 

125° 

0-702  at  20° 

n  TT 

O9±120 

Nonane 

-51° 

150° 

0-718  at  20° 

n  TT 

V-J'10X-L22 

Decane 

—  31° 

173° 

0-730  at  20° 

CnH24 

TJndecane 

-26° 

195° 

0-774  at  m.-p. 

^12^-26 

Dodecane 

-12° 

214° 

0-773  at  ni.-p. 

C14H30 

Tetradecane 

+4° 

252° 

0-775  at  m.-p. 

^16^-34 

Hexadecane 

18° 

287° 

0-775  at  m.-p. 

C2oH42 

Eicosane 

37° 

205°* 

0-778  at  m.-p. 

^21-^-44 

Heneicosane 

40° 

215°* 

0-778  at  rn.-p. 

^23^48 

Tricosane 

48° 

234°* 

0779  at  m.-p. 

C31H64 

Hentriacontane 

68° 

302°* 

0-781  at  m.-p. 

^36-^-72 

Pentatriacontane 

75° 

331°* 

0-782  at  m.-p.  ! 

r<  TT 

v^60rL122 

Hexacontane 

101° 

*  Under  16  mm.  pressure. 

The  first  members  of  the  series,  including  those  with  about 
four  atoms  of  carbon,  are  gases,  which  gradually  become  more 
easily  condensable  as  the  number  of  carbon  atoms  in  the  mole- 
cule increases.  The  members  which  follow  are  liquid  at  the 


SATURATED  HYDROCARBONS  31 

ordinary  temperature,  their  boiling-point  rising  with  increasing 
number  of  carbon  atoms.  An  increase  of  CH2  in  the  mole- 
cular formula  does  not  necessarily  denote  a  definite  increase 
in  the  boiling-point.  The  difference  in  boiling-point  between 
hexane  and  heptane  is  29°,  and  between  undecane  and  dode- 
cane  only  19°:  thus  with  compounds  of  high  molecular  weight 
an  increase  of  CH2  does  not  produce  so  marked  an  effect  on 
the  boiling-point  as  with  simpler  compounds.  The  higher 
homologues,  from  about  C16H34  (melting-point  18°)  on,  are 
solid  at  the  ordinary  temperature,  and  their  melting-point 
gradually  rises  up  to  about  100°.  The  highest  members  can  be 
distilled  under  diminished  pressure  only.  The  methane  homo- 
logues are  almost  or  quite  insoluble  in  water;  alcohol  dissolves 
the  gaseous  members  to  a  slight  extent,  the  liquid  members 
easily,  and  the  solid  with  gradually  increasing  difficulty.  Their 
specific  gravities  at  the  melting-point  increase  with  increasing 
number  of  carbon  atoms  from  0'4:  up  to  0*78,  which  is  the 
maximum  limit.  This  value  is  already  almost  reached  by  the 
hydrocarbon  CnH24,  so  that  for  the  higher  members  of  the 
series  the  following  law  holds  good:  "the  molecular  volumes 
are  proportional  to  the  molecular  weights  "  (Krafft). 

They  are  incapable  of  combining  further  with  hydrogen  or 
halogens  (see  p.  23),  and  absorb  neither  bromine  nor  sulphuric 
acid.  They  are  therefore  termed  the  Saturated  Hydro- 
carbons. Even  fuming  nitric  acid  has  little  or  no  action 
upon  the  lower  members  of  the  series;  thus,  methane  is  not 
attacked  by  a  mixture  of  fuming  nitric  and  sulphuric  acids, 
even  at  150°.  They  are  also  very  indifferent  towards  chromic 
acid  and  permanganate  of  potash  in  the  cold,*  when  oxidation 
does  take  place,  they  are  mostly  converted  directly  into  car- 
bonic acid.  The  name  of  "  The  Paraffins  "  (from  parum  affinis), 
which  was  originally  applied  only  to  the  solid  hydrocarbons 
from  lignite,  has  therefore  been  extended  to  the  whole  homo- 
logous series. 

By  the  action  of  the  halogens  (01,  Br),  substitution  takes 
place,  the  substituted  hydrogen  combining  with  an  amount  of 
halogen  equal  to  that  which  has  entered  the  hydrocarbon  (see 
Substitution  products  of  the  Hydrocarbons) : 
CH3H  +  C1C1  =  CH,C1  +  HC1. 

As  the  number  of  carbon  atoms  increases,  the  percentage 
composition  of  these  hydrocarbons  approaches  a  definite  limit, 

*  With  the  exception  of  compounds  containing  the  grouping  R'R"R"'CH. 


32 


I.   HYDROCARBONS 


viz.  that  of  the  hydrocarbons,  CnH2n,  or  CH2,  as  is  shown  by 
the  following  table : — 


Per 

cent. 

CH4 

C2H6 

C3H8 

C6HU 

C]cHs4 

C^HIS 

C^H^ 

CssHre 

Limit 
Value, 

CnHfc, 

c 

H 

i 

75-00 
25-00 

80-00 
20-00 

81-82 
18-18 

83-72 
16-28 

84-60 
15-40 

85-16 
14-84 

85-21 
14-79 

85-36 
14-64 

85-71 
14-29 

It  is  therefore  impossible  to  distinguish  by  elementary 
analysis  between  two  of  the  neighbouring  higher  homologues, 
e.g.  C22  and  C24,  C24  and  C30;  the  only  reliable  data  here  are 
the  methods  of  formation  from  compounds  in  which  the 
number  of  carbon  atoms  in  the  molecule  is  already  known, 
and  the  melting-points. 

homers.  —  Only  one  representative  each  of  the  formula! 
CH4,  C2H6,  and  C3H8  is  known,  but  of  C4H10  there  are  two, 
of  C5H12  three,  and  of  C6H14  already  five  isomers,  and  most  of 
the  higher  hydrocarbons  are  known  in  various  isomeric  forms. 
From  this  the  conclusion  is  drawn  that  in  these  different 
isomers  the  carbon  atoms  are  differently  combined,  in  the  one 
case  in  a  straight  line  without  branching,  like  the  links  of  a 
chain;  in  the  other,  with  the  formation  of  a  branching  chain. 
(This  is  of  course  not  to  be  taken  as  meaning  that  they  ar« 
grouped  together  in  space  in  straight  lines.)  Thus:  — 


or 


The  first  of  these  hydrocarbons,  with  a  non-branching  chain, 
are  termed  the  normal  hydrocarbons;  the  last,  the  iso-hydro- 
carbons. 

The  principles  by  which  such  constitutional  formulae  are 
arrived  at  will  be  explained  under  Butane  and  Pentane. 

Only  those  homologues  are  comparable  whose  constitutions 
are  similar,  as  in  the  case  of  the  normal  hydrocarbons. 

Occurrence.  —  The  hydrocarbons  of  the  paraffin  series  occur 
naturally  in  great  variety.  Thus,  methane  is  exhaled  from 
the  earth's  crust,  as  "fire-damp"  and  as  marsh-gas.  The  next 
higher  homologues  are  found  dissolved  in  petroleum,  which 
also  contains  the  higher  hydrocarbons  in  large  amount.  Solid 
hydrocarbons  occur  as  ozokerite  or  earth-wax.  By  the  frac- 
tional distillation  of  petroleum  a  large  number  of  these  com- 


MODES   OF  FORMATION  33 

pounds  have  been  isolated.  Heptane  and  hexadecane  are  also 
found  in  the  vegetable  kingdom. 

Modes  of  formation. — A.  Various  members  of  this  series  are 
obtained  by  the  distillation  of  lignite  (Boghead,  Cannel  coal), 
wood,  bituminous  shale,  and,  in  very  much  smaller  quantity, 
from  pit  coal.  Paraffins  are  also  obtained  by  dissolving  car- 
bide of  iron  in  acids,  and  by  heating  wood,  lignite,  and  coal, 
but  riot  graphite,  with  hydriodic  acid. 

B.  From  substances  containing  an  equal  number  of  carbon 
atoms  in  the  molecule. 

1.  From    the   halogen   alkyls,*   CnH2n+1X,   and,   generally 
speaking,  from  the  substitution  products  of  the  hydrocarbons 
by  exchange  of  the  halogen  for  hydrogen  (inverse  substitu- 
tion).    This  is  effected  by  the  action  of  reducing  agents,  that 
is,  agents  which  give  rise  to  nascent  hydrogen.     Some  of  the 
commoner  reducing  agents "  employed  for  such  purposes  are 
sodium  amalgam  and  water,  zinc  and  a  dilute  acid,  zinc  and 
water  at  160°,  the  copper-zinc  couple  in  presence  of  water 
and  alcohol  (Gladstone-Tribe),  aluminium-  or  magnesium-amal- 
gam and  alcohol,  and  one  of  the  most  vigorous  reducing  agents, 
concentrated  hydriodic  acid  at  high  temperatures,  especially 
in  contact  with  red  phosphorus,  which  serves  to  continually 
renew  the  hydrogen  iodide.     (See  chapter  on  Reduction.) 

2.  From  monohydric  alcohols,  CnR,^  •  OH,  polyhydric  alco- 
hols,  CnH2n(OH)2,   CJHs^OH)*   &c.,   also   from  aldehydes, 
CnHta+1'CHO,  ketones,  CnHta+1.CO«CllHan.tl,  and  other  com- 
pounds containing  oxygen,  by  heating  with  hydriodic  acid 
and  red  phosphorus  at  relatively  high  temperatures.     In  all 
these  reactions  the  oxygen  is  ultimately  removed  as  water. 

3.  From  hydrocarbons  poorer  in  hydrogen,  i.e.  unsaturated 
hydrocarbons  (see  these),  by  the  addition  of  hydrogen;  e.g. 
ethane  from  ethylene  or  acetylene  and  hydrogen,  either  in 
presence  of  platinum  black  or  finely-divided  nickel  or  by  heat- 
ing the  mixture  of  gases  to  400°-500°.     Also  by  heating  with 
hydriodic  acid  (Kraffl\  or  by  addition  of  halogen  or  halogen 
hydride,  and  exchange  of  the  halogen  for  hydrogen,  according 
to  1.     Thus:— 


=  C2H6,  f  C2H4  +  HBr     =  C3H6Br, 

C;HIO  +  2HI  =  C6H12  +  I2;     \C2H6Br  +  2H  =  C3Hfl  +  HBr. 


*  The  monovalent  residues,  CnHan.M,  methyl,  ethyl,  &c.,  which  are  at  the 
same  time  the  radicals  of  the  monohydric  alcohols,  CnHjn  +  iOH,  are  fre- 
quently termed  alkyl  groups, 

(B480)  C 


34  L   HYDROCARBONS 

4.  By  decomposing  the  organo-zinc  compounds  (zinc-alkyls) 
with  water  (Fmnkland) — 

Zn(C2H6)2  +  2H20  =  Zn(OH)2  +  2C2Hfi. 

Or  more  readily  by  decomposing  Grignard's  organo-magnesium 
compounds  with  water.  Thus  ethyl  iodide  and  magnesium,  in 
presence  of  dry  ether,  yield  ethyl  magnesium  iodide,  C2H6« 
Mg«I,  and  this  with  water  evolves  ethane: 

C2H6.Mg.I-t-H.OH  =  C2H6-f  OH-Mg.L 

C.  From  acids  containing  more  carbon,  with  separation  of 
carbon  dioxide.     Thus,  by  heating  acetate  of  calcium  with 
soda-lime,  methane  and  carbonic  acid  are  formed: 

(CH3COO)2Ca  +  Ca(OH)2  =  2CH4  +  2CaCOs. 

In  the  case  of  the  acids  of  higher  molecular  weight,  this 
separation  of  carbonic  acid  is  conveniently  effected  by  heating 
with  sodic  ethoxide. 

D.  By  the  combination  of  two  radicals  containing  a  smaller 
number  of  carbon  atoms. 

1.  By  the  action  of  sodium  upon  the  alkyl  iodides  in  ethereal 
solution  (Wurtz)\  or  by  heating  with  zinc  in  a  sealed  tube 
(Frankland): 

2  CH3I  -f  2  Na  =  C2HG  +  2  Nal. 

By  this  method  also  two  different  radicals  can  be  combined, 
e.g.  C2H5I  +  C4H9I  give  C2H5  +  C4H9  =  C6H14,  ethyl-butyl 
(Wur&s  "Mixed  Radicals"). 

2.  By  the  electrolysis  of  solutions  of  the  potassic  salts  of 
fatty  acids  (Kolbe,  1848).    The  anions,  for  example,  CH3.COO, 
when  discharged  at  the  anode,  break  up  into  CH3  and  C02, 
and  two  of  the  CH3  groups  immediately  combine  to  form  a 
molecule,  CH3  •  CH3,  viz.  ethane.    The  hydrogen  is  here  evolved 
at  the  cathode,  and  the  hydrocarbon  at  the  anode;  the  carbon 
dioxide  is  to  a  large  extent  retained  in  the  solution. 

Methane,  CH4  (Folta,  1778).  Occurrence. — As  an  exhalation 
from  the  earth's  crust,  more  especially  at  Baku  in  the  neigh- 
bourhood of  the  Caspian  Sea  (the  "Iloly  Fire"  of  Baku)j  from 
the  large  gas  wells  at  Pittsburg,  in  North  America,  and  in 
numerous  other  places;  in  the  exhalations  from  mud  volcanoes, 
for  instance  at  Bulganak  in  the  Crimea,  where  the  gas  is  almost 
pure  methane  (Bunsen);  and  as  pit  gas  or  "fire-damp"  in  mines, 
where,  when  mixed  with  air,  it  is  apt  to  cause  explosions. 

As  marsh-gas,  together  with  carbon  dioxide  and  nitrogen, 


METHANE  35 

by  the  decomposition  of  organic  substances  under  water; 
further,  by  the  fermentation  of  cellulose,  e.g.  by  river  mud, 
by  means  of  Schizomycetes  (fission-fungi). 

It  is  also  found  in  rock-salt  (the  Knistersalz  of  Wieliczka), 
and  in  the  human  intestinal  gases  (up  to  57  per  cent  CH4 
after  eating  pulse). 

The  illuminating  gas  obtained  by  the  destructive  distillation 
of  coal  contains  about  40  per  cent  methane. 

Modes  of  preparation. — 1.  Methane  is  formed  synthetically  by 
the  direct  union  of  carbon  and  hydrogen.  Pure  sugar  carbon 
freed  from  all  traces  of  hydrogen  by  treatment  with  chlorine 
is  heated  in  a  current  of  dry  hydrogen  in  a  porcelain  tube,  and 
the  issuing  gas  is  found  to  contain  one  per  cent  of  methane 
(Bonezud  Jerdan,  J.  C.  S.,  1897,  41;  1901,  1042;  Pring,  1910, 
489;  Pring  and  Fairlie,  1911,  1796,  1912,  91);  and  is  also 
formed  by  the  decomposition  of  ethane,  ethylene,  and  acety- 
lene at  moderate  temperatures  (Bone  and  Coward,  1908,  1197). 

2.  When  carbon  monoxide  and  hydrogen  are  passed  over 
reduced  nickel  at  200°-250°.     The  nickel  acts  as  a  catalytic 
agent,  and  apparently  undergoes  no  change.     Carbon  dioxide 
may  be  substituted  for  the  monoxide.    (Sabatier  and  Sender  ens.) 
The  reactions  are: — 

CO  +  3H2  =  CH4  +  H20    and    C02  +  4H2  =  CH4  +  2H20 

3.  By  leading  sulphuretted  hydrogen  and  carbon  bisulphide 
vapour  over  red-hot  copper  (Saihelot);  CS2  -f  2H2S  -f  8Cu 
=   CH4  -f  4Cu2S.      Steam  may  be  substituted  for  the  sul- 
phuretted hydrogen. 

4.  It  is  usually  prepared  by  heating  anhydrous  sodic  acetate 
with  baryta,  or,  less  advantageously,  with  soda-lime  (cf.  p.  34), 
ethylene,  C2H4,  and  hydrogen  (up  to  8  per  cent)  being  formed 
at  the  same  time. 

5.  Pure  methane  is  obtained  from  magnesium  methyl  iodide 


and  water,  CH^-Mg-I  +  H-OH  =  CH4  +  OH-Mg-I;  also 
(see  B,  1)  by  the  reduction  of  methyl  iodide,  CH3I,  e.g.  in 
alcoholic  solution  by  means  of  zinc  in  the  presence  of  pre- 

ni-rv!4ri4-<->s3    f.f\-r\-r\r\m   /±V./-k    ffl  n  J0ir\m  a^  /7T/n/7n>    "  r~!r»r»np»T»_7.Tnp.   liOlTnlft      i  t"*" 


cipitated  copper  (the  Gladstone-Tribe  "Copper-zinc  Couple"), 
also  by  the  inverse  substitution  of  chloroform,  CHCl^  or  carbon 
tetrachloride,  CC14. 

Properties.— -It  is  a  gas  with  a  dersity  =  8  (H  =  1),  and 
is  condensed  under  a  pressure  of  ^0  atmospheres  at  0°.  It 
boils  at  —164°,  and  solidifies  at  —186°.  Absorption  coefficient 
in  cold  water  about  0'05,  in  cold  alcohol  0'5.  It  burns  with  a 


36  I.   HYDROCARBONS 

pale  and  only  faintly  luminous  flame,  yielding  carbon  dioxide 
and  water,  and  when  mixed  with  air  or  oxygen  in  certain  pro- 
portions forms  an  explosive  mixture.  It  is  decomposed  by  the 
electric  spark  into  its  elements,  and  a  similar  decomposition 
occurs  when  the  gas  is  led  through  a  red-hot  tube;  but  there 
are  formed  at  the  same  time  C2H6,  C2H4,  C2H2,  and,  in  smaller 
quantity,  C6H6,  benzene,  C10H8,  naphthalene,  and  other  pro- 
ducts. The  first  three  hydrocarbons  just  mentioned,  ethane, 
&c.,  behave  similarly. 

Combustion  of  Hydrocarbons. — When  methane  and  hydro- 
carbons generally  are  burnt  or  exploded  with  excess  of  air  or 
oxygen,  the  final  products  are  carbon  dioxide  and  water  vapour, 
and  the  reaction  is  generally  represented,  e.g.,  by  the  equation 
CH4  -f  2  02  =  C02  -f  2  H20.  This  undoubtedly  represents 
the  final  products  which  are  formed,  and  also  their  relative 
amounts,  but  does  not  give  an  idea  of  the  mechanism  of  com- 
bustion. Numerous  investigators  have  conducted  experiments 
on  combustion,  especially  on  combustion  in  the  presence  of 
limited  amounts  of  oxygen.  The  conclusion  was  first  drawn 
that  with  a  defective  supply  of  oxygen  the  hydrogen  is  oxi- 
dized in  preference  to  the  carbon.  Somewhat  later,  Kersten 
(1861)  suggested  the  preferential  burning  of  the  carbon,  since 
when  ethylene  is  exploded  with  its  own  volume  of  oxygen, 
carbon  monoxide  and  hydrogen  are  the  chief  products.  (Cf. 
Smitkdls,  J.  C.  S.  1892,  61,  220.) 

The  recent  work  of  Bone  and  others  on  the  slow  combustion 
of  methane,  ethane,  ethylene,  and  acetylene  (J.  C.  S.  1902,  535; 
1903,  1074;  1904,  693,  1637;  Proc.  1905,  220;  B.  A.  Eeport, 
1910,  469),  shows  that  by  passing  a  mixture  of  methane  and 
oxygen  in  a  continuous  stream  through  a  tube  filled  with 
porous  material  (pot  or  magnesia),  at  a  fixed  temperature 
between  350°  and  500°,  appreciable  amounts  of  formaldehyde 
are  obtained.  Gaseous  products  are  also  obtained,  but  these 
are  probably  due  to  secondary  reactions,  e.g.  either  the  further 
oxidation  of  the  aldehyde  to  carbon  monoxide,  carbon  dioxide, 
and  steam,  or  the  thermal  decomposition  of  the  aldehyde  into 
carbon  monoxide  and  hydrogen.  Thus : — 

^^*CO  +  Ha  +  H20 

CH4  >  CH2(OH)a     »•  OH,  :0+HaO<C^^Thermal  decomposition 

.Oxidation     * 


CO,  4-   H2  +  H20 

Thermal  decomposition. 


ETHANE  37 

By  the  expression  thermal  decomposition  is  meant  that  at  the 
temperature  mentioned  the  aldehyde  is  unstable,  and  imme- 
diately decomposes  into  the  simpler  products,  CO  and  H2. 

Ethane  behaves  similarly,  and  the  reactions  can  be  repre- 
sented by  the  following  scheme : — 

CH3.CH3  —  CH3.CH(OH)2  -*  CH3.CH:0  + ELO  — 

oa  o, 

OH.CH2.C02H 

i 
CH2:0-hCO  +  H20. 

Secondary  reactions  are  the  thermal  decompositions  of  the 
formaldehyde  into  CO  and  H2,.  and  of  the  acetaldehyde  into 
CH4  and  CO.  In  reality  some  80  per  cent  of  the  ethane  can 
be  collected  as  formaldehyde.  With  ethylene  the  reactions 
are  probably — 

CH2:CH2  —  OH.CHrCH-OH  —  2CH2:O  —  H-CO2H  —    , 
O2  00 

OH-CO-OH, 

and  the  thermal  decomposition  products  of  the  formaldehyde, 
formic  acid,  and  carbonic  acid,  viz.  H2,  CO,  C02,  H20. 

It  is  thus  obvious  that  at  the  temperatures  mentioned  (350- 
500°)  combustion  consists  primarily  in  the  addition  of  oxygen 
and  the  production  of  hydroxylic  compounds,  which  then  yield 
aldehydes.  It  is  highly  probable  that  reactions  of  a  similar 
nature  occur  during  explosive  combination  ana  detonation  at 
high  temperatures  (B.  A.  Report,  1910,  492). 

Ethane,  C2H6,  occurs  in  crude  petroleum  and  constitutes 
the  gas  of  the  Delamater  gas  well  in  Pittsburg,  and  is  there 
utilized  for  technical  purposes. 

Preparation. — By  the  electrolysis  of  acetic  acid  (Kolbe,  1848), 
and  therefore  formerly  called  "  methyl "  since  it  was  supposed 
to  be  CH3 ;  subsequent  molecular-weight  determinations  proved 
it  to  have  the  double  formula  C2H6.  It  is  also  obtained  from, 
ethyl  iodide,  alcohol,  and  zinc  dust,  or  from  zinc  ethyl  (Frank- 
land),  hence  the  name  "ethyl  hydride".  "Ethyl  hydride"  and 
"  methyl ",  which  were  formerly  supposed  by  FranHand  and 
Kolbe  to  be  different  substances,  were  proved  to  be  identical  by 
Schorlemmer  in  1863  by  their  conversion  into  C2H5C1,  which 
may  be  prepared  from  both  in  exactly  the  same  way. 

It  is  a  gas  which  can  be  condensed  under  a  pressure  of 
46  atmospheres  at  4°,  and  is  somewhat  more  soluble  than 


88  L   HYDROCARBONS 

methane  in  water  and  alcohol.  It  burns  with  a  faintly- 
luminous  flame. 

Propane,  C3Hg,  and  the  two  butanes,  C4H10,  are  also  gaseous 
at  the  ordinary  temperature,  and  are  present  to  a  certain  ex- 
tent in  crude  petroleum. 

Theoretically  propane  can  exist  in  only  one  form,  represented 
by  the  constitutional  formula  CH3»CH2»CH3,  as  this  is  the 
only  manner  in  which  three  carbon  and  eight  hydrogen  atoms 
can  be  grouped  up  if  we  assume  that  the  carbon  atoms  are 
tetravalent  and  the  hydrogen  atoms  monovalent. 

ISOMERISM,  NOMENCLATURE,   CONSTITUTION 

To  determine  whether  the  next  homologue,  C4H10,  can 
theoretically  exist  in  more  than  one  modification,  we  can  start 

a  /3  a 

with  propane,  CH3»CH2'CH3,  and  replace  one  of  the  eight  hy- 
drogen atoms  by  "a  methyl  group.  It  is  obvious  that  we  can 
obtain  two  distinct  compounds  according  to  whether  we  re- 
place one  of  the  six  terminal  hydrogens  (a)  or  one  of  the  central 
hydrogens  (/?).  The  two  compounds  would  have  the  respective 
formulae 

CH3.CH2.CH2.CH3  and 

and  are  known  as  normal  butane  and  iso-butane  (or  trimethyl 
methane). 

Two  compounds  having  the  formula  C4H10  are  actually 
known,  and  their  constitutional  formulae  derived  from  their 
methods  of  formation  agree  with  the  two  formulae  CH3  •  CH2  • 
CH2-CH3  and  (CH3)2 :  CH  •  CH3,  as  the  ^compound  may  be 
obtained  by  the  action  of  zinc  on  ethyl  iodide,  CH3  •  CH2T, 
and  the  ^so-compound  by  the  reduction  of  tertiary  butyl  iodide, 
(CH3)2:CI.CH3. 

•  All  the  succeeding  hydrocarbons  can,  according  to  theory, 
exist  in  various  isomeric  modifications.  The  number  of  modi- 
fications possible  can  be  derived  in  exactly  the  same  manner 
as  already  described  for  the  butanes. 

As  an  example,  take  the  hydrocarbons  C5H12,  the  pentanes. 

a  /3  B  a 

Starting  with  n-butane,  CH3»CH2'CH2-CH3,  and  replacing 
one  H  atom  by  a  CH3  group,  we  can  get  either 

(1)  CH3.CHa.CH2.CH2.CH3    or    (2) 


NOMENCLATURE  3$ 

according  as  we  replace  an  H  atom  in  the  a  or  ft  position. 
Starting  from  iso-butane, 


We  can  similarly  get 
•:'•'       (3)  >CH.CH2.CHs    or    (4) 


but  formulae  (2)  and  (3)  are  identical,  and  the  three  isomerides 
possible  are  therefore  CH3.CH2-CH2.CH2.CHo,  (CHA>:CH. 
CH2.CH3  and  (CH3)2:C:(CH3)2.  Of  hydrocarbons  with  six 
carbon  atoms,  five  isomers  are  possible,  and  they  are  all  known. 
Of  the  nine  possible  heptanes,  C^H16,  the  existence  of  five  has 
already  been  proved. 

The  number  of  theoretically  possible  isomers  increases  very 
rapidly  with  the  number  of  carbon  atoms,  so  that,  according  to 
Cayley,  802  isomeric  hydrocarbons  of  the  formula  C13H28  are 
possible. 

Of  these  isomers  only  one  can  be  normal,  i.e.  can  have  a 
single  chain  of  carbon  atoms,  in  which  each  of  the  two  terminal 
carbon  atoms  is  combined  with  three  atoms  of  hydrogen,  and 
all  the  middle  ones  with  two,  according  to  the  formula,  CEL« 
(CH2)n.CH3. 

A  convenient  Nomenclature  for  the  more  complicated  paraffins 
is  arrived  at  by  making  methane  the  starting-point  for  all  of 
them,  that  carbon  atom  from  which  the  branching  chain  ema- 
nates being  considered  as  originally  belonging  to  CH4,  in  which 
the  hydrogen  atoms  are  supposed  to  be  wholly  or  partially  re- 
placed by  hydrocarbon  radicals,  thus:  — 


= 


dimethyl-ethyl-methane. 


The  names  of  the  well-known  lower  hydrocarbon  radicals 
(alkyls)  are  also  frequently  used  as  a  basis;  for  instance,  the 
group  (CH3)2CH  is  termed  isopropyl  (see  Isopropyl  Alcohol), 
hence  the  compounds: 


:  di-isopropyl. 


The  boiling-points  of  the  normal  hydrocarbons  are  alway* 


40  I.    HfJJiiOC  ARSONS 

higher  than  those  of  the  isomers;  indeed  the  boiling-point 
becomes  lowered  continuously  the  more  the  carbon  atom  chain 
is  branched,  i.e.  the  more  methyl  groups  are  gathered  together 
in  the  molecule. 

The  Constitution  of  the  higher  paraffins  can  in  most  cases  only 
be  arrived  at  with  certainty  from  their  synthetical  formation 
(e.g.  normal  butane  and  hexane),  or  from  their  chemical  rela- 
tion to  oxygenated  derivatives  whose  constitution  is  already 
known,  especially  to  the  ketones  and  acids.  (See  Ketones.) 

If,  for  instance,  by  the  action  of  PC15  upon  acetone,  for 
which  the  constitution  CH3»CO»CH3  is  proved,  the  substance 
CH3  •  CClg  •  CH3  (acetone  chloride)  be  formed,  and  this  be  then 
treated  with  zinc  methyl,  the  resulting  hydrocarbon,  a  pentane, 
will  have  the  constitution  (CH3)4C: 

=  ZnCl2  +  (CH3)2:C:(CH3),. 


As  a  second  example,  we  have  w-hexane,  which  can  be  ob- 
tained by  the  action  of  metals  upon  w-propyl  iodide,  as  repre- 
sented by  the  equation  : 

2CH3.CH2.CH2I  +  Zn  =  ZnI2 


The  system  of  nomenclature  suggested  by  the  International 
Congress  at  Geneva  is  as  follows:  —  The  normal  paraffins  re- 
tain their  present  names.  Thus  hexane  means  the  compound 
CH3  •  (CH2)4  •  CH3.  In  the  case  of  those  with  branching  chains 
the  longest  normal  chain  gives  the  name,  the  branches  being 
regarded  as  substituents,  and  the  position  of  substitution  being 
indicated  by  the  successive  numbering  of  the  atoms  of  the 
carbon  chain  (the  carbon  atom  which  is  nearest  to  the  point 
of  ramification  is  numbered  1;  should  there  be  more  than  one 
branching  —  say,  a  longer  and  a  shorter  —  then  No.  1  begins 
with  the  end  carbon  atom  which  stands  nearest  to  the  shorter 
branching).  Trimethyl-methane  is  therefore  called  2-methyl- 
propane;  dimethyl-ethyl-methane,  2-methyl-butane  ;  and  tetra- 
methyl-methane,  2  :  2-dimethyl-propane. 

The  following  paraffins  have  been  obtained  from  crude 
petroleum:  n-  and  eso-pentane,  7i-hexane  and  an  isomer,  and 
n-heptane,  all  these  being  present  in  the  so-called  "  gasoline  ", 
which  is  obtained  by  the  distillation  of  petroleum,  and  is  used 
for  carburetting  coal-gas;  further,  normal  Heptane,  n-Octane,* 
n-Nonane,  and  7i-Decane,  besides  an  isomer  of  each,  and  in 

*  The  petroleum  ether  and  ligroin  of  commerce  consist  principally  of  the 
hydrocarbons  C6H14,  C7H1G,  and  C8H18. 


PETROLEUM  41 

addition  to  these  (as  also  from  the  distillation  of  cannel  and 
Boghead  coal),  a  large  number  of  the  higher  hydrocarbons. 
In  all  probability  these  products  are  not  chemical  individuals, 
but  mixtures  of  homologues  and  isomers  standing  very  near  to 
each  other,  as  is  shown  by  a  comparison  with  the  artificially- 
prepared  normal  hydrocarbons. 

P.  Krafft  has  prepared  those  normal  hydrocarbons  from 
CnH24  to  C35H72,  which  are  mentioned  in  the  table  on  p.  30, 
from  the  acids  C^,  C14,  C16,  and  C18  of  the  acetic  acid  series 
(see  these),  for  which  the  normal  constitution,  i.e.  non-branching 
carbon  chain,  has  been  demonstrated;  and  also  from  the  ketones, 
CnH2uO,  which  are  obtained  by  subjecting  the  barium  salts  of 
these  acids  to  dry  distillation,  either  alone  or  together  with 
acetate  or  heptoate  of  calcium;  and  which,  as  a  consequence  of 
their  mode  of  formation,  yield  normal  hydrocarbons.  (See 
Ketones.)  Krafft  has  further  isolated  the  normal  hydro- 
carbons C]rH36  to  C23H48,  also  C24H50,  C26H54,  and  C^EU,  by 
subjecting  the  paraffin  obtained  from  lignite  to  fractional  dis- 
tillation in  vacua. 

These  are,  from  about  C16H34  (m.-pt.  18°)  on,  solid  at  the 
ordinary  temperature.  When  distilled  under  atmospheric 
pressure,  or  heated  with  AlBr3  +  HI,  the  higher  hydrocarbons 
partially  decompose  into  lower  ones  of  the  formulae  CJSan+a  and 
CnHto;  this  process  is  known  as  "cracking".  But  they  may 
be  distilled  in  a  vacuum,  whereby  their  boiling-points  are 
reduced  by  100°  or  more.  (See  table.) 

Petroleum,  Mineral  Oils. — These  are  probably  produced  by 
the  decomposition  of  animal  or  vegetable  organisms*  (Engler, 
C.  C.  1906,  II,  1017),  and  are  found  between  Pittsburg  and 
Lake  Erie  in  America;  between  Lake  Erie  and  Lake  Huron 
in  Canada;  in  Hanover,  Holstein,  and  Elsass  in  Germany;  in 
Boryslaw  in  Galicia;  in  the  Crimea;  in  the  Caucasus;  in 
Borneo,  &c.  The  American  oil  consists  mainly  of  paraffin 
hydrocarbons,  whereas  the  Eussian  oil  contains  large  quantities 
of  hydrocarbons  of  the  general  formula  CJl,^.  These  latter 
have  been  shown  to  be  closed- chain  compounds,  they  are 
known  as  naphthenes,  and  are  isomeric  with  the  olefines. 

The  American  and  Russian  oils  are  worked  up  on  a  large 
scale  for  the  preparation  of  commercial  products.  The  crude 
petroleum  is  a  thick,  oily  liquid  of  dark  colour  and  sp.  gr.  0'8 
to  0-92.  It  is  usually  washed  with  alkalis  and  sulphuric  acid, 

*  This  view  is  supported  by  the  fact  that  many  paraffin  oils  have  a  slight 
optical  activity. 


42  I.   HYDROCARBONS 

and  then  subjected  to  fractional  distillation.  The  fraction 
50-60°  is  termed  petroleum  ether  or  petrol,  the  fraction  70-90° 
is  termed  benzoline  or  benzine,  ligroin  is  the  fraction  90-120°. 
Burning  oil  is  the  fraction  150-300°,  and  from  the  higher  frac- 
tions are  obtained  lubricating  oils,  vaseline,  and  paraffin-wax. 

Paraffin- Wax,  obtained  by  Eeichenbach  in  1830  from  wood 
tar,  is  got  by  the  distillation  of  lignite  or  peat.  It  also  is  a 
mixture  of  many  hydrocarbons,  about  40  per  cent  of  it  con- 
sisting of  the  compounds  C22H46,  C24H50,  CggH^,  and  C28H58. 

Liquid  Paraffin  (Reichenbach's  "  Eupion  ")  and  the  butter-like 
Vaseline  are  high -boiling  distillation  products  of  lignite  or 
petroleum,  and  the  same  applies  to  many  lubricating  oils. 

Ozokerite,  green,  brown,  and  red,  and  of  the  consistency  of 
wax,  melting-point  60°-80°,  is  a  natural  paraffin  found  at 
Boryslaw  in  Galicia,  at  Tscheleken  near  Baku  (also  called 
Neftgil),  on  the  Caspian  Sea,  and  forms  the  ceresine  of  com- 
merce when  bleached. 

Asphalt,  or  Earth  Pitch,  found  in  India,  Trinidad,  Java, 
and  Cuba,  is  a  transformation  product  of  the  higher-boiling 
mineral-oils,  produced  by  the  action  of  the  oxygen  of  the  air 
just  as  paraffin  absorbs  oxygen  and  becomes  brown  upon  pro- 
longed heating  in  the  air.  It  is  used  for  cements  and  salves, 
and  in  asphalting,  photo-lithography,  &c. 

B.  defines  OP  Hydrocarbons  of  the  Ethylene 
Series  (Alkylenes):  CJI^ 

There  are  two  series  of  hydrocarbons  of  the  general  formula 
CnHan,  the  members  of  which  differ  from  the  corresponding 
paraffins  by  containing  two  atoms  of  hydrogen  less  in  the 
molecule.  The  one  series  is  that  of  the  Olefines,  of  which 
ethylene,  C<>H4,  is  the  first  member;  the  other  is  that  which 
contains  Trimethylene,  Tetramethylene,  Hexamethylene,  &c. 
(Cf.  Polymethylenes.) 

The  properties  exhibited  by  these  two  series  are  so  different 
that  different  constitutions  must  be  accorded  to  them.  The 
olefmes  form  additive  compounds  with  exceptional  facility, 
being  thus  converted  into  the  paraffins  or  their  derivatives; 
from  this  the  conclusion  is  drawn  that,  like  the  latter,  they 
contain  an  open  carbon  chain. 

The  names  given  to  the  hydrocarbons  are  similar  to  those 
for  the  paraffins,  except  that  the  termination  ane  is  replaced  by 
ene,  or  often  by  yUne. 


OLEFINES 
SUMMAKY 


43 


Melting-point. 

Boiling-point. 

Ethylene  

CUL 

169° 

—  .10*?° 

Propylene  

CH 

48° 

Butylene  (3>:  

fa 
G.HJ  8 

-5° 

4-1° 

Amylene  (5)         ... 

17 
C,Hin* 

-6° 
_|_39° 

OK 

68° 

Heptylene  . 

QK° 

Octylene  

§E£ 

124° 

Nonylene  

CalLo 

153° 

Decylene..    .. 

r  H 

172° 

TJndecylene  .  .  .  .        

CJI™ 

195° 

Dodecylene 

—31° 

{96°t 

Tridecylene  .                 .  . 

§32I22j 

233° 

Tetradecylen  e  

—  12° 

{127° 

Pentadecylene      ..  . 

0    FT 

247° 

Hexadecylene  (Cetene).. 
Octadecylene  .  .  . 

CicHga 
C18H,, 

+4° 
18° 

/  274° 
\{155° 
(179° 

Eicosylene  

P18rf3n 

Cerotene  

tiX 

58° 

Melene  .  . 

62° 

The  general  formula  CnH2n  for  this  series  indicates  that  each 
member  differs  from  the  corresponding  member  of  the  paraffins 
by  two  hydrogen  atoms. 

In  their  physical  properties  they  resemble  the  methane 
homologues  very  closely.  C2H4,  C3H6,  and  C^Hg  are  gases, 
C5H10  a  volatile  liquid,  the  higher  members  liquids  with  rising 
boiling-point  and  diminishing  mobility,  while  the  highest  are 
solid  and  similar  to  paraffins.  The  boiling-points  of  members 
of  both  series  containing  the  same  number  of  carbon  atoms, 
and  whose  constitutions  are  comparable,  lie  very  close  together, 
but  the  melting-points  of  the  olefines  are  somewhat  the  lower 
of  the  two;  e.g.  C]6H,4,  m.-pt.  21°,  b.-pt.  {157°,  and  C16H32, 
m.-pt.  4°,  b.-pt.  {155°.  ° 

*  The  melting-  and  boiling-points  given  from  C5Hi0  on,  are  those  of  the 
normal  hydrocarbons, 
t  {  signifies  boiling-point  under  15  mm.  pressure. 


44  I.    HYDROCARBONS 

Most  of  the  olefines  are  readily  soluble  in  alcohol  and  ether, 
but  insoluble  in  water,  only  the  lower  members  dissolving 
slightly  in  the  latter.  The  specific  gravities  of  the  normal 
olefines,  determined  at  the  melting-points,  rise  from  about  O63 
upwards,  and  approach  with  increasing  carbon  to  a  definite 
limit,  viz.  about  0'79. 

In  their  chemical  relations,  the  olefines  differ  materially  from 
the  paraffins.  Most  of  their  special  chemical  characteristics 
are  undoubtedly  due  to  the  presence  of  a  double  or  olefine 
bond  in  the  molecule,  e.g.  ethylene,  CH2:CH2.  (Cf.  Con- 
stitution of  Olefines.) 

(a)  They  combine  readily  with  nascent  hydrogen,  with 
chlorine,  bromine,  iodine,  and  their  hydracids,  fuming  sul- 
phuric acid,  hypochlorous  acid,  nitrous  acid,  and,  generally 
speaking,  with  two  monad  atoms  or  monovalent  groups, 
whereby  members  of  the  methane  series  or  their  derivatives 
ensue;  hence  their  name  of  " Unsaturated  Hydrocarbons". 


- as- 

=  C2H6(S04H). 

In  the  formation  of  these  additive  compounds  the  double 
bond  present  in  the  molecule  becomes  converted  into  a  single 
bond,  and  the  two  monovalent  groups  (e.g.  Br,  H,.OH,  &c.)  add 
themselves  on  to  the  two  carbon  atoms  between  which  the 
double  bond  previously  functionated,  e.g.  CH2:CH2  +  Br2 
gives  CH2Br'CH2Br.  Thus  by  the  addition  of  bromine  to  an 
olefine  the  two  bromine  atoms  must  always  be  attached  to  two 
adjacent  carbon  atoms.  (Cf.  Polymethylene  Hydrocarbons.) 

Combination  with  hydrogen  is  sometimes  effected,  e.g.  in 
the  case  of  ethylene,  by  the  aid  of  platinum  black  at  the 
ordinary  temperature,  by  means  of  finely-divided  nickel  at 
a  higher  temperature,  or  by  heating  the  olefines  or  their 
dichlor-,  &c.,  additive  products  with  fuming  hydriodic  acid 
and  phosphorus.  (Cf.  Modes  of  Formation  of  the  Saturated 
Hydrocarbons.) 

Ethylene  chloride,  C2H4C12,  obtained  by  the  combination 
of  ethylene  with  chlorine,  was  formerly  called  the  oil  of  the 
Dutch  chemists,  hence  the  name  of  "Olefines"  for  the  whole 
class  of  hydrocarbons  CnH2n  (Guthrie). 

Chlorine  adds  itself  on  more  easily  than  iodine,  but  hydro- 
chloric acid  less  readily  than  hydriodic,  bromine  and  hydro- 


MODES   OF  FORMATION  45 

bromic  acid  standing  midway.     When  a  halogen  hydride  is 

used,  the  halogen  attaches  itself  to  that  carbon  atom  to  which 

the  smaller  number  of  hydrogen  atoms  are  already  united,  *e.g. 

CH3.CH:CH2  +  HI  =  CH3.CHI.CH3. 

Particular  olefines,  e.g.  isobutylene,  also  combine  slowly  with 
water  to  alcohols  under  the  influence  of  dilute  acids. 

Ethylene  combines  with  fuming  sulphuric  acid  at  the  ordinary 
temperature,  and  with  the  concentrated  acid  at  160°-170°. 

Amylene  forms  with  nitrogen  tetroxide,  N204,  amylene 
nitrosate  (A.  248,  161);  nitrogen  trioxide  and  nitrosyl  chloride 
also  unite  directly  with  the  olefines. 

(b)  They  readily  polymerize,  especially  in  presence  of  sul- 
phuric acid  or  zinc  chloride.   "Thus  amylene,  C5H10,  in  presence 
of  sulphuric  acid  yields  the  polymers  C10H20,  C,§H30,  and  C20H40; 
and  tertiary  butyl  alcohol,  warmed  with  acid  of  a  definite 
strength,  di-isobutylene. 

(c)  Unlike  the  paraffins,  they  are  readily  oxidized  by  KMn04 
or  Cr03,  but  not  by  cold  HN03. 

In  this  reaction,  two  hydroxyl  groups  are  added  to  the 
molecule  of  the  olefine  if  a  dilute  (1  per  cent)  solution  of  'per- 
manganate is  used,  and  a  dihydric  alcohol  (a  glycol)  is  formed. 
CH2:CH2  T*  OH.CH2.CH2.OH. 

But  if  stronger  solutions  are  used,  or  if  chromic  anhydride  is 
employed,  the  molecule  of  the  olefine  is  ruptured  at  the  point 
where  the  double  bond  exists  and  a  mixture  of  simpler  acids 
or  ketones  is  obtained.  The  readiness  with  which  unsaturated 
compounds  discharge  the  colour  of  acidified  permanganate  is 
frequently  made  use  of  as  a  qualitative  test  for  such  compounds. 

The  "official  name"  (p.  40)  of  the  olefines  is  formed  by 
replacing  the  last  syllable  "  ane  "  of  the  paraffins  by  "  ene  ". 
The  position  of  the  double  bond  is  denoted  by  the  number  of 
the  carbon  atom  from  which  it  proceeds.  In  a  branching 
chain  the  numbering  is  the  same  as  in  the  case  of  the  corre- 
sponding saturated  hydrocarbons;  in  a  normal  chain  it  begins 
at  the  end  carbon  atom  which  is  nearest  to  the  double  bond. 

Example:     *       2      8      *        » 

is  4-methyl-2-pentene. 


Modes  of  formation.  —  (a)  Together  with   paraffins  by  the 
destructive   distillation  of   many  substances,  such   as   wood, 

*Cf.  Michael,  J.  pr.  1888,  [ii]  37,  524;  1903,  68,  487;  B.  1906,  39,  2138, 


46  I.   HYDROCARBONS 

lignite,  and  coal,  and  also  by  the  distillation  of  the  higher 
paraffins  (process  of  "cracking",  p.  41);  illuminating  gas  con- 
sequently contains  the  olefines  C2H4,  C8H6,  C4H8,  &c. 

(b)  By  abstraction  of  water  from  the  alcohols,  CnH^^OH, 
by  heating  them  with  sulphuric  acid,  phosphorus  pentoxide, 
zinc  chloride,  anhydrous  formic  acid,  syrupy  phosphoric  acid, 
&c.     When  sulphuric  acid  is  used,  an  alkyl-sulphuric  acid,  e.g. 
ethyl  hydrogen  sulphate,  C2H50  •  S02  •  OH,  is  first  formed,  and 
this  decomposes  upon  further  warming  into  alkylene  and  sul- 
phuric acid.     This  method  is  especially  applicable  in  the  case 
of  the  lower  homologues.     Many  alcohols  yield  olefines  when 
heated  alone,  or  with  finely  divided  solids  (Chap.  XLIX). 

The  palmitic  esters  of  the  higher  alcohols,  when  distilled 
under  somewhat  diminished  pressure,  yield  palmitic  acid  and 
an  olefine. 

(c)  By  heating  the  halogen  compounds  CnH2n+1X  with  alco- 
holic potash,  or  by  passing  their  vapour  over  red-hot  lime  or 
hot  oxide  of  lead,  &c.  ;  sometimes  by  simple  distillation  : 

C6HnI  +  KOH  =  C6H10  +  KI  +  H20. 

The  iodine  and  bromine  compounds  are  particularly  suited 
for  this.  The  reaction  may  be  regarded  as  the  elimination  of  a 
molecule  of  halogen  hydracid  from  the  molecule  of  the  com- 
pound, the  halogen  coming  from  the  one  carbon  atom  and  the 
hydrogen  from  an  adjacent.  (Cf.  also  Nef,  A.  1901,  318,  3.) 

(d)  Sometimes  from  the  haloid  compounds  CnH^X,  by  ab- 
straction of  the  halogen,*  e.g.  ethylene  from  ethylene  bromide 
by  treatment  with  zinc,  magnesium,  or  zinc  dust  and  alcohol: 

C2H4Br2  +  Zn  =  C2H4  +  ZnBr2. 

(e)  By  the  electrolysis  of  potassic  salts  of  dibasic  acids  01 
the  succinic  acid  series;  thus  succinic  acid  itself  yields  ethy- 
lene: 

C2H4(COOH)2  =  C2H4  +  2C02  +  H2. 

The  complex  anion  0  •  CO  •  CH2  •  CH2  •  CO  •  0,  when  discharged 
decomposes  into  ethylene  and  carbon  dioxide. 

Constitution  of  the  Olefines.  —  For  ethylene  the  following  for 
mulae  may  be  given:  — 

CH3  CH2-  CH2 


*  Only  when  the  halogen  atoms  are  attached  to  adjacent  carbon  at*#is. 


]]       METHYLENE     U  47 

.  ^_^v  ft  t*W        1^0^ 

In  the  formulae  I  and  II,  two  free  carbon  bonds  or  valencies 
are  assumed  in  the  ethylene  molecule.  Formula  III  follows 
from  the  assumption  that  the  bonds  which  are  not  used  up  in 
attaching  the  hydrogen  atoms  to  carbon  are  used  in  uniting 
the  carbon  atoms  themselves. 

Now  the  ethylene  bromide  which  is  formed  by  the  addition 
of  bromine  to  ethylene  has,  for  reasons  which  will  be  given 
under  that  compound,  the  constitution  CH2Br«CH2Br,  and 
likewise  the  compound  obtained  by  the  addition  of  C10H 
(i.e.  Cl  and  OH),  viz.  glycol  chlorhydrin,  the  constitution 
CH2C1»CH2OH;  consequently  formula  I,  according  to  which 
these  substances  would  have  the  constitutions  CH3»CHBr2 
and  CH8.CHC1(OH),  is  excluded. 

Formula  III  is  more  probable  than  formula  II: — 

(a)  Since   methylene,    CH2:,   appears  to  be  incapable   of 
existence;  all  attempts  to  isolate  it  have  yielded  ethylene, 
C2H4  (see  below),  so  that  free  valencies  attached  to  the  carbon 
atom  probably  cannot  exist. 

(b)  Because  the  free  affinities  to  be  assumed  according  to  II 
are  never  found  singly  (which  should  in  that  case  be  possible), 
but  invariably  in  pairs  only,  and  indeed  only  on  neighbouring 
carbon  atoms.     This  is  proved  from  the  constitution  of  the 
compounds   obtained   by  the  addition,  for  instance,  of   Br2. 
Unsaturated   compounds   containing   only  one  carbon   atom, 
and  unsaturated  hydrocarbons  containing  an  odd  number  of 
hydrogen  atoms,  are  unknown. 

It  is  therefore  to  be  concluded  that  in  ethylene  and  its 
homologues  a  double  carbon  bond,  corresponding  with  formula 
III,  exists. 

By  this  term  "  double  bond  "  is  not,  however,  to  be  under- 
stood a  closer  or  more  intimate  combination.  The  defines,  on 
the  contrary,  are  more  readily  oxidized  than  the  paraffins, 
being  thereby  attacked  at  the  point  of  the  double  bond. 
Other  properties,  especially  physical  ones,  also  give  indications 
that  a  double  bond  between  two  carbon  atoms  is  looser,  and 
therefore  more  easily  broken,  than  a  single  one.  (Cf.  Bruhl, 
A.  211,  162.) 

1.  Methylene  (Methene),  CH2,  does  not  exist.  Numerous 
attempts  to  prepare  it,  e.g.  by  the  withdrawal  of  hydrogen  and 
chlorine  from  methyl  chloride,  or  of  iodine  from  methylene 
jodide,  have  invariably  yielded  ethylene,  thus: — 

2CH3C1  -2HC1  =  C2H4. 

/       \~\  ^"Nl 

.*•    -  z-» 


48  I.   HYDROCARBONS 

Here  the  two  resulting  CH2-residues  have  united  together,  in 
the  same  way  as  the  two  methyl-groups  coalesced  to  ethane 
(p.  34). 

2.  Ethylene  (Ethene),  olefiant  gas,  CH2:CH2. 

This  compound  was  discovered  in  1795  by  four  Dutch 
chemists.  Its  formula  was  established  by  Dalton. 

Illuminating  gas  generally  contains  4  to  5  per  cent  of  ethy- 
lene.  For  formation  from  elements  see  Pring  and  Fairlie, 
J.  C.  S.  1911,  99,  1806.  It  is  usually  prepared  by  heating 
alcohol  with  excess  of  concentrated  sulphuric  acid,  with  addi- 
tion of  sand,  a  mixture  of  equal  portions  of  the  two  liquids 
being  subsequently  dropped  into  the  evolution  flask;  sulphur 
dioxide,  &c.,  are  produced  at  the  same  time  by  secondary  re- 
actions. A  better  method  is  to  heat  alcohol  with  syrupy 
phosphoric  acid  at  200°  (Newtli).  Small  quantities  can  be 
conveniently  prepared  from  ethylene  bromide  and  zinc  or 
magnesium.  It  is  further  formed  by  heating  ethylidene 
chloride,  CH3-CHC12,  with  sodium. 

It  may  be  liquefied  at  0°  under  a  pressure  of  44  atmos., 
is  very  slightly  soluble  in  water  and  alcohol;  burns  with  a 
luminous  flame,  and  forms  an  explosive  mixture  with  oxygen. 
When  rapidly  mixed  with  two  volumes  of  chlorine  and  set  fire 
to,  it  burns  with  a  dark-red  flame,  with  formation  of  hydro- 
chloric acid  and  deposition  of  much  soot.  It  is  converted  at 
a  red  heat  into  methane,  CH4,  ethane,  C2H6,  acetylene,  C2H2, 
&c.,  with  separation  of  carbon.  (See  p.  36.)  It  combine! 
with  hydrogen  in  presence  of  spongy  platinum  to  ethane, 
C2H6.  " 

3.  Propylene   (Propene),   C3H6,  CH2:CH-CH3.     Only  one 
olefine,  C3H6,  is  theoretically  possible  and  only  one  is  known, 
viz.  methylethylene.    It  can  be  prepared  from  isopropyl  iodide 
and  caustic  potash,  or  by  heating  glycerol  with  zinc  dust.     It 
is  isomeric  with  trimethylene  (see  Polymethylenes). 

4.  Butylene,  C4H8.     Three  butylenes  are  possible  according 
to  theory,  and  three  are  known.     All  of  them  are  gaseous, 
their  boiling-points  lying  between  —6°  and  +3°.     Butylene 
and  pseudo-butylene  are  derived  from  normal  butane,  and  iso- 
butylene  from  isobutane,  since  they  severally  combine  with  H2 
to  form  these  hydrocarbons.    The  first,  a-butylene,  is  prepared 
from  normal;  the  second,  /3-butylene,  from  secondary;  and  the 
third,  y-butylene,  from  tertiary  butyl  iodide,  by  the  action  of 
caustic  potash  upon  these;  the  last  can  also  be  obtained  from 
isobutyl  alcohol  and  sulphuric  acid.    The  isomerism  of  the  two 


V 'a 

ACETYLENE   HYDROCARBONS  49 

butylenes  derived  from  normal  butane  is  explained  by  the 
assumption  of  a  double  bond  at  different  points,  thus:— 

CH2 :  CH .  CH2  •  CH3  CH3  •  CH :  CH  •  CH3 

a-butylene  (l-butene)  /3-butylene  (2-butene). 

Isobutylene  has  the  formula  (CH3)2C :  CH2  (methylpropene).  The 
behaviour  of  these  isomers  upon  oxidation  is  in  accordance 
with  the  above  formulae,  the  oxidation  always  taking  place  at 
the  point  of  the  double  bond. 

The  butylenes  are  isomeric  with  tetra-methylene  (cydo- 
butane,  see  Polymethylenes). 

5.  Amylene,  C5H10.  A  large  number  of  isomeric  amylenes 
are  known,  among  them  being  Amylene  (b.-pt.  35°),  which  is 
obtained,  together  with  an  isomer,  Iso-amylene,  by  heating 
ordinary  amyl  alcohol  with  chloride  of  zinc.  For  it  the  con- 
stitutional formula  (CH3)2C :  CH  •  CH3  ( =  trimethylethylene)  is 
assumed.  This  is  known  in  the  pure  form  under  the  name  of 
"pental". 

The  higher  defines  of  normal  constitution,  with  12,  14,  16, 
and  18  atoms  of  carbon,  have  been  prepared  by  Kraft  accord- 
ing to  method  b. 

Cerotene  and  Melene  (m.-pt.  62°)  are  obtained  by  the  distil- 
lation of  Chinese  wax  and  bees'- wax  respectively.  They  are  like 
paraffin  in  appearance,  and  are  only  sparingly  soluble  in  alcohol. 

C.  Hydrocarbons,  CnH2n_2:  Acetylene  Series 

The  hydrocarbons  of  this  series  again  differ  from  those  of 
the  preceding  by  containing  two  atoms  of  hydrogen  less.  In 
physical  properties  they  closely  resemble  both  the  latter  and 
those  of  the  methane  series;  thus  the  lowest  members  up  to 
C,H6  are  gaseous,  the  middle  ones  liquid,  and  the  highest 
solid,  and  in  their  melting-  and  boiling-points  they  do  not 
differ  to  any  extent  from  those  of  the  other  series  with  an 
equal  number  of  carbon  atoms.  The  specific  gravities  of  the 
normal  hydrocarbons  C12,  C14,  C16,  and  C18,  at  the  melting- 
point,  gradually  approach  with  increasing  carbon  to  a  definite 
limit  (0-80),  and  are  somewhat  higher  than  those  of  the  corre- 
sponding members  of  the  ethylene  series  throughout.  ^ 

Constitution.—  Upon  grounds  similar  to  those  which  have 
already  been  explained  under  ethylene,  the  constitutional  for- 
mula for  acetylene,  C2H2,  is  assumed  to  be  CH-CH,  according 
to  which  the  carbon  atoms  are  joined  together  by  a  triple  bond. 

(  B  480  )  P 


50  I.   HYDROCARBONS 

For  a  compound  C3H4,  the  two  following  constitutional  for- 
mulae are  possible : — 

CH :  C  •  CH3  (allylene)    and    CH2 :  C :  CH2  (allene). 

As  a  matter  of  fact,  two  hydrocarbons  C3H4  do  exist,  only  one 
of  which,  allylene,  yields  metallic  compounds.  It  is  therefore 
to  be  considered  the  true  homologue  of  acetylene,  containing  a 
triple  bond,  according  to  the  first  of  the  two  above  formulae, 
while  to  allene  the  second  formula,  with  the  two  double  bonds, 
is  to  be  ascribed.  The  constitution  of  the  tetrabromopropanes, 
which  are  formed  from  these  by  the  addition  of  bromine,  agrees 
with  this  conception. 

In  their  chemical  relations  the  acetylenes  stand  nearer  to 
the  olefines  than  to  the  paraffins,  in  so  far  that  they  are  un- 
saturated  and  therefore  capable  of  forming  additive  products. 

1.  A  molecule  of  an  acetylene  can  combine  either  (a)  with 
two  atoms  of  hydrogen  or  halogen,  or  with  one  molecule  of 
halogen  hydride,  to  olefines  or  their  substitution  products, 
thus : — 

CH:CH  +  2H    =  CH2:CH2 

CHiCH  +  HBr  =  CH2:CHBr  (vinyl  bromide) 

CH:CH  +  Br2     =  CHBnCHBr;    ' 

or  (b)  with  four  atoms  of  hydrogen  or  halogen,  or  two  mole- 
cules of  halogen  hydride,  to  paraffins  or  paraffin  substitution 
products,  thus: — 

CH3.C:CH  +  4H     =  CH3.CH2.CH3 

(in  presence  of  platinum  black) 
CH :  CH  +  2  Br,        =  CHBr2  •  CHBr2 
CH3-C:CH  +  2"HI  =  CH3.CI2.CH3. 

Like  many  of  the  olefines,  various  members  of  this  series 
combine  with  water  under  the  influence  of  dilute  acids,  thus 
allylene,  C3H4,  gives  acetone,  C3H60;  and  acetylene,  C2H2, 
gives  crotonic  aldehyde,  with  intermediate  formation  of  acetic 
aldehyde.  The  combination  with  water  may  be  accomplished 
(a)  by  the  action  of  sulphuric  acid  when,  as  in  the  case  of  the 
olefines,  alkyl  hydrogen  sulphates  are  formed  as  intermediate 
products;  (b)  by  means  of  mercuric  chloride  solution;  or  (c)  by 
directly  heating  the  hydrocarbon  with  water  at  300°  in  sealed 
tubes.  HgCl2  and  other  mercury  salts  also  induce  such  hy- 
dration : 

CH:CH-fH2O        =  CH3.CHO 
CH3-C:CH  +  OH2  =  CH3.CO-CH3. 


FORMATION   OF  ACETYLENE  HYDROCARBONS  51 

2.  Many  of  the  acetylene  hydrocarbons  are  readily  poly- 
merized;  thus,  acetylene  is  transformed  into  benzene  when 
led  through  a  red-hot  glass  tube.     This  is  an  important  syn- 
thesis of  benzene: 

3C2H2  =  CJH,. 

At  the  same  time  the  compounds  C8H8,  010H8,  &c.,  are 
formed.  Similarly  allylene,  C3H4,  gives  mesitylene,  C9Hi2, 
in  contact  with  sulphuric  acid  and  a  little  water.  (See  Ben- 
zene Derivatives.) 

3.  Acetylene  and  some  of  its  homologues  react  even  at  the 
ordinary  temperature,  in  a  manner  which  is  peculiar  to  them, 
with  an  ammoniacal  solution  of  cuprous  or  argentic  oxide,  to 
form  reddish  -  brown  or  yellow-white  precipitates,  e.g.  CCu: 
CCu;  CAgiCAg;  CH3«C:CAg,  &c.,  which  are  explosive,  and 
which  are  decomposed  by  acids,  such  as  HC1,  with  regeneration 
of  the  hydrocarbon. 

The  hydrogen  of  acetylene  can  be  replaced  by  potassium  or 
sodium;  thus,  when  the  hydrocarbon  is  heated  with  sodium, 
the  compounds  C2HNa  and  C2Na2  are  obtained.  These  are 
decomposed  by  water  or  acids  with  evolution  of  acetylene. 

All  the  hydrocarbons  CJE^^  do  not,  however,  give  such 
metallic  compounds,  but  only  the  true  homologues  of  acetylene 
containing  the  grouping  •  C :  CH. 

Hydrocarbons  such  as  allene,  CH2:C:CH2,  which  do  not 
contain  a  triple  bond,  and  even  acetylene  compounds  such  as 
CH3  •  C  •  C  •  CH3,  where  no  hydrogen  atoms  are  attached  to  the 
C  atoms  between  which  the  triple  bond  is  supposed  to  exist, 
do  not  yield  these  metallic  derivatives. 

In  the  case  of  the  higher  homologues,  isomerism  may  be 
due  either  to  the  difference  in  position  of  the  triple  carbon 
bond  in  the  molecule,  or  to  the  presence  and  different  positions 
of  the  two  double  bonds.  The  constitution  of  a  compound 
is  fixed  by  the  formation  or  otherwise  of  metallic  derivatives, 
and  by  its  behaviour  upon  oxidation.  (See  Oxidation  of  the 
Butylenes,  p.  49.) 

The  official  name  of  the  acetylene  homologues  proper,  with 
a  triple  carbon-linking,  ends  in  "ine";  that  of  the  isomeric 
hydrocarbons,  with  two  double  bonds,  in  "diene". 

Formation. — 1.  They  are  obtained,  together  with  the  hydro- 
carbons already  described,  by  the  distillation  of  wood,  lignite, 
coal,  &c.;  thus  illuminating  gas  contains  acetylene,  allylene, 
and  crotonylene. 


52  I.   HYDROCARBONS 

2.  By   treating  the  haloid,  preferably  the  bromine,  com- 
pounds CnH2nX2  and  CyB^^X  with  alcoholic  potash  or  sodium 
ethoxide  (C2H5ONa): 

H\        /Br 

H^C-Cr-H  —  2HBr  =  H»C:C»H. 

Br/          \H 

With  alcoholic  potash,  even  when  excess  is  used,  the  re- 
action tends  to  stop  at  the  first  stage,  and  a  brominated  olefine 
is  formed,  e.g.  vinyl  bromide  (p.  65)  from  ethylene  dibromide; 
with  sodic  ethoxide,  the  elimination  of  hydric  bromide  pro- 
ceeds more  readily. 

Further,  from  the  unsaturated  alcohols,  CJE^^'OH,  by  the 
separation  of  the  elements  of  water  from  them. 

3.  By  the  electrolysis  of  potassium  salts  of  the  acids  of  the 
fumaric  acid  series  (KekuU). 

4.  Certain    acetylene    hydrocarbons,    R-CiC-CH3,    when 
heated  with  sodium,  pass  into  the  sodium  compounds  of  their 
isomers,  R-CH2»C:CH;  on  the  other  hand,  when  the  latter 
are  warmed  with  alcoholic  potash,  the  opposite  reaction  takes 
place  (Faworsky,  B.  20,  Ref.  781;  25,  Ref.  81;  25,  2244). 

Acetylene  (Bibine),  C2H2,  was  first  obtained  impure  by 
E.  Davy  from  calcium  carbide  in  1839,  and  pure  by  Berthelot 
in  1849.  Illuminating  gas  contains  0'06  per  cent.  It  is  syn- 
thesised  from  its  elements,  when  an  electric  arc  is  caused  to 
pass  between  two  carbon  poles  in  an  atmosphere  of  hydrogen 
(Berthelot),  but  other  hydrocarbons  are  formed  at  the  same 
time  (Bone  and  Jerdan,  J.  C.  S.  1901,  1042;  cf.  also  Button 
and  Pring,  1906,  1591).  It  may  be  obtained  from  ethylene 
bromide  and  sodium  ethoxide  solution ;  also  by  the  incomplete 
combustion  of  many  carbon  compounds,  for  instance,  when  the 
gas  in  a  Bunsen  lamp  burns  at  the  base;  and  from  ethane, 
ethylene,  and  methane  at  a  red  heat,  or  by  the  action  of  the 
induction  spark.  (See  pp.  36  and  48.)  The  simplest  method 
of  preparation  is  by  the  action  of  water  on  calcium  carbide, 
the  water  being  allowed  to  drop  gradually  on  to  the  carbide : 

•  C2H2. 


It  becomes  liquid  at  1°  under  a  pressure  of  48  atmospheres, 
burns  with  a  luminous  and  very  sooty  flame,  and  has  a  peculiar 
disagreeable  smell.  Its  flame  has  a  high  illuminating  power- 
when  burnt  in  specially-constructed  burners,  and  is  now  largely 
made  use  of  as  an  illuminating  agent.  It  dissolves  in  its  own 


DIPROPARGYL  53 

volume  of  water,  and  in  six  times  its  volume  of  alcohol;  is 
poisonous,  combining  with  the  hsemoglobin  of  the  blood, 
It  is  decomposed  into  its  elements  with  detonation  by  ex- 
plosive fulminate  of  silver,  and  also  by  the  electric  spark, 
It  combines  with  hydrogen  to  ethane,  when  heated  with  the 
latter  in  presence  of  platinum  black,  or  to  ethylene,  upon  treat 
ing  its  copper  compound  with  zinc  and  ammonia.  A  mixture 
of  acetylene  and  oxygen  explodes  violently  when  a  light  is 
applied  to  it.  Chromic  acid  oxidizes  acetylene  to  acetic  acid, 
and  permanganate  of  potash  to  oxalic  acid.  It  combines  with 
nitrogen  under  the  influence  of  the  induction  spark  to  hydro- 
cyanic acid  (see  this),  and  detonates  upon  being  mixed  with 
chlorine,  but  additive  products,  e.g.  C2H2C12,  can,  however,  be 
prepared.  As  little  as  ^J<y  milligramme  of  it  can  be  detected 
by  the  formation  of  the  dark-red  copper  compound  C2Cu2. 
This  latter  explodes  when  struck,  or  when  heated  to  a  little 
over  100°. 

Allylene  (Propine),  C3H4,  or  CH3»C:CH,  can  be  prepared 
from  propylene  bromide,  CH3  •  CHBr  •  CH2Br.  It  resembles 
acetylene. 

Allene  (Propadiene),  C3H4,  or  CH2:C:CH2,  is  obtained  by 
the  electrolysis  of  itaconic  acid.  It  is  gaseous,  and  does  not 
yield  metallic  compounds. 

Diallyl  (Hexa-l :  5 -diene),  CH2 : CH . CH2 . CH2 •  CH : CH2,  is 
obtained  from  allyl  iodide,  CH2:CH»CH2I,  and  sodium.  ^ 

Isomeric  with  these  hydrocarbons  are  certain  hydro-deriva- 
tives of  aromatic  hydrocarbons,  e.g.  tetrahydrobenzene,  C8H14; 
decahydronaphthalene,  C10H18.  (See  Aromatic  Compounds.) 


D.  Hydrocarbons  CnH, 


2n-« 


Di-acetylene  (Butadiine),  C4H2,  or  CH-C-C-CH.  This  is 
prepared  by  heating  the  ammonic  salt  of  diacetylene-dicar- 
boxylic  acid  (see  this)  with  ammoniacal  copper  solution, 
whereby  it  is  transformed  into  the  cuprous  compound  of  di- 
acetylene,  and  then  warming  this  with  potassium  cyanide.  It 
is  a  gas  of  a  peculiar  odour,  which  yields  a  violet-red  copper 
compound  and  a  yellow  silver  one,  the  latter  exploding  upon 


bromide,  and  the  subsequent  elimination  of  four  molecules  of 
hydric  bromide  from  each  molecule  of  the  tetra-bromide;  b.-pt. 


64  II.   HALOID   SUBSTITUTION  PRODUCTS 

85°.  It  gives  copper  and  silver  compounds,  and  takes  up  eight 
atoms  of  bromine,  &c.  It  possesses  an  especial  interest,  as  it 
is  isomeric  with  benzene.  Another  isomeride  is  2 : 4:-Hexadiine, 
CH3 .  C  i  C  •  C :  C  •  CH3.  (B.  20,  R.  564.) 


II.  HALOID  SUBSTITUTION  PRODUCTS  OF  THE 
HYDROCARBONS 

A.  Halogen  Derivatives  of  the  Paraffins 

These  are  to  be  regarded  as  paraffin  hydrocarbons  in  which 
one  or  more  hydrogen  atoms  have  become  replaced  by  one  or 
more  halogen  atoms. 

General  Properties. — Only  a  few  of  these  compounds,  e.g. 
CH3C1,  C2H5C1,  and  CH3Br,  are  gaseous  at  the  ordinary  tem- 
perature, most  of  them  being  liquid,  and  those  with  a  very 
large  number  of  carbon  atoms  in  the  molecule  solid,  e.g.  cetyl 
iodide,  C16H33I.  The  introduction  of  a  halogen  atom  in  any 
hydrocarbon  in  place  of  an  atom  of  hydrogen  always  tends  to 
raise  the  boiling-point;  the  introduction  of  iodine  has  the 
most  marked  effect,  and  chlorine  the  least  (cf.  Table,  p.  56). 
Such,  also,  as  contain  a  large  number  of  halogen  atoms,  e.g. 
CI4,  C2C16,  are  solid.  Under  comparable  conditions,  the  boiling- 
points  of  the  iodides  lie,  for  each  atom  of  halogen,  about  50° 
(40°-60°),  and  those  of  the  bromides  about  22°  (20°-24°), 
above  those  of  the  chlorides. 

The  lowest  members  of  the  series  have,  in  the  liquid  form, 
at  first  a  higher  specific  gravity  than  water,  e.g.  CH3I,  sp.  gr. 
2*2,  C2H5Br,  sp.  gr.  1'47.  With  an  increasing  number  of 
carbon  atoms,  however,  they  become  more  like  the  paraffins, 
the  influence  of  the  halogen  diminishes,  and  they  are  lighter 
than  water. 

The  halogen  substitution  products  of  the  hydrocarbons  are 
very  sparingly  soluble  in  water,  but  readily  in,  and  therefore 
miscible  to  any  extent  with,  alcohol  or  ether;  they  also  dissolve 
in  glacial  acetic  acid.  They  often  possess  a  sweet  ethereal 
odour,  but  this  becomes  less  marked  with  diminishing  vola- 
tility. Most  of  them  are  combustible;  thus  methyl  and  ethyl 
chloride  burn  with  a  green-bordered  flame,  while  ethyl  iodide 
and  chloroform  can  only  be  set  fire  to  with  difficulty.  Many 


MODES   OF  FORMATION  55 

members  of  the  series  containing  one  or  two  atoms  of  carbon 
produce  insensibility  and  unconsciousness  when  inhaled,  e.g. 
CHClg,  C2H3C13,  C2H5Br,  and  C2HC15.  The  liquid  iodine 
derivatives  are  readily  decomposed,  and  on  exposure  to  light 
turn  deep-brown  in  colour,  owing  to  the  liberation  of  free 
iodine,  e.g.  ethyl  iodide  liberates  iodine  and  gives  C4H10. 

In  all  these  compounds  the  halogen  is  more  firmly  bound 
than  in  inorganic  salts,  so  that,  for  instance,  when  silver 
nitrate  is  added  to  an  aqueous  solution  of  a  chlorine  com- 
pound, e.g.  chloroform,  it  causes  no  precipitation  of  AgCl. 
Nevertheless,  the  halogen  is  in  most  cases  readily  exchangeable 
for  other  elements  or  groups,  a  circumstance  of  the  utmost 
importance  for  many  organic  reactions.  This  is  especially 
true  for  the  iodine  and  .bromine  compounds,  which  react  more 
readily  than  the  chlorides,  and,  on  account  of  their  lesser 
volatility,  are  easier  to  work  with;  thus  C2ILBr  reacts  with 
AgN03  at  the  boiling  temperature,  and  C2H5I  in  the  cold 
even. 

In  all  these  halogen  compounds  the  halogen  can  be  again 
replaced  by  hydrogen  by  inverse  substitution,  e.g.  by  sodium 
amalgam,  by  zinc  dust  and  hydrochloric  or  acetic  acid,  or  by 
heating  with  hydriodic  acid.  (See  p.  33.) 

Of  fluorine  compounds,  only  a  few  are  known  as  yet;  CH3F 
and  C2H5F  are  gases. 

Nomenclature. — The  best  system  of  nomenclature  is  to  regard 
them  as  derived  from  the  corresponding  hydrocarbons,  e.g. 
CHClg  trichloro-methane,  CH3I  mono-iodo-methane,  and  if 
necessary  to  indicate  the  carbon  atoms  to  which  the  halogen 
radicals  are  attached,  e.g.  CH2C1«CH2C1  1 : 2-dichloro-ethane, 
CH3.CHBr2  l:l-dibromo-ethane,  CH2Br.CH2.CH2Br  l:3-di- 
bromo-propane,  CH3 .  CH(CH3) .  CHBr .  CH2  •  CH2Br  2-methyl- 
3 : 5-dibromo-pentane. 

The  following  are  some  of  the  most  important  methods  em- 
ployed for  the  preparation  of  these  halogen  derivatives : — - 

1.  By  Substitution. — Chlorination  and  Bromination.  Chlorine 
and  bromine  act  for  the  most  part  as  direct  substituents  (see 
p.  31)  With  the  gaseous  hydrocarbons  their  action  even  in 
the  cold  is  an  extremely  energetic  one  (e.g.  chlorine  mixed 
with  methane  easily  causes  an  explosion,  so  that  dilution  with 
C02  is  necessary);  the  higher  members  require  to  be  heated. 


56 


II.    HALOID  SUBSTITUTION   PRODUCTS 


HALOGEN  SUBSTITUTION  PKODUCTS 

Saturated  Compounds 

(a)  Mono-substituted  Derivatives. 


Chloride. 


B.-p. 
-237 

+  12-2° 
46-5° 
365° 

78° 


Sp.  gr. 
0-952 
0-918 
0-912 
0-882 
0-907 


Bromide. 


Iodide. 


Siy] 

Ethyl 

w-Propyl 

iso-Propyl 

Prim.  n-Butyl 

(b)  Di-substituted  Derivatives. 

Chloride. 
B.-p.     Sp.  gr. 

Methylene...  42°     1-337 

Ethylene 84°     T260 

Ethylidene...  58°*    M89 

(c)  Tri-substituted  Derivatives. 

Chloroform. 

CHX3 b.-p.  61° 


B.-p. 

+4-5° 

38-4° 

71° 

60° 

101° 


Sp.  gr. 

1-732 

1-468 
1-383 
1-340 
1-305 


B.-p. 
+45° 

72-3° 

102-5° 

89° 

130° 


Sp.gr 
2-293 
1-944 
1-786 
1-744 
1-643 


Bromide. 
B.-p.      Sp.  gr. 

97°  2-498 
131°  2-189 
110°  2-080 


Iodide. 

B.-p.      Sp.  gr. 
180°     3-292 
solid;  m.-p.  81-82r 
178°    2-84 


Bromoform.  lodoform. 

b.-p.  151°  melts  at  H9C 

sublimes 
(d}  Tetra-substituted  Derivative. 

Chloride.  Bromide. 

CX4 76°        solid;  m.-p.  92°;  b.-p.  189° 

Carbon  tetra- 


Unsaturated  Compounds 


Chloride. 

Vinyl,  CH2:CHX -18° 

Allyl,  CH2:CH.CH2X 46° 


Bromide.        Iodide. 
+23°  56° 

70°          101° 


Trichlorethylene  boils  at  88°,  tetrachlorethylene  at  121°. 
Monochlor-  and  monobrom-acetylene  are  gaseous. 

Compounds  of  the  type  CCl3Br,  CCl2Br2,  CC12I2,  &c.,  arc 
also  known. 


The  first  halogen  atom  enters  most  easily  into  the  com- 
pound, the  substitution  becoming  more  difficult  as  the  number 
of  those  atoms  present  increases.  In  the  case  of  the  higher 
hydrocarbons  there  usually  result  two  isomeric  mono-substi- 
tution products.  The  action  of  the  halogens  is  further  facili- 
tated by  sunlight,  and  by  the  presence  of  iodine,  this  latter 
acting  as  a  carrier  of  chlorine  by  the  alternate  formation  of 
IC13  and  IC1,  thus:  IC13  =  IC1  +  2  Cl.  Antimony  penta- 


FORMATION   OF  HALOGEN   DERIVATIVES  57 

chloride  and  ferric  chloride  act  in  the  same  way  (and  also  for 
brominating  and  iodating,— B.  18,  2017;  A.  231,  195);  iron 
wire  is  especially  useful  in  brominating  (B.  24,  4249).  When 
complete  chlorination  is  required,  the  substance  in  question  is 
repeatedly  saturated  with  chlorine  in  presence  of  iodine,  and 
heated  in  a  tube  to  a  high  temperature. 

From  methane  are  formed  the  whole  series  of  substitution 
products  up  to  CC14. 

Ethane  first  yields  ethyl  chloride,  C2H5C1,  then  ethylidene 
chloride,  C2H4C12,  and  so  on  up  to  C2C16. 

From  propane  is  first  produced  normal  propyl  chloride, 
03H7C1,  and  finally  C3C18.  The  latter  decomposes,  upon 
vigorous  chlorination,  first  into  C2C16  and  CC14,  and  the 
perchloro-ethane  subsequently  into  two  molecules  CC14.  On 
chlorinating  butane  and  the  higher  hydrocarbons  strongly,  an 
analogous  splitting  up  of  the  molecule  is  effected.  Strong 
chlorination  or  bromination  readily  gives  rise  at  the  same  time 
to  hexachloro-  or  hexabromo-benzene. 

Iodine  seldom  acts  as  a  direct  substituent,  since  by  this 
reaction  hydrogen  iodide  would  be  formed,  which  would  then 
reduce  the  iodine  compound  back  to  the  hydrocarbon.  (See 
p.  33.)  To  induce  the  action,  therefore,  the  HI  formed  must  be 
removed  by  HI03  or  HgO.  The  iodine  substitution  products  of 
the  hydrocarbons  are  usually  prepared  indirectly  (according  to 
2  or  3). 

2.  From  Unsaturated  Hydrocarbons.  These  combine  readily 
with  halogen  or  halogen  hydride.  (See  p.  44.) 

Ethylene  gives  with  hydrochloric,  hydrobromic,  and  hydri- 
odic  acids,  ethyl  chloride,  &c.,  i.e.  mono-substitution  products 
of  ethane;  with  chlorine,  &c.,  it  gives  di-substitution  products. 

The  compound  C2H4C12,  obtained  by  the  action  of  chlorine, 
is  called  ethylene  chloride,  has  the  constitutional  formula 
CH2C1.CH2C1,  and  is  isomeric  with  the  ethylidene  chloride 
CH3.CHC12,  obtained  by  the  chlorination  of  C2H5C1.  (For  an 
explanation  of  this  isomerism,  see  p.  62.) 

Propylene  combines  with  hydriodic  acid  to  isopropyl  iodide, 
C3H7I,  which  is  reconverted  into  propylene  by  elimination  of 
HI.  But  the  same  propylene  results  from  a  compound  isomeric 
with  isopropyl  iodide,  viz.  normal  propyl  iodide  (and  also,  of 
course,  from  the  above-mentioned  normal  propyl  chloride),  by 
the  elimination  of  hydrogen  iodide  (or  chloride),  so  that  by  this 
reaction  normal  propyl  iodide  can  be  transformed  into  iso- 
propyl iodide.  (See  p.  60.)  From  the  three  butylenes  there 


58  II.   HALOID  SUBSTITUTION  PRODUCTS 

are  formed  two  butyl  iodides,  viz.  secondary  and  tertiary, 
which,  as  well  as  the  two  other  existing  butyl  iodides,  yield 
these  butylenes  again  with  alcoholic  potash;  in  this  way  the 
two  last-mentioned  butyl  iodides  are  convertible  into  their 
isomers,  the  two  first  (see  p.  61). 

A  study  of  the  constitution  of  the  compounds  formed,  shows 
that  in  these  additive  reactions  the  halogen  invariably  attaches 
itself  to  that  carbon  atom  with  which  are  combined  the  least  number 
of  hydrogen  atoms,  e.g. 


CH3  •  CH :  CH2  -f  HI  =  CH3  •  CHI  •  CH3  (not  CH3  •  CH2  •  CH2I) ; 

from  C3H7X  onwards,  therefore,  we  obtain  only  "  secondary  " 
and  "  tertiary  "  *  compounds. 

3.  From  Compounds  containing  oxygen. 

(a)  From  the  alcohols  C^H^OH.  In  these  the  OH  is 
readily  exchangeable  for  chlorine,  bromine,  or  iodine  by  the 
action  of  halogen  hydride,  thus: — 

C2H6OH  +  HBr  ^±  C2H6Br  +  H20. 

In  such  exchange  the  halogen  takes  the  place  of  the  hy- 
droxyl,  so  that  the  constitution  of  the  haloid  product  corre- 
sponds with  that  of  the  alcohol  used. 

These  reactions  are  reversible  or  balanced,  and  a  state  of 
equilibrium  is  reached;  according  to  the  law  of  mass  action, 
it  is  therefore  necessary  either  to  use  a  large  excess  of  halogen 
hydride  (e.g.  to  saturate  with  the  gas  or  to  heat  in  a  sealed 
tube),  or  to  remove  the  water  formed,  by  sulphuric  acid,  zinc 
chloride,  &c. 

Methyl  and  ethyl  chlorides  are  easily  prepared  by  distilling 
the  corresponding  alcohol  with  common  salt  and  sulphuric 
acid,  or  by  leading  hydrochloric -acid  gas  into  the  warmed 
alcohol  containing  half  its  weight  of  zinc  chloride  in  solution 
(Groves). 

The  chlorides  of  phosphorus  are  also  applicable  for  the  sub- 
stitution of  OH  by  Cl,  since  they  react  in  the  same  way  with 
alcohols  as  with  water,  thus : 

POL  +  3  HOH       =  P(OH)3  4-  3  HC1 
PC13  4-  3C2H6OH  =  P(OH)3  4-  3C2H6C1. 

*  The  names  "primary",  "secondary",  and  "tertiary"  compounds  are 
founded  upon  those  of  the  alcohols— primary,  secondary,  and  tertiary— ir 
question,  from  which  they  can  be  prepared  according  to  method  3,  a. 


MONO-SUBSTITUTION  PRODUCTS  59 

Phosphorus  pentachloride  is  most  frequently  used  for  this 
purpose, 

PC16  H-  C2H6OH  =  C2H6C1  +  HC1  +  POC13. 

Phosphorus  oxychloride  itself  is  also  sometimes  employed. 
Of  especial  importance  here  is  the  application  of  the  halogen 
compounds  of  phosphorus  in  the  production  of  bromine  and 
iodine  compounds.  The  former  need  not  be  prepared  before 
band,  the  end  being  achieved  by  gradually  bringing  phosphorus 
and  iodine  or  bromine  together  in  presence  of  the  alcohol: 
3CH3OH  +  P  +  31  =  3CH3I 


This  is  the  method  usually  employed  for  the  preparation  of 
methyl  and  ethyl  iodides. 

(b)  The   halogen  -derivatives   may   also  be  prepared  from 
polyhydric   alcohols,  e.g.   trichlorhydrin,   C3H6C13,   from  gly- 
serol,  C3H5(OH)3,  and  PC15;  isopropyl  iodide,  C3H7I,  or  allyl 
iodide,  C3H5I,  from  glycerol  and  PI3  according  to  the  con- 
ditions of  the  experiment  (see  p.  60);  hexyl  iodide,  C6H13I, 
from  mannitol,  C6H8(OH)6  and  HI,  the  latter  acting  here  as 

t  reducing  agent  also. 

(c)  From  aldehydes  and  ketones  (see  these),  dichloro-sub- 
stitution  products  are  formed  by  the  action  of  PC15,  e.g.  ethyli- 
lene  chloride,  CH3.CHC12,  from  aldehyde,  CH3.CH:0;  ace- 
tone chloride,  CH3  •  CC12  •  CH3,  from  acetone  CH3-CO-CH3. 

4.  Chlorine  and  bromine  compounds  are  frequently  formed 
Tom  the  corresponding  iodine  or  bromine  ones  by  direct  ex- 
change, e.g.  isopropyl  bromide  from  the  iodide,  or  methylene 
>romide  from  methylene  iodide ;  (also  by  treatment  with  mer- 
curic chloride,  stannic  chloride,  or  fuming  hydrochloric  acid). 
Conversely  the  chlorides  and  bromides  may  be  transformed 
nto  the  iodides  by  heating  with  sodium  iodide  in  alcoholic 
jr  acetone  solution  (B.  18,  519),  dry  calcium  iodide  (B.  16, 
392),  or  with  fuming  hydriodic  acid. 

MONO-SUBSTITUTION  PKODUCTS 

The  methyl  and  ethyl  compounds  are  usually  obtained  from 
fche  corresponding  alcohols  by  one  or  other  of  the  following 
methods:— (a)  Grove's  method  (p.  58);  (b)  action  of  concen- 
trated sulphuric  acid  and  sodium  halide;  (c)  phosphorus  and 
halogen. 

Methyl  chloride  is  often  obtained  by  heating  trimethy- 
lamine  hydrochloride  at  360°.  (For  physical  properties,  see 


60  II.    HALOID   SUBSTITUTION   PRODUCTS 

Table.)  Methyl  chloride  is  used  for  the  production  of  artificiE 
cold,  for  extracting  perfumes  from  flowers,  and  for  methylal 
ing  dyes  in  the  colour  industry.  It  burns  with  a  greer 
bordered  flame. 

Ethyl  Fluoride,  C2H5F.  A  gas  of  ethereal  odour,  whic 
liquefies  at  —48°;  it  burns  with  a  blue  flame,  and  does  no 
attack  glass. 

Each  Propyl  halide,  C3H7X,  exists  in  two  isomeric  form* 
the  normal  propyl  and  the  isopropyl  compounds,  the  forme 
boiling  at  a  somewhat  higher  temperature  than  the  latter.  T 
the  normal  compounds  the  constitutional  formula  CH3'CH2 
CH2X  is  ascribed,  and  to  the  iso-compounds  the  formul 
CH3»CHX'CH3,  since  they  are  derivable  respectively  fror 
normal  propyl  alcohol  and  from  isopropyl  alcohol  or  acetone 
the  constitutions  of  which  can  readily  be  determined. 

According  to  theory  only  these  two  cases  are  possible,  sine 
propane,  CH3«CH2'CH3,  contains  but  two  types  of  hydroge 
atoms,  viz.:  (1)  six  combined  with  the  end  carbon  atoms,  an< 
(2)  two  combined  with  the  middle  ones.  For  the  transform* 
tion  of  the  normal  into  the  iso-compounds,  see  p.  57. 

Isopropyl  iodide,  2-iodopropane,  is  prepared  from  glycero 
phosphorus,  iodine,  and  water  (see  p.  59);  allyl  iodide  (p.  65 
is  formed  as  intermediate  product,  and  at  the  same  time  som 
propylene  (p.  48): 

C3H6(OH)3  +  SHI  -  3H20  =  C3H6I3  =  C3H6I  +  I2. 
C3H6I  +  HI  =  C3H6  +  I2.         C3H6I  -f  2  HI  =  C3H7I  +  I2. 

Each  Butyl-haloid  compound,  C4H9X,  is  known  in  for 
isomeric  forms,  which  differ  from  one  another  in  boiling-poir 
(up  to  30°). 

Four  isomers  are  theoretically  possible;  thus  from  norm? 
butane,  CH3-CH2.CH2.CH3,  are  derived: 

(a)  CH3.CH2.CH2.CH2I        and       (b)  CH3.CH2.CHI.CH3 

Normal  butyl  iodide  (I-iodobutane)  Secondary  butyl  iodide  (2-iodobutane 

according  to  whether  a  "  terminal "  or  "  central "  hydroge 
atom  is  replaced;  similarly  from  trimethylmethane,  CH(CH3) 
are  derived: 

(c)  ™3>CH.CH2I        and        (d)  £]|j>CI.CH3 

Is'obutyl  iodide  Tertiary  butyl  iodide 

(Z-methyl-B-iodopropane)  (Z-methyl-Z-iodopropane). 

The   constitutions  of   these   four  compounds   follow   fror 


Y 


DI-SUBSTITUTION   PRODUCTS  61 

hose  of  the  four  corresponding  butyl  alcohols  (p.  67),  from 
hich  they  can  be  prepared  by  the  action  of  halogen  hydride. 
For  transformations,  see  p.  58.  Isobutyl  bromide  changes 
nto  the  tertiary  compound  when  heated  at  230°-240°,  prob- 
bly  owing  to  the  intermediate  formation  of  butylene. 

The  Isobutyl  compounds  are  the  easiest  to  prepare  (from 
sobutyl  alcohol).  The  Tertiary  readily  react  with  H20  to 
orm  the  alcohol  and  halogen  hydride,  this  taking  place  even 
n  the  cold  in  the  case  of  the  iodide. 

These  mono-halogen  derivatives  are  one  of  the  most  impor- 
ant  groups  of  reagents  employed  by  the  organic  chemist,  on 
ccount  of  the  readiness  with  which  the  halogen  atoms  may 
>e  replaced  by  other  radicals. 

ome  of  the  more  characteristic  reactions  are: — 
I.  Eeplacement  of  halogen  by  hydrogen.     Inverse  substi- 
,1C  ution  (see  p.  33). 
,e     2.  Eeplacsment  of  halogen  by  OH  (hydroxyl)  (p.  71), 

C2H5I  +  H20  =  C2H6OH  +  HI, 

generally  by  the  aid  of  aqueous  alkali,  moist  silver  oxide,  or 
ead  oxide  and  water. 

3.  Alkalis   in  alcoholic  solution,  or  alcoholic  solutions  of 
odium  methoxide  (CH3  •  ONa)  or  sodium  ethoxide  (C2H5  •  ONa), 
is  a  rule,   eliminate   halogen   hydracids,  and  yield  olefines, 
3H2I«CH3  —  HI  =  CH2:CH2.     For  the  reaction  it  is  neces- 
ary  that  the  halogen  derivative  contain  at  least  two  carbon 
atoms,  and  that  a  hydrogen  atom  should  be  attached  to  a  car- 
)on  atom  adjacent  to  the  one  to  which  the  halogen  is  united. 

4.  The  halogen  may  be  replaced  by  the  amino  group  .NH2 
by  the  aid  of  ammonia  under  pressure,  by  the  nitro  group 

or  nitrite  radical  .0«N:0  (p.  94),  and  by  the  nitrile 


radical  .C|N  (p.  100). 
For  their  use  as  synthetical  reagents,  see  pp.  121,  228,  237. 

DI-SUBSTITUTION  PRODUCTS 

Methylene  chloride,  CH2C12,  Methylene  bromide,  CH2Br2, 
ind  Methylene  iodide,  CH2I2,  are  colourless  liquids  which 
ire  obtained  either  from  the  tri-haloid  substitution  products 
Dy  inverse  substitution,  or  from  the  mono-substitution  pro- 
lucts  by  the  introduction  of  more  halogen.  (See  table, 

56.) 


62  II.    HALOID  SUBSTITUTION   PRODUCTS 

The  compounds  C2H4X2  are  known  in  two  isomeric  forms, 
to  which  are  assigned  the  constitutional  formulae: 

CH2X-CH2X  (ethylene)    and    CH3-CHX2  (ethylidene). 

The  former  result  from  the  addition  of  halogen  to  ethylene,  or 
from  the  action  of  halogen  hydride  or  phosphorus  haloids  upon 
glycol,  C2H4(OH)2  (see  this),  e.g.  ethylene  bromide,  by  passing 
ethylene  into  bromine  and  water  at  the  ordinary  temperature. 

The  ethylene  compounds  yield  acetylene  with  alcoholic 
potash,  or  better,  alcoholic  solution  of  sodium  ethoxide,  and 
are  transformed  into  glycol  by  exchanging  their  halogen  atoms 
for  hydroxyl  under  the  influence  of  potassium  carbonate  solu- 
tion. Glycol,  CH2(OH).CH2.OH,  with  hydrochloric  acid 
yields  glycol  mono-chlorhydrin,  CH2C1  •  CH2  •  OH,  and  this  on 
oxidation  yields  mono-chloracetic  acid,  CH2C1-CO»OH.  In 
this  acid  it  can  be  shown  that  the  chlorine  and  hydroxyl 
radicals  are  attached  to  distinct  carbon  atoms;  hence  in 
glycol  the  two  hydroxyl  groups,  and  in  ethylene  dibromide 
the  two  bromine  atoms,  are  almost  certainly  united  to  distinct 
and  not  to  the  same  carbon  atoms. 

The  Ethylidene  compounds  are  obtained  from  aldehyde 
(para-aldehyde)  by  exchange  of  the  oxygen  for  halogen  by 
means  of  phosphorus  chloride,  &c. 

Ethylidene  chloride,  also  called  ethidene  chloride,  or  1:1- 
dichloroethane,  is,  however,  most  conveniently  prepared  with 
phosgene,  COC12,  thus: — 

CH3.C<J  +  COC12  =  C 

It  is  also  formed  by  the  further  chlorination  of  CgHgCl,  and  is 
a  by-product  in  the  manufacture  of  chloral.  Its  boiling-point 
(57°)  is  lower  than  that  of  ethylene  chloride  (84°).  It  is  an 
anaesthetic. 

Propylene  chlorides,  C3H6C12,  bromides  and  iodides,  are 
likewise  known.  One  group  is  formed  by  the  addition  of 
halogen  to  propylene,  and  thus  has  an  unsymmetrical  con- 
stitution, e.g.  propylene  chloride,  1:2-  dichloropropane, 
CH3»CHC1  •CHgCl.  Isomeric  .with  this  group  are  the  sym- 
metrically-constituted Trimethylene  derivatives,  of  which  tri- 
methylene-bromide,  1 : 3-dibrorno-propane,  CH2Br  •  CH2  •  CH2Br, 
results  from  the  addition  of  hydrobromic  acid^to  allyl  bromide ; 

=  CH2Br.CH2.CH2Br. 


CHLOROFORM,   ETC.  63 

TRI-SUBSTITUTION  PRODUCTS 

Chloroform,  CHC13  (Liebig  and  Soubeiran,  1831;  formula 
established  by  Dumas,  1835). 

Fwmation.  —  1.  From  methane  and  methyl  chloride  (see 
p.  57).  2.  By  heating  alcohol,  or  even  better,  acetone,  with 
bleaching  -powder  and  water.  When  alcohol  is  used,  the 
bleaching-powder  probably  first  oxidizes  it  to  aldehyde,  then 
chlorinates  to  chloral,  and  ultimately  hydrolyses  (see  below) 
to  chloroform.  3.  Together  with  alkali  formate  by  warming 
chloral  or  chloral  hydrate  with  aqueous  alkali: 


CCl3.CHO  +  NaOH  =  CHC13  +  HC02Na. 

This  last  method  of  formation  is  the  best  for  the  preparation 
of  pure  chloroform. 

It  is  a  colourless  liquid  of  a  peculiar  ethereal  odour  and 
sweetish  taste,  is  sparingly  soluble  in  water,  and  solidifies 
below  -70°.  B.-pt.  61-2°.  Sp.  gr.  1-527.  It  dissolves  fats, 
resins,  caoutchouc,  iodine,  &c.,  and  is  also  a  most  valuable 
anaesthetic  (Simpson,  Edinburgh,  1848). 

The  carbylamine  reaction  (see  Iso-nitriles)  furnishes  a  deli- 
cate test  for  the  presence  of  chloroform. 

Bromoform,  CHBr3,  is  sometimes  present  in  commercial 
bromine. 

lodoform,   CHI3   (Serullas,    1822;    formula   established  by 
Dumas),  is   prepared  by  warming   alcohol    with   iodine  and 
ulkali  or  alkaline  carbonate: 
C2H5OH  +  4  12  +  6  KOH  =  CHI3  +  HCO2K  +  5  KI  +  5  H2O. 

It  can  also  be  prepared  in  the  same  way  from  acetone, 
aldehyde,  lactic  acid,  and,  generally,  from  compounds  which 
"contain  the  group  CH3  •  CH(OH)  -  C,  or  GHg-GQ-G  (Ueben). 

An  electrolytic  method  consists  in  passing  an  electric  current 
through  a  solution  containing  potassium  iodide,  sodium  car- 
bonate, and  alcohol,  the  temperature  being  kept  at  65°.  Some 
85  per  cent  of  the  potassium  iodide  is  thus  converted  into 
iodoform. 

It  crystallizes  in  yellow  hexagonal  plates,  melts  at  119°,  has 
a  peculiar  odour,  is  volatile  with  steam,  and  is  an^  important 
antiseptic.  It  contains  only  0'25  per  cent  H,  which  at  first 
caused  the  presence  of  the  latter  to  be  overlooked. 

Methyl  chloroform,  CH3-CC13.  This  compound,  the  tri- 
chloride of  acetic  acid,  also  acts  as  an  anaesthetic. 


64  II.   HALOID   SUBSTITUTION   PRODUCTS 

Glyceryl  chloride,  Trichlorhydrin,  l:2:3-trichloropropane, 
CHgCl-CHCl-CHjCl,  is  obtained  from  glycerol  and  PC15 
(p.  59).  B.-pt.  158°.  The  corresponding  bromine  compound 
is  also  known,  but  not  the  iodine  one,  C3H5I3,  which  decom- 
poses in  the  nascent  state  (i.e.  when  glycerine,  phosphorus, 
and  iodine  react  together)  into  allyl  iodide,  C3H5I,  and  I2. 

HIGHER  SUBSTITUTION  PRODUCTS 

Carbon  tetrachloride,  CC14.  Can  be  prepared  from  chloro- 
form or  carbon  disulphide  and  chlorine.  It  is  a  colourless 
liquid,  boils  at  77°,  and  is  used  as  a  solvent  for  fats,  &c. 

Perchloro-ethane,  C2CI6.  Ehombic  plates  of  camphor-like 
odour.  Melts  and  sublimes  at  185°. 

The  chemical  properties  of  these  polyhalogen  derivatives 
are  somewhat  similar  to  those  of  the  monohalogen  derivatives. 
They  may  be  reduced,  transformed  into  the  corresponding 
alcohols,  or  the  halogen  atoms  replaced  by  NH2  radicals,  &c. 
The  action  of  alkalis  on  the  polyhalogen  derivatives,  in  which 
the  halogen  atoms  are  attached  to  the  same  carbon  atom, 

OTT 

is  interesting,  e.g.  CH2C12  gives  not  CH2<^QTT,  but  CH2:0 

formaldehyde  and  H20;  CHC13  gives  not  CH(OH)3,  but  this 
compound  —water,  viz.  0:CH«OH,  formic  acid.  Similarly, 
C014  gives  not  C(OH)4,  but  C02  +  2H20,  and  CH3.CHBr2 
gives  CH3.CH(OH)2  -  H20,  i.e.  CH3.CHO. 

Many  of  these  reactions  require  high  temperatures;  the 
substances  must  be  heated  with  the  alkali  in  sealed  tubes 
under  pressure.  It  is  characteristic  of  carbon  derivatives 
that  compounds  which  contain  two  or  more  hydroxyl  radicals 
attached  to  the  same  carbon  atom  are  unstable,  and,  as  a  rule, 
immediately  eliminate  water  yielding  an  aldehyde,  acid,  &c. 
Ammonia  and  chloroform  at  a  red  heat  yield  HCN  and  HC1. 

B.  Haloid  Derivatives  of  the  Unsaturated 
Hydrocarbons 

These  compounds  are  obtained  either  by  partially  withdraw- 
ing halogen  or  halogen  hydride  from  the  halogen  derivatives 
of  the  saturated  hydrocarbons,  or  by  incompletely  saturating 
the  hydrocarbons  poorer  in  hydrogen  with  halogen  or  halogen 
hydride,  e.g. : 

C2H4Br2  -  HBr  =  C2H3Br.    C2H2  -f  HBr  =  C?H3Br. 


III.   MONOHYDRIC  ALCOHOLS  65 

The  allyl  compounds,  C3H5X,  are  obtained  from  ailyl  alcohol 
and  halogen  hydride  or  phosphorus  haloids. 

These  unsaturated  products  are  very  similar  to  the  corre- 
sponding saturated  ones,  but  they  are,  of  course,  capable  of 
combining  further  with  halogen  or  halogen  hydride,  and  they 
exist  in  stereo-isomeric  modifications.  (See  Fumaric  Acid.) 

In  the  unsaturated  compounds  the  halogen  atoms  are,  as  a 
rule,  not  so  readily  replaced  by  other  radicals,  e.g.  OH,  NH2, 
as  in  the  saturated  halogen  derivatives. 

The  following  may  be  mentioned : — 

Vinyl  bromide,  bromo-ethylene,  CH2:CHBr;  is  usually  pre- 
pared from  ethylene  di-bromide  and  alkali. 

Allyl -chloride,  -bromide,  and  -iodide,  3-iodo-l-propene, 
CH2:CH.CH2X. 

These  are  of  importance  on  account  of  their  relation  to  the 
allyl  compounds  found  in  nature,  e.g.  oil  of  mustard  and  oil  of 
garlic.  The  iodide  is  prepared  from  glycerol,  phosphorus,  and 
iodine,  and  from  it,  by  means  of  HgCl2,  the  chloride. 

Isomeric  with  these  are  the  propylene  compounds,  e.g. 
a-chloro-propylene  (I-chloro-l-propene),  CHC1:CH«CH3. 


III.  MONOHYDRIC  ALCOHOLS,   OR  ALKYL 
HYDROXIDES 

Alcohols  may  be  regarded  as  paraffins  in  the  molecules  of 
which  one  or  more  hydrogen  atoms  have  been  replaced  by  one 
or  more  monovalent  hydroxyl  groups,  •  0  •  H.  The  •  0  •  H  group 
is  thus  characteristic  of  alcohols.  For  the  proof  of  the  presence 
of  the  OH  group,  see  p.  17.  They  are  usually  divided  into 
groups,  according  to  the  number  of  such  radicals  contained  in 
the  molecule:  d%dnc,e.g.C2H4(OH)2;  trihydric, e.g. C3H5(OH)3 ; 
hemhydric,  e.g.  C6H8(OH)0,  &c. 

The  monohydric  alcohols  are  either  saturated  or  unsaturated, 
according  to  the  hydrocarbons  from  which  they  are  derived. 
The  unsaturated  closely  resemble  the  saturated,  except  that 
they  are  capable  of  forming  additive  compounds. 


(B480) 


66  III.    MONOHYDRIC  ALCOHOLS 

A.  Monohydrie  Saturated  Alcohols,  CnHto+1OH 

(See  Table,  p.  67.) 

The  lowest  members  of  this  series  are  colourless  mobile 
liquids,  the  middle  ones  are  more  oily,  and  the  highest — from 
dodecyl  alcohol,  C12H25OH,  onwards — are  solid  at  the  ordi- 
nary temperature,  and  like  paraffin  in  appearance.  Gaseous 
alcohols  are  unknown;  and  it  is  thus  obvious  that  the  intro- 
duction of  OH  for  H  raises  the  boiling-point  of  a  substance. 
Compare — 

B.-p.  B.-p. 

CH4 -164°     CH3OH 66° 

C«H, -93°     C9H5OH 78° 

C!2H6(OH) 78°     C;H4(OH)2 197° 

With  compounds  of  analogous  constitution  the  boiling- 
point  rises  with  tolerable  regularity;  in  the  case  of  the  lower 
members  by  about  19°,  and  higher  up  in  the  series  by  a 
smaller  number. 

The  lowest  members  are  miscible  with  water,  but  this 
solubility  rapidly  diminishes  as  the  molecular  weight  in- 
creases; thus  butyl  alcohol  requires  12  parts,  and  amyl  alco- 
hol 40  parts  of  water  for  solution,  while  the  higher  members 
are  no  longer  soluble  in  water.  The  former  can  be  separated 
or  "salted  out"  from  their  aqueous  solution  by  the  addition 
of  salts,  e.g.  K2C03  and  Ca012. 

The  specific  gravity  is  always  <  1.  The  highest  members 
(over  C16)  can  be  distilled  undecomposed  only  in  a  vacuum; 
at  the  ordinary  pressure  they  break  up  into  olefine  and  water. 
The  lowest  members  possess  a  spirituous  odour,  those  with 
more  than  five  C  atoms  an  odour  of  fusel,  and  both  have  a 
burning  taste,  while  the  highest  members  are  like  paraffin  in 
appearance  and  without  either  taste  or  smell. 

CONSTITUTION   AND  ISOMERS;    CLASSIFICATION  OF  THE 
ALCOHOLS 

Propyl  alcohol,  C3H7  •  OH,  and  the  higher  members  exist  in 
different  isomeric  modifications;  thus  there  are  two  propyl, 
four  butyl,  and  eight  amyl  alcohols,  &c. 

The  number  of  isomeric  forms  theoretically  possible  can  be 
determined  by  taking  the  formulae  for  the  corresponding  satu- 
rated hydrocarbons,  and  seeing  in  how  many  different  positions 


MONOHYDRIC   SATURATED   ALCOHOLS 


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68  III.    MONOHYDRIC  ALCOHOLS 

the  OH  group  can  be  introduced,  e.g.  CH3  •  CH2  •  CH3,  propane, 
can  obviously  give — 

CH3.CH2.CH2.OH    and    CH3.CH(OH).CH,, 

two  distinct  propyl  alcohols. 
Butane  exists  in  two  forms : 

CH3  •  CH2  •  CH2  •  CH3  or  normal    and    (CH3)3CH  or  iso. 

From  the  n  we  can  get — 

CH3.CH2.CH2.CH2.OH    and    CH3.CH2.CH(OH)-CH3; 

from  the  iso — 

(CH3)2CH  •  CH2  •  OH    and    (CH3)3C  •  OH; 

but  no  more. 

Of  these  isomerides,  some  only  are  oxidizable  to  acids, 
CnH2nO2,  containing  an  equal  number  of  carbon  atoms,  an 
aldehyde,  CnH2nO,  being  formed  as  intermediate  product. 
Such  alcohols  are  termed  primary  alcohols  (primary  propyl, 
butyl,  and  isobutyl  alcohols,  &c.). 

Another  class  of  alcohols  is  not  oxidizable  to  acids  with 
an  equal  number  of  atoms  of  carbon,  but  to  ketones,  CnH2nO, 
by  the  removal  of  2  atoms  of  hydrogen,  e.g.  isopropyl  alcohol 
yields  acetone,  C3H60.  These  are  termed  secondary  (secon- 
dary butyl  alcohol).  Upon  further  oxidation  the  ketones  do 
indeed  yield  acids,  which,  however,  contain  not  an  equal  but 
always  a  smaller  number  of  carbon  atoms,  the  carbon  chain 
having  thus  been  broken  up. 

Lastly,  the  third  class  of  alcohols,  the  tertiary,  yield  upon 
oxidation  neither  aldehydes,  ketones,  nor  acids  with  an  equal 
number  of  carbon  atoms,  but  only  ketones  or  acids  containing 
fewer  atoms  of  carbon. 

Constitution  of  the  Alcohols. — In  the  molecule  of  a  mono- 
hydric  alcohol  one  of  the  hydrogen  atoms  plays  a  part  different 
from  that  of  the  others;  thus  it  is  replaceable  by  metals  (K 
and  Na),  and  by  acid  radicals,  and,  together  with  the  oxygen 
atom,  combines  with  the  hydrogen  of  a  halogen  hydride  to 
form  water,  while  the  other  hydrogen  atoms  of  the  alcohol 
remain  unchanged.  This  hydrogen  atom,  which  has  already 
been  formulated  under  the  Theory  of  Types  apart  from  the 
others,  is  called  the  "typical"  or  "extra-radical"  hydrogen 
atom.  It  is  not  joined  directly  to  the  carbon  atom,  but 
through  the  oxygen  one,  a  conclusion  which  is  confirmed  by 


CONSTITUTION   OF  MONOHYDRIO  ALCOHOLS  69 

the  formation  of  alcohols  by  the  action  of  alkalis  (KOH)  on 
monohalogen  derivatives  of  the  paraffins.  (See  p.  71.)  This 
point  has  been  previously  discussed  (p.  17)  for  ethyl  alcohol. 

The  alcohols  therefore  contain  a  hydroxyl  group,  OH,  and 
their  general  constitutional  formula  is  (CnH2n+1)  •  OH. 

According  to  theory,  this  hydroxyl  can  either  replace  an 
atom  of  hydrogen  in  a  methyl  group,  in  which  case  an  alcohol 
containing  the  group  »CH2OH  (one  carbon  atom  being  joined 
to  the  other  by  a  single  bond)  results,  e.g.  CHg'CHg'OH. 
Or  it  can  replace  the  hydrogen  of  a  CH2  :  group  in  a  hydro- 
carbon, so  that  the  resulting  compound  contains  the  group 
:CH'OH,  the  carbon  being  here  joined  to  two  other  carbon 
atoms.  Or,  lastly,  it  is  possible  that  in  a  hydrocarbon  with 
a  branching  carbon  chain,  the  hydrogen  of  a  methine  group 
CH*  may  be  replaced  by  hydroxyl,  when  the  resulting  alcohol 
would  contain  the  group  :C»OH,  in  which  one  carbon  atom  is 
joined  to  three  others. 

TT 

Now,  it  is  easy  to  see  that  the  group  mG^\r\2ii  can)  by 


further  oxidation,  be  transformed  into  *G\Q.jj-     The  latter, 

which  is  termed  carboxyl,  is  contained  in  the  acids  CJI^O^ 
or  Cn.jHgn^COOH,  which  are  formed  by  the  oxidation  of  the 
primary  alcohols.  Consequently  it  is  the  primary  alcohols 
which  contain  the  group  •CH2«OH. 

The  group  :CH-OH  can  likewise  be  changed  into  :C:0 

(i.e.    C<Cojj  —  H20\  which  is  the  characteristic  group  of 

the  ketones,  by  oxidation.  A  further  introduction  of  0  or 
OH,  whereby  acids  containing  the  group  »CO'OH  would 
ensue,  is  not  possible  in  this  case  without  a  rupture  of  the 
carbon  chain,  since  the  carbon  atom  is  tetravalent.  Since 
then  it  is  the  secondary  alcohols  which  upon  oxidation  yield 
ketones,  and  not  acids  with  an  equal  number  of  carbon  atoms, 
the  group  :CH-OH  is  characteristic  of  these. 

Finally,  the  group  jC-OH  already  contains  the  maximum 
of  oxygen  which  can  be  combined  with  a  carbon  atom  already 
linked  to  3  other  atoms  of  carbon.  A  compound,  therefore,  in 
which  this  atomic  group  is  present,  cannot  yield,  when  oxi- 
dized, an  aldehyde,  acid,  or  ketone  with  an  equal  number  of 
carbon  atoms  in  the  molecule,  but  the  result  of  such  oxidation 
must  be  the  breaking  of  the  carbon  chain,  and  the  formation 
of  acids  or  ketones  containing  a  smaller  number  of  carbon 


70  III.   MONOHYDRIC  ALCOHOLS 

atoms  in  the  molecule.  This  being  the  behaviour  of  tertiary 
alcohols,  the  group  iC-OH  is  peculiar  to  them. 

The  existence  of  the  three  classes  of  alcohols  finds  in  this 
\vay  a  thoroughly  satisfactory  explanation  from  theory. 

The  secondary  and  tertiary  alcohols  were  predicted  by  Kolbe 
in  1859  from  theoretical  considerations  (A.  113.  301:  132, 
102). 

Among  the  isomeric  alcohols  the  primary  possess  the  highest, 
and  the  tertiary  the  lowest  boiling-points  (cf.  p.  67).  Similar 
generalizations  appear  to  hold  good  for  other  physical  pro- 
perties, e.g.  specific  gravity,  specific  refractive  indices,  and 
capillarity  constants.  The  tertiary  have  the  highest  melting- 
points. 

Determination  of  Constitution.  —  The  determination  of  the  con- 
stitution of  any  special  alcohol  is  based  largely  on  its  method 
of  formation  and  on  its  products  of  oxidation.  E.g.  Isopropyl 
alcohol  may  be  obtained  by  the  reduction  of  acetone  (CH3)2 
C:O,  and  must  therefore  have  the  constitutional  formula 
(CH3)2.CH.OH,  and  not  CH3.CH2-CH2.OH.  This  is  con- 
firmed by  the  fact  that  on  oxidation  it  yields  the  ketone 
acetone,  and  must  necessarily  be  a  secondary  alcohol  with 
the  grouping  :CH-OH. 

Similarly  isobutyl  alcohol  must  be  represented  as  (CH3)2- 
CH«CH2'OH,  since  on  oxidation  it  yields  zso-butyric  acid, 
the  constitution  of  which  is  known  to  be  (CH^-CH-CO-OH. 

Occurrence.  —  Different  alcohols  are  found  in  nature  combined 
with  organic  acids  as  esters  in  ethereal  oils  and  waxes;  e.g. 
methyl,  ethyl,  butyl,  hexyl,  and  octyl  alcohols,  and  also  those 
with  16,  27,  and  30  carbon  atoms;  ethyl  alcohol  also  occurs  in 
the  free  state. 

/.  General  Methods  of  Formation.  —  1.  By  "  saponification  "  or 
"hydrolysis"  of  their  esters,  i.e.  by  boiling  these.  with  alkalis  or 
mineral  acids,  or  by  the  action  of  superheated  steam,  thus:  — 

C6H5.CO-OC2H6-f  KOH  =  CCH5.(X).OK  +  C2H6OH. 
Ethyl  benzoate  Potassium  benzoate. 

Some  esters,  e.g.  ethyl  hydrogen  sulphate,  decompose  when 
simply  warmed  with  water: 

/SO2VOH"+H-OH  =  C2Hf).OH  +  SO2(OH)2. 


Most  of  these  processes  of  hydrolysing  require  some  little 
time,  and  the  ester  is  boiled  with  the  alkali  (KOH  solution) 
in  a  flask  fitted  with  a  reflux  condenser. 


METHODS   OF  FORMATION  71 

2.  From  the  halogen  compounds  CnH2n+1X,  and  therefore 
indirectly  from  the  paraffins  and  olefines  (pp.  55  and  57).  In 
the  latter  case  secondary  or  tertiary  alcohols,  from  C3  on,  are 
obtained  since  the  halogen  of  the  haloid  compounds  becomes 
attached  to  that  carbon  atom  to  which  the  smaller  number  of 
hydrogen  atoms  are  united. 

(a)  By  warming  these,  especially  the  iodides,  with  excess  of 
water  to  100°;  sometimes  by  simply  allowing  the  mixture  to 
stand  (tertiary  iodides)  : 

C2H6};+HX)H  =  C2H5.OH-f  HI. 

When  but  little  water  is  used,  a  state  of  equilibrium  is 
reached  as  the  reaction  is  reversible.  These  halogen  com- 
pounds may  also  be  termed  the  esters  of  the  halogen  hydracids, 
so  that,  strictly  speaking,  the  mode  of  formation  2  a  is  in- 
cluded in  1. 

(b)  Frequently  by  digesting  with  moist  silver  oxide  (which 
acts  here  like  the  unknown  hydroxide,  AgOH),  or  by  boiling 
with  lead  oxide  and  water: 

OH  =  C2H6.OH 


(c)  Upon  warming  with  silver  or  potassium  acetate,  the 
acetate  of  the  alcohol  in  question  is  formed,  and  this  is  then 
hydrolysed  : 

C2H5I  +  CH,  •  COO  Ag     =  CH3  -  COOC2H6  +  Agl 
CH3.COOC2H5  +  HOK  =  C2H6-OH  +  CH^COOK. 

3.  By  the  fermentation  of  the  carbohydrates  (e.g.  grape-sugar), 
the  alcohols  with  2,  3,  4,  5,  and,  under  certain  conditions,  even 
6  atoms  of  carbon  are  produced.     (Yeast  fermentation.) 

4.  On  treating  the  primary  amines  (see  these)  with  nitrous 
acid: 


5.  From  polyhydric  alcohols  by  replacing  several  of  the 
hydroxyl  groups  by  halogen  atoms,  and  then  reducing  the 
halogen  derivative: 

C3H6(OH)3  +  2HC1  =  C3H6C12(OH)  +  2H2O. 

Glycerol  Dichlor-hydrin. 

C3H6(OH)C12  +  4H  =  C3Hr.OH  +  2HC1. 
Isopropyl  alcohol. 

Secondary  alkyl  iodides  are  often  obtained  by  the  action 


72  III.   MONOHYDRIC  ALCOHOLS 

of  HI  and  P  on  polyhydric  alcohols,  and  these  on  hydrolysis 
yield  secondary  alcohols,  e.g.: 

C3H6(OH)3    —    C3HrI    —    C3H7.OH. 

Glycerol  s-Propyl  iodide     s-Propyl  alcohol. 

C4H6(OH)4    —    C4H9I    —    C4H9.OH. 

Erythritol  s-Butyl  iodide       s-Butyl  alcohol. 

II.  Special  Metlwds  of  Formation.  —  1.  Primary  alcohols  are 
obtained  from  aldehydes  by  reduction  with  sodium  amalgam 
and  very  dilute  sulphuric  acid  (Wurtz);   or  with  acetic  acid 
and  zinc  dust,  when  the  alkyl  acetates  are  formed  : 
CH3.CH:0+2H  =  CH3.CH2.OH. 

This  reaction  is  somewhat  similar  to  the  reduction  of  an 
olefine  to  a  paraffin.  In  both  cases  a  double  bond  is  converted 
into  a  single  bond,  and  an  atom  of  hydrogen  is  added  on  to 
each  atom  between  which  the  double  bond  originally  existed. 

Similarly  from  acid  anhydrides  (or  esters,  but  not  the  free 
acids)  and  nascent  hydrogen,  or  by  the  reduction  of  the  acid 
chlorides,  when  an  ester  of  the  alcohol  is  formed  by  the  action 
of  the  unreduced  chloride  on  the  alcohol. 

2.  Secondary  alcohols  are  formed  by  the  action  of  nascent 
hydrogen  (sodium  amalgam)  on  the  ke  tones,  CJS.^0: 

CH3.CO.CH3  +  2H  =  CH3.CH(OB>CH3. 

Pinacones  are  obtained  here  as  by-products.    (See  Ketones.) 

3.  Secondary  alcohols  are  also  formed  by  the  action  of 
aldehydes    on    dry   ethereal    solutions    of    magnesium    alkyl 
halides  (p.  120),  and  treating  the  product  which  results  with 
water  or  dilute  acid: 

CH3  •  CH  :  0  +  CH3  .  Mg  •  I  =  CH3  .  CH(OMgl)  .  CH3 

CH3  •  CH(OMgl)  .  CH3  +  H  •  OH  =  CH3  •  CH(OH)  -  CH3  +  1  •  Mg  •  OH. 

4.  Tertiary  alcohols  are  formed  by  the  action  of  (a)  ketones, 
(b)  acid  chlorides,  or  (c)  esters  of  organic  acids,  on  magnesium 
alkyl  haloids  (Grignard,  Ann.  Chem.  Phys.  1901,  24,  433),  and 
decomposing  the  products  with  water  : 

(a)  o  +  C2H6.Mg.Br      = 


(6)  CH3  -  CO  •  Cl  -f  2  CH3  •  Mg  •  I     =  (CH3)3C  -  O  -  Mgl  +  MglCl. 
(c)  CH3.C 


BEHAVIOUR  OF  THE   ALCOHOLS  73 

A  somewhat  similar  reaction  is  that  between  acid  chlorides 
and  zinc  alkyl  compounds  —  an  older  and  less  effective  method 
due  to  Butleroff. 

5.  Secondary  or  tertiary  alcohols  sometimes  ensue  by  the 
direct  combination  of  an  olefine  with  water,  e.g.  tertiary  butyl 
alcohol,  (CH3)3C«OH,  from  isobutylene.  This  often  gives  a 
simple  method  for  converting  a  primary  into  a  secondary  or 
tertiary  alcohol. 

The  Nomenclature  of  the  alcohols,  especially  of  the  secondary 
and  tertiary,  is  based  upon  a  comparison  of  them  with  methyl 
alcohol,  also  called  carbinol.  They  are  looked  upon  as  carbinol, 
CH3-OH,  in  which  the  three  hydrogen  atoms  are  wholly  or 
partially  replaced  by  alkyl  radicals,  thus:  — 

Tertiary  butyl'  alcohol,  (CH,)3C-OH  =  triraethyl  carbinol: 
Secondary  butyl  alcohol,  CH3.CH2.CH(OH).CH3, 

=  CH(OH)(CH3)(C2H6),  =  methyl-ethyl  carbinol 

The  systematic  name  of  the  alcohols  terminates  in  "ol", 
As  examples:  — 

CH3  •  CH2  •  CH2  •  CH2  •  OH  Butanol  . 

•  CH(CH3)  •  CH(OH)  •  CH3  2  :  3-Dimethylpentan-4-ol. 


Behaviour.  —  1.  The  typical  hydrogen  atom  (p.  68)  is  replace- 
able by  metals,  e.g.  readily  by  K  or  Na,  less  readily  by  Ca,  Mg, 
or  Al,  with  formation  of  alcoholates,  EtONa,  Mg(OEt)2,  &c.  : 

2  C2H6OH  +  2  Na  =  2  C2H6ONa  +  H2. 

These  react  with  water,  giving  rise  to  a  state  of  equilibrium 
as  represented  in  the  equation 

Et-ONa  +  H-OH  ^±  Et-OH  +  Na-OH. 

Briihl  (B.  1904,  37,  2066)  has  described  a  method  for  pre- 
paring the  compound  CH3  •  ONa  free  from  water  and  alcohol. 

Primary  and  secondary,  but  not  tertiary,  alcohols  combine 
with  baryta  and  lime  to  alcoholates  at  130°.  Crystalline  com- 
pounds are  formed  with  calcium  chloride,  so  that  this  salt 
cannot  be  used  for  drying  the  alcohols;  these  compounds  are 
decomposed  by  water. 

2.  They  enter  into  the  composition  of  many  compounds,  as 
"  alcohol  of  crystallization  ".     (See  pp.  75  and  79.) 

3.  They  react  with  acids  both  mineral  and  organic  in  some- 


74  III.   MONOHYDRIC  ALCOHOLS 

•what  the  same  manner  as  metallic  hydroxides  do,  yielding 
'-alkyl  salts  or  esters  and  water  (cf.  Esterification) : 

CH3.COOH  =  CH3.COOK  +  H2O, 

Acetic  acid. 

OOH  ^±  CH3.COOC2H5  +  H20. 

The  methyl  and  ethyl  esters  derived  from  certain  substituted 
benzole  acids,  e.g.  paranitrobenzoic  acid,  N02  •  C6H4  •  C02H,  are 
solids  with  definite  melting-points,  and  are  sometimes  used  in 
identifying  small  amounts  of  these  alcohols. 

4.  Dehydrating  agents  convert  them  into  defines. 

5.  With   halogen    hydracids   or  phosphorus   halides,   they 
yield  monohalide  derivatives  of  the  hydrocarbons  (p.  58). 

6.  For  the  behaviour  of  primary,  secondary,  and  tertiary 
alcohols  upon  oxidation,  see  p.  68  et  seq. 

Methyl  alcohol  is  oxidized  to  carbon  dioxide  as  the  primary 
product  (formic  acid)  is  itself  readily  oxidized. 

7.  The  primary,  secondary,  and  tertiary  alcohols  can  also  be 
distinguished  from  one  another  by  the  behaviour  of  the  nitro 
compounds,  which  are  formed  by  the  action  of  silver  nitrite 
on  the  iodides  (cf.  Meyer  and  Jacobson,  I,  p.  221). 

8.  Halogens  do  not  substitute  but  oxidize. 

9.  Many  alcohols  when  heated  with  excess  of  soda  lime 
yield  the  sodium  salts  of  the  corresponding  acids. 

Methyl  alcohol,  Methanol,  Wood  Spirit,  CH3OH,  was'  dis- 
covered in  wood-tar  by  Boyle  in  1661,  and  its  difference  from 
ordinary  alcohol  recognized  in  1812  by  Phillips  Taylor.  Its 
-composition  was  established  in  1834  by  Dumas  and  Peligot. 
It  occurs  as  methyl  salicylate  in  Gaultheria  pivcumbens  (oil  of 
winter  green,  Canada),  as  butyric  ester  in  the  unripe  seeds  of 
Heradeum  giganteum,  and  as  ester  of  benzoylecgonin  in  cocain. 

Formation. — 1.  By  chlorinating  methane,  CH4,  and  hydro- 
lysing  the  resulting  methyl  chloride  (Berthelot}.  Methyl  iodide 
may  be  hydrolysed  in  a  similar  manner. 

2.  By  the  destructive  distillation  of  wood  (beech  wood)  at 
about  350°. 

By  this  distillation  there  are  obtained  (a)  Gases  (CH4,  C2H6, 
C2H4,  C2H2,  C3H6,  C4H8,  CO,  C02,  H2).  (b)  An  aqueous  dis- 
tillate of  " pyroligneous  acid",  containing  methyl  alcohol  (1-2 
per  cent),  acetic  acid  (10  per  cent),  acetone  (0-1-0-5  per  cent), 
methyl  acetate,  allyl  alcohol,  &c.  (c)  Wood-tar,  containing  para- 
ffins, naphthalene,  phenol,  guaiacols,  &c.  (d)  Wood  charcoal. 

3.  Also  by  the  dry  distillation  of  vinasse. 


ETHYL  ALCOHOL  75 

It  is  prepared  commercially  from  the  crude  pyroligneous- 
acid  by  repeated  distillation  after  neutralization  with  lime, 
and  is  purified  by  formation  of  the  CaCl2  compound,  which 
is  a  solid,  and  stable  at  100°;  or,  better,  by  transformation  into 
the  oxalic  or  benzoic  ester,  both  of  which  are  easy  to  purify 
and  hydrolyse. 

Properties. — It  is  a  colourless  liquid,  boils  at  66°,  and  has  a 
specific  gravity  about  O8.  The  alcohol  of  commerce  usually 
contains  acetone.  It  burns  with  a  non-luminous  flame,  dis- 
solves fats,  oils,  &c.,  and  acts  as  an  intoxicant  like  ethyl 
alcohol.  It  also  enters  into  the  composition  of  compounds  as 
"alcohol  of  crystallization",  e.g.  BaO  +  2CH40;  MgCL + 
6CH40;  CaCl2  +  4  CH4O  (six-sided  plates).  It  is  readily 
oxidized  to  formic  aldehyde  and  formic  acid,  being  also  con- 
verted into  the  latter  when  heated  with  soda-lime.  Potassium 
methoxide,  CH3OK,  is  a  white  crystalline  powder,  and  forms 
a  definite  crystalline  compound  CH3OK  -f  CH3OH. 

The  anhydrous  alcohol  dissolves  a  small  amount  of  dehy- 
drated cupric  sulphate  to  a  blue -green  solution.  Distilled 
over  heated  zinc  dust,  it  decomposes  almost  quantitatively 
into  CO  +  2  H2. 

Uses. — For  tar  colours  —  (also  as  CH3I  and  CH3C1);  as 
methyl  ether  in  the  manufacture  of  ice;  for  polishes  and  var- 
nishes; as  Wiggersheim's  preservative  liquid;  for  methylating 
spirits  of  wine,  &c. 

Ethyl  alcohol,  Ethanol,  Spirits  of  Wine,  C2H5OH.  Liquids 
containing  spirits  of  wine  have  been  known  from  very  early 
times,  and  their  concentration  either  by  distillation  or  by 
dehydration  with  carbonate  of  potash  is  also  an  old  art.  We 
read  of  it  as  "  alcohol "  in  the  sixteenth  century.  Lavoisier 
arrived  at  the  qualitative,  and  de  Saussure  in  1808  the  quanti- 
tative composition  of  alcohol. 

In  the  vegetable  kingdom  alcohol  is  only  found  occasionally, 
as  ethyl  butyrate,  but  in  the  animal  kingdom  it  occurs  in 
various  forms,  e.g.  in  diabetic  urine.  It  is  also  present  in 
small  quantity  in  coal-tar,  bone  oil,  wood  spirit,  and  bread, 
fresh  English  bread  containing  0'3  per  cent. 

Formation. — 1.  From  C2H6  by  conversion  into  C2H5C1  and 
hydrolysis  of  the  latter  according  to  modes  of  formation  1 
and  2. 

2.  Ethylene  and  concentrated  H2S04  react  at  160°,  yielding 
ethyl  hydrogen  sulphate, 

C2H4  +  H2S04  =  C2H5HS04; 


76  III.    MONOHYDRIC  ALCOHOLS 

and  this  when  boiled  with  water  gives  ethyl  alcohol.     (See 
pp.  44  and  70.)     This  method  was  discovered  by  Faraday,  and 
corroborated  in  1855  by  Berthelot. 
3.  By  the  reduction  of  acetaldehyde 

CH3.CH:O  +  2H  =  CH3.CH2-OH. 


4.  Preparation  by  the  Alcoholic  Fermentation  of  Sugar.  —  Directly 
from  grape  and  fruit  sugars,  C6H1206,  and  indirectly  from  cane- 
sugar,  C^H^Ojp  after  previous  hydrolysis  to  two  molecules  of 
C6H1206;  also  indirectly  from  malt-sugar,  from  starch,  &c. 

Fermentations  are  peculiarly  slow  decomposition-processes  of 
organic  substances  which  are  accompanied,  as  a  rule,  with  libera- 
tion of  gas  and  evolution  of  heat,  and  which  are  induced  by 
micro-organisms,  or  by  complex  organic  nitrogenous  substances 
(enzymes)  of  animal  or  vegetable  origin.  The  alcoholic  fer- 
mentation of  sugar,  i.e.  the  fermentation  which  produces  spirit, 
is  caused  by  the  varieties  of  the  genus  Saccharomyces,  the  yeast 
ferment,  which  forms  small  oval  microscopic  cells,  multiplying 
by  gemmation.  As  plants,  these  require  for  their  sustenance 
inorganic  salts,  e.g.  phosphates,  potassium  salts,  and  nitrogen 
in  the  form  of  ammonium  salts,  but,  as  non-assimilating  fungi, 
no  carbon  dioxide. 

In  the  vinous  fermentation  94  to  95  per  cent  of  the  sugar 
breaks  up  into  alcohol  and  carbon  dioxide, 

C6H1206  =  2C2H60  +  2C02, 

with  2-5  to  3-6  per  cent  glycerol,  C3H5(OH)3,  and  0'4  to  0*7 
per  cent  succinic  acid,  C4H604,  as  invariable  by-products.  In 
addition  to  these,  most  of  the  higher  homologues  of  ethyl 
alcohol  are  also  formed  —  the  so-called  fusel  oil  —  the  latter  re- 
sulting largely  from  the  presence  of  foreign  micro-organisms. 

The  chief  constituent  of  fusel  oil  is  fermentation  amyl 
alcohol  (isobutyl  carbinol),  C5HnOH,  but  it  has  also  been 
proved  to  contain  the  two  propyl  alcohols  (chiefly  isopropyl), 
normal,  iso,  and  tertiary  butyl  alcohols,  normal  and  active 
amyl  alcohols,  together  with  higher  homologues  and  esters. 
They  can  be  separated  by  means  of  their  hydrobromic  esters. 

Conditions  of  Fermentation.  —  Fermentation  can  only  go  on 
between  the  limits  of  3°  and  35°,  the  most  favourable  tempera- 
ture being  between  25°  and  30°.  The  solution  must  not  be 
too  concentrated,  as  the  organism  cannot  live  in  a  solution  of 
alcohol  of  greater  concentration  than  14  per  cent;  the  presence 
of  air  is  not  strictly  necessaiy,  but  it  has  a  favouring  influence, 


ALCOHOLIC  FERMENTATION  77 

Yeast  loses  its  activity  upon  the  addition  of  any  reagents 
which  destroy  the  cells,  also  when  it  is  thoroughly  dried, 
when  heated  to  60°,  when  treated  with  alcohol,  acids,  and 
alkalis;  the  addition  of  small  quantities  of  salicylic  acid, 
phenol,  corrosive  sublimate,  &c.,  also  prevents  fermentation. 

For  a  number  of  years  it  was  thought  that  the  presence  of 
the  living  yeast  plant,  or  of  some  other  similar  organism,  was 
essential  for  the  production  of  alcoholic  fermentation.  The 
recent  work  of  E.  Buchner  (B.  1897,  32,  2086,  2372;  1898, 
33,  971,  2764)  has  shown  that  the  fermentation  is  brought 
about  by  an  enzyme  called  Zymase,  which  is  contained  in  the 
cell.  If  the  yeast  cells  are  crushed  with  "  Kieselgiihr "  (a 
siliceous  earth)  and  water,  so  that  the  cell  walls  are  broken, 
and  the  mass  then  filtered  through  a  Chamberland  filter  under 
considerable  pressure,  an  extract  is  obtained  which,  although 
practically  free  from  yeast  cells,  can  yet  induce  alcoholic  fer- 
mentation. The  zymase  is  relatively  unstable  and  easily  de- 
composed, e.g.  when  the  solution  is  heated  or  even  kept  for 
some  time,  but  it  may  be  preserved  by  the  addition  of  certain 
antiseptic  substances,  such  as  chloroform,  thymol,  &c.,  which 
readily  kill  the  yeast  plant  itself.  (Compare  Chap.  XL VIII.) 

Buchner's  researches  indicate  that  fermentations  induced  by 
organized  ferments  are  probably  due  to  certain  unorganized 
ferments  (enzymes)  contained  in  the  cells  of  the  organism. 

The  following  materials  are  used  for  the  preparation  of 
alcohol  or  of  liquids  containing  alcohol: — 

(a)  Grape-sugar,  fruit-sugar,  i.e.  grapes  and  other  ripe  fruits, 
for  wine,  &c.  (b)  Cane  or  beet  sugar  and  molasses  for  brandy. 
Solutions  of  cane-sugar  are  fermented  by  yeast,  since  ordinary 
yeast  always  contains  small  amounts  of  an  enzyme  (invertase), 
which  can  hydrolyse  cane-sugar  to  glucose  and  fructose : 

C12H22On  +  H20  =  C6H1206  +  C6H1206, 

and  these  are  then  directly  fermented  by  the  yeast  organism, 
(c)  The  starch  of  cereals  for  beer  and  corn  brandy,  and  of 
potatoes  for  potato  brandy.  The  starch  is  first  converted  into 
malt-sugar  and  dextrine  under  the  influence  of  diastase,  or 
into  grape-sugar,  by  boiling  with  dilute  acids,  and  these  sugars 
are  then  fermented. 

The  transformation  of  starch  into  malt-sugar  (maltose)  and 
dextrine  is  a  typical  example  of  fermentation  by  an  enzyme, 
the  special  enzyme  in  this  case  being  diastase,  a  complex  organic 
nitrogen  derivative  produced  during  the  germination  of  the 


78  III.    MONOHYDRIC  ALCOHOLS 

barley  in  the  process  of  malting.  The  transformation  of  the 
starch  into  maltose,  &c.,  is  in  reality  a  process  of  hydrolysis 
induced  by  the  ferment.  The  maltose  C12H22On  in  its  turn 
is  hydrolysed  by  a  second  ferment  (maltose)  to  grape-sugar, 
CpHi206,  which  is  then  transformed  into  alcohol  and  carbon 
dioxide. 

A  wine  of  medium  strength  contains  8J  to  10  per  cent 
alcohol,  port  wine  15  per  cent,  sherry  up  to  21  per  cent, 
champagne  8  to  9  per  cent,  and  beer  an  average  of  2  to  6 
per  cent. 

The  different  varieties  of  brandy  or  spirits  obtained  by 
"  burning ",  i.e.  by  distilling  fermented  liquids,  contain  30  to 
40  per  cent  alcohol,  and  cognac  even  over  50  per  cent. 

Purification  of  alcohol.  It  is  difficult  to  separate  alcohol 
completely  from  water  by  distillation,  since  their  boiling-points 
are  only  22°  apart  from  one  another.  Even  after  repeated 
rectification  the  distillates  are  found  to  contain  water.  The 
same  reason  applies  to  the  difficulty  of  separating  alcohol  from 
its  higher  homologues  (fusel  oil).  From  an  alcohol  containing 
30  per  cent  of  water  the  fusel  oil  can  be  extracted  by  chloro- 
form. 

On  the  large  scale  this  separation  is  excellently  effected  by 
the  use  of  dephlegmators  or  fractionating  columns,  which  are 
based  upon  the  principle  of  partial  volatilization  and  partial 
cooling  of  the  vapours  (Adam  and  JBerard;  improved  by  Savalle, 
Pistorius,  Coffey,  and  others).  In  this  way  an  alcohol  containing 
98  to  99  per  cent  can  be  obtained. 

Aqueous  alcohol  can  be  deprived  of  the  greater  part  of  its 
water  by  the  addition  of  strongly  heated  carbonate  of  potash 
or  anhydrous  copper  sulphate,  or  by  distillation  over  quick- 
lime, and  the  last  portions  can  be  extracted  by  baryta,  or  by 
several  additions  of  metallic  calcium  and  repeated  distillation. 
Alcohol  containing  water  becomes  turbid  on  being  mixed  with 
benzene,  carbon  bisulphide,  or  liquid  paraffin  oil,  and  it  gives 
a  white  precipitate  of  Ba(OH)2  on  the  addition  of  a  solution 
of  BaO  in  absolute  alcohol,  and  is  capable  of  restoring  the 
blue  colour  to  anhydrous  copper  sulphate.  Alcohol  free  from 
water  is  termed  absolute  alcohol.  Ordinary  absolute  alcohol 
usually  contains  at  least  0*2  per  cent  of  water.' 

Contraction  takes  place  on  mixing  alcohol  and  water 
together,  53-9  volumes  alcohol  +  49 -8  volumes  water  giving, 
not  103-7,  but  100  volumes  of  the  mixture.  The  percentage 
pf  alcohol  in  any  spirit  is  determined  either  from  its  specific 


PROPERTIES   OF  ALCOHOL  79 

gravity  by  reference  to  a  specially -calculated  table,  or  by 
areometers  of  particular  construction,  or  by  its  vapour  tension 
as  estimated  by  Geissler's  vaporimeter. 

Properties. — It  is  a  colourless  mobile  liquid  with  character- 
istic spirituous  odour;  boils  at  78-3°,  or  at  13°  under  21  mm. 
mercury  pressure.  Solidifies  at  •— 112'3°,  and  has  sp.  gr.  0*79 
at  15°.  It  burns  with  an  almost  non- luminous  flame,  is 
exceedingly  hygroscopic,  and  miscible  with  water  and  with 
ether  in  all  proportions.  Forms  several  cryo-hydrates  with 
water  (  +  12Aq.,  +  3Aq.,  -j-JAq.).  Is  an  excellent  solvent 
for  many  organic  substances  such  as  resins  and  oils,  and  also 
dissolves  sulphur,  phosphorus,  &c.,  to  some  extent.  With 
concentrated  sulphuric  acid  it  yields,  according  to  the  con- 
ditions, ethyl  hydrogen  sulphate,  ether,  or  ethylene.  It  dif- 
fuses through  porous  membranes  into  a  dry  atmosphere  more 
slowly  than  water,  and  coagulates  albumen,  being  therefore 
used  for  preserving  anatomical  preparations. 

It  is  very  readily  oxidized  by  the  oxygen  of  the  air,  either 
in  presence  of  finely-divided  platinum  or  in  dilute  solutions 
in  presence  of  certain  ferments,  first  to  aldehyde  and  then  to 
acetic  acid;  thus,  beer  and  wine  become  sour,  but  not  the 
pure  alcohol  itself.  K2O2Or  or  Mn02  +  H2S04  oxidize  it 
in  the  first  instance  to  aldehyde;  fuming  nitric  acid  attacks 
it  with  explosive  violence,  yielding  numerous  products;  but, 
by  the  action  of  colourless  concentrated  HN03,  ethyl  nitrate 
can  be  obtained  under  suitable  conditions;  in  dilute  solution 
glycollic  acid  is  formed.  Alkalis  also  induce  a  gradual 
oxidation  in  the  air;  thus,  alcoholic  potash  or  soda  solutions 
quickly  become  brown  with  formation  of  aldehyde  resin,  this 
latter  resulting  from  the  action  of  the  alkali  upon  the  alde- 
hyde first  produced.  Alcoholic  potash  therefore  frequently 
acts  as  a  reducing  agent,  e.g.  upon  aromatic  nitro-compounds. 
(See  these.)  Chlorine  and  bromine  first  oxidize  alcohol  to 
aldehyde  and  then  act  as  substituents.  (See  Chloral.) 
Chlorinated  alcohols  can  therefore  only  be  prepared  indirectly 
(cf.  Ethylene  chlorhydrin).  When  the  vapour  of  alcohol  is 
led  through  a  red-hot  tube,  H,  CH4,  C2H4,  C2H2,  CgHg,  C10H8, 
CO,  C2H40,  C2H402,  &c.,  are  formed. 

Of  the  compounds  containing  alcohol  of  crystallization  may 
be  mentioned,  KOH  +  2  C2H60,  LiCl  +  4  C2H60,  CaCl2 
+  4C2H60,  and  MgCl2  +  6C2H6O. 

Sodium  ethoxide,  C2H5ONa,  is  of  special  importance  among 
the  alcoholates.  It  is  formed  by  the  action  of  sodium  upon 


80  III.    MONOHYDRIC  ALCOHOLS 

absolute  alcohol.  The  crystals  of  C2H5-ONa  +  2  C2H60,  at 
first  obtained,  lose  their  alcohol  of  crystallization  at  200°  and 
change  into  a  white  powder  of  C2H5ONa.  (See  also  Bruhl.) 
Sodium  ethoxide  is  of  especial  value  for  syntheses,  and  can 
frequently  be  employed  in  alcoholic  solution.  This  compound 
is  sometimes  termed  sodium  ethylate,  but  the  better  name  is 
ethoxide,  in  order  to  indicate  its  close  relationship  to  sodium 
hydroxide,  NaOH. 

When  taken  in  small  quantity  alcohol  acts  as  a  stimulant, 
in  larger  quantity  as  an  intoxicant.  Absolute  alcohol  is 
poisonous,  and  quickly  causes  death  when  injected  into  the 
veins.  The  presence  of  considerable  amounts  of  fusel  oil  has 
detrimental  physiological  effects. 

Detection  of  Alcohol. — 1.  By  the  iodoform  reaction*  (see  lodo- 
form),  when  1  part  in  2000  of  water  can  be  recognized. 

2.  By  means  of  benzoyl  chloride,  CgH5COCl,  which  yields 
with  alcohol  the  characteristically  smelling  ethyl  benzoate;  or 
of  jp-nitrobenzoyl  chloride,  which  yields  ethyl  ^?-nitrobenzoate 
melting  at  57°;  the  corresponding  methyl  ester  melts  at  97°. 

Propyl  alcohols,  C3H7OH. 

1.  Normal  propyl  alcohol,  1-Propanol,  CH3 .  CH2 .  CH2  •  OH 
(Chancel,  1853),  is  obtained  from  fusel  oil  by  means  of  its 
hydrobromic  ester  (Fittig),  or  directly  by  fractionation.  It 
has  also  been  obtained  from  propionic  aldehyde  and  propionic 
anhydride  by  reduction  with  sodium  amalgam  (Rossi).  It  is 
a  liquid  with  a  pleasant  spirituous  odour,  and  boils  19°  higher 
than  ethyl  alcohol.  It  is  miscible  with  water  in  all  propor- 
tions, but  may  be  salted  out  on  addition  of  calcium  chloride. 
Its  constitution  follows  from  that  of  propionic  acid,  into  which 
it  is  converted  on  oxidation. 

Of  the  higher  alcohols,  w-butyl  alcohol,  CH8.CH2.CH2. 
CH2'OH,  may  be  obtained  from  the  fusel  oil  formed  when 
certain  special  species  of  yeast  (Saccharomyces  ellipsoidius)  are 
used  in  the  alcoholic  fermentation. 

Isobutyl  carbinol,  (CH3)2:CH.CH2.CH2.OH,  is  the  chief 
constituent  of  the  so-called  "  fermentation  amyl  alcohol " 
obtained  by  fractional  distillation  of  fusel  oil,  the  other  con- 
stituent being  secondary  butyl  carbinol, 

C2H6.CH(CH3).CH2.OH. 
This  latter,  on  account  of  its  action  on  polarized  light,  is 

*  Acetaldehyde,  acetone,  and  isopropyl  alcohol  also  givo  this  reaction, 
but  not  methyl  alcohol. 


MONOHYDRIC  UNSATURATED   ALCOHOLS  81 

fenerally  known  as  active  (i.e.  optically  active)  amyl  alcohol, 
b  is  Isevo-rotatory,  i.e.  rotates  the  plane  of  polarization  to  the 
left  (cf.  active  valeric  acid),  and  has  [a]D  —5 '9°  at  20°. 

Normal  hexadecyl- alcohol,  or  cetyl  alcohol,  forms  as 
palmitic  ester  the  chief  constituent  of  spermaceti.  The  cetyl 
alcohol  of  commerce  contains,  in  addition,  a  homologous  alco- 
hol, C18H380. 

Ceryl  alcohol,  Cerotin,  C26H63OH,  forms  as  cerotic  ester 
Chinese  wax. 

Melissic,  or  miricyl  alcohol,  C30H61OH  or  C31H63OH,  is 
present  as  palmitic  ester  in  bees'-wax  and  in  Carnauba  wax, 
and  is  most  conveniently  prepared  from  the  latter.  The 
alcohols  are  obtained  from  all  these  esters  (wax  varieties)  by 
hydrolysis  with  boiling  alcoholic  potash. 

B.  Monohydrie  Unsaturated  Alcohols,  CnH^OH 

These  are  very  similar  to  the  saturated  alcohols  both  in 
physical  properties  and  in  general  chemical  behaviour,  but  are 
sharply  distinguished  from  the  latter  by  the  formation  of  addi- 
tive compounds  with  hydrogen,  halogens,  halogen  hydracids, 
&c.5  e.g.-. 

CH2 :  CH  •  CH2  •  OH  +  Br2  =  CH2Br  •  CHBr  •  CH2  •  OH. 

They  thus  resemble  the  olefines  owing  to  the  presence  of  a 
double  bond,  and  the  products  are  saturated  alcohols  or  their 
halide  derivatives,  the  latter  of  which  cannot  be  prepared 
directly  by  substitution  of  the  alcohols.  These  unsaturated 
alcohols  are  to  be  considered  as  olefines  in  which  an  atom  of 
hydrogen  is  replaced  by  hydroxyl. 

According  to  theory,  the  existence  of  alcohols  which  contain 
the  hydroxy-methylene  group,  :CH(OH),  linked  to  a  Carbon 
atom  by  a  double  bond,  might  be  predicted.  To  this  class 
belongs"  vinyl  alcohol  (ethenol),  CH:CH-OH,  which  occurs 
in  commercial  ether,  but  which  has  not  yet  been  isolated 
(B.  22,  2863),  although  derivatives  of  it  are  known.  By  the 
reactions  in  which  one  would  expect  it  to  be  formed,  its 
isomer,  CH3.CHO  (acetaldehyde),  is  formed;  in  fact,  the 
grouping  :C:CH-OH  is  usually  unstable,  passing  as  it  does 
into  the  more  stable  one,  :CH-CH:0,  a  transformation  which 
is  most  readily  explained  upon  the  assumption  that  water  is 
taken  up  and  again  split  off.  Similarly,  instead  of  the  group 
CH2:C(OH).CH3,  we  always  get  CH3.CO.CH3. 

(  B  480  ) 


82  III.   MONOHYDRIC  ALCOHOLS 

Allyl  alcohol  (l-Propene-3-ol),  CH2:CH.CH2OH  (Cahours 
and  Hofmann,  1856),  is  present  to  the  extent  of  O'l  to  0'2  per 
cent  in  wood  spirit,  and  is  formed  (1)  from  allyl  iodide;  (2)  by 
reduction  of  its  aldehyde,  acrolein  (see  this);  (3)  by  heating 
glycerol,  C3H5(OH)3,  with  oxalic  or  formic  acid  and  a  little 
ammonium  chloride  to  220°.  The  reaction  is  somewhat 
similar  to  the  production  of  formic  acid,  and  in  both  cases 
the  same  product  is  first  formed,  viz.  glyccryl  monoformate — 

CH2-OH          CH2.OH  CH2.OH 

CH-OH    —  CH.:OH  j  —  CH 

/"YD"       ^\TT  ^ITT     '     /~\  "/"V^     'TT*  /^ITT 

V^Jj-2  *  vy-CL  ^-^-2  •  *  ^  *  v/w  • ; Jtl;  V^±i2j 


and  this  when  heated  to  the  required  temperature,  220°, 
decomposes  into  C02,  H20,  and  allyl  alcohol.  Allyl  alcohol 
is  a  mobile  liquid  of  suffocating  smell,  having  almost  the  same 
boiling-point  (97°)  as  rc-propyl  alcohol;  like  the  latter,  it  is 
miscible  with  water.  It  does  not  take  up  nascent  hydrogen 
directly,  but  chlorine,  bromine,  cyanogen,  hypochlorous  acid, 
&c.  If  cautiously  oxidized,  it  yields  glycerol,  but  stronger 
3xidation  converts  it  into  its  aldehyde.,  acrolein,  and  acid, 
acrylic  acid,  containing  the  same  number  of  carbon  atoms, 
and  it  is  therefore  a  primary  alcohol;  hence  the  above  con- 
stitutional formula. 

C.  Monohydrie  Unsaturated  Alcohols,  Cyi^.g.OH 

These  alcohols  are  derivatives  of  acetylene  and  its  homo- 
logues.  The  compounds  possess: — (1)  The  characteristic  pro- 
perties of  alcohols.  (2)  The  properties  of  unsaturated  com- 
pounds. Each  molecule  of  such  an  alcohol  can  combine  with 
1  or  2  molecules  of  a  halogen  or  halogen  hydracid.  (3)  Most 
of  them  possess  the  further  peculiarity  of  forming  explosive 
compounds  with  ammoniacal  copper  and  silver  solutions, 
e.g.  C3H2AgOH,  the  former  being  coloured  yellow  and  the 
latter  white;  acids  decompose  these  compounds  into  the  un- 
saturated alcohol.  Those  of  them  which  do  not  yield  such 
metallic  compounds  contain,  not  a  triple  bond,  but  two  double 
ones  between  the  carbon  atoms.  The  most  important  of  these 
alcohols  is — 

Propargyl  alcohol,  OT  propinyl  alcohol  (l-Propin-3-ol)t 

C3H3OH,  =  CH-C-CHsOH, 


ETHERS  83 

a  mobile  liquid  of  agreeable  odour,  lighter  than  water,  and 
boiling  at  114°,  i.e.  somewhat  higher  than  normal  propyl 
alcohol. 

For  further  examples  of  unsaturated  alcohols,   see  Open- 
chain  Terpenes  (Chap.  XLI,  A). 


IV.   DERIVATIVES  OF  THE  ALCOHOLS 

These  may  be  classed  in  the  following  divisions  :  _ 

A.  Ethers  of  the  alcohols,  or  alkyl  oxides,  e.g.  C2H5.0«C2H5, 
ethyl  ether. 

B.  Thio-alcohols  and  ethers,  or  alkyl  hydrosulphides  and 
sulphides,  e.g.  C2H5-SH  and  (C2H5)2S. 

C.  Nitrogen  bases  of  the  alcohol  radicals. 

D.  Other  metalloid  compounds  of  the  alcohol  radicals. 

E.  Metallic  compounds  of  the  alcohol  radicals,  or  organo- 
metallic  compounds. 

A.  Ethers  Proper  (Alkyl-  or  Alphyl-Oxides) 

The  ethers  of  the  monohydric  alcohols  are  compounds  of 
neutral  character  derived  from  the  alcohols  by  elimination  of 
the  elements  of  water  (1  molecule  water  from  2  molecules 
alcohol).  They  can  frequently  be  prepared  by  treating  the 
alcohols  with  sulphuric  acid,  and  are  distinguished  from  the 
latter  by  not  reacting  with  acids  to  form  esters,  and  by  being 
substituted  and  not  oxidized  by  the  halogens,  &c.  Only  the 
lowest  member  of  the  series  is  gaseous,  most  of  them  are 
liquid,  and  the  highest  are  solid.  The  more  volatile  ethers 
are  characterized  by  a  peculiar  odour  which  is  not  shown  by 
the  higher  members. 

Constitution.  —  The  hydrogen  atoms  cannot  be  replaced  by 
sodium  or  other  metallic  radicals  (see  p.  18),  and  are  all 
presumably  attached  to  carbon. 

Their  structure  as  alkyl  oxides,   or  anhydrides  of  mono- 
hydric  alcohols   (cf.    metallic   oxides),    follows   largely   from 
modes  of  formation  2  and  3,  from  the  non-reactive  character 
of  the  hydrogen  atoms,  and  from  reactions  4  and  5,  p.  85. 
K;OH  C2H5OH  _  C2H5^ 

c2H6o;n  -       ^° 


The  alkyl   groups  contained  in  them  may  either  be  the 
same,  as  in  ordinary  ether  and  in  methyl  ether,  (CH3)20,  in 


84  IV.   DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 

which  case  they  are  termed  "simple  ethers";  or  they  may  be 
different,  as  in  methyl-ethyl  ether,  CH3-0'C2H5,  when  they 
are  known  as  "mixed  ethers". 

Ethers  derived  from  tertiary  alcohols  are  not  known. 

Modes  of  Formation.  —  1.  By  heating  the  alcohols,  CnH2n+1«OH, 
with  sulphuric  acid.  The  reaction  proceeds  in  two  phases,  e.g.: 

(a)  C2H5.OH  +  OH-S02.OH       =  OH.S02.OC2H5  +  H-OH. 
(6)  OH.S02.OC2H6+C2H5.OH  =  OH.S02.OH 


In  phase  a  an  alkyl  hydrogen  sulphate  is  formed,  which, 
when  further  heated  with  alcohol,  as  in  b,  yields  ether  and 
regenerates  sulphuric  acid.  The  latter  is  therefore  free  to 
work  anew,  and  in  this  way  to  convert  a  very  large  quantity 
of  alcohol  into  ether. 

This  process  is  theoretically  a  continuous  one,  but  practi- 
cally it  has  its  limits,  through  secondary  reactions,  such  as  the 
formation  of  S02,  &c.  A  modification  of  the  method  consists 
in  heating  the  alcohol  with  benzene  -  sulphonic  acid  C6H5» 
S02»OH  in  place  of  sulphuric  acid.  No  sulphur  dioxide  is 
formed,  and  the  reaction  becomes  in  reality  continuous.  The 
method  is  only  suitable  for  primary  alcohols;  secondary  and 
tertiary  under  similar  conditions  yield  defines.  Hydrochloric, 
hydrobromic,  and  hydriodic,  among  other  acids,  act  similarly  tc 
sulphuric  acid;  thus  ether  is  obtained  when  alcohol  is  heated 
with  dilute  hydrochloric  acid  in  a  sealed  tube  to  180°,  ethyl 
chloride,  C2H5C1,  being  formed  as  an  intermediate  product 
When  alcohol  is  heated  with  hydrochloric  acid,  a  state  of 
equilibrium  is  established  between  the  alcohol,  ether,  ethyl 
chloride,  hydrochloric  acid,  and  water,  after  which  the  same 
quantity  of  each  of  these  products  is  destroyed  as  is  formed 
in  unit  of  time. 

2.  By  the  action  of  alkyl  halides  on  sodium  -alky  late,  or 
also  upon  alcoholic  potash: 


3.  From  alkyl  halides  and  dry  silver  oxide,  Ag20  (also  HgO 
andNa20): 

2C2H6I 


Modes  of  formation  1  and  2  yield  mixed  as  well  as  simple 
ethers,  e.g.: 


C2H6.S04H  +  CH3-OH  =  C2H5.O.CH,  +  H9S04. 
CVEUI  +  CH3  •  ONa          =  C6HU .  O  •  CH3  -f  Nal. 


ETHYL  ETHER  85 

Properties.  —  1.  The  ethers  are  very  stable,  e.g.  ammonia, 
alkalis,  dilute  acids,  and  metallic  sodium  have  no  action  upon 
them,  nor  has  phosphorus  pentachloride  in  the  cold. 

2.  When  superheated  with  water  in  presence  of  some  acid, 
such  as  sulphuric,  the  ethers  take  up  water  and  are  retrans- 
formed  into  alcohols,  the  secondary  more  readily  than  the 
primary;    this  change  also  proceeds,  but   extremely  slowly, 
at  the  ordinary  temperature. 

3.  When  warmed  with  concentrated  sulphuric  acid,  alcohol 
and  ethyl  hydrogen  sulphate  are  formed  : 


.OH  +  C2H6.HS04. 

4.  When  saturated  with  hydriodic  acid  gas  at  0°,  the  ethers 
yield  alcohol  and  alkyl  iodide  : 

C2H6.O.C2H5  +  HI  =  C2H6.OH  +  C2H6L 

When  the  ethers  are  "  mixed  ",  the  iodine  attaches  itself  to 
the  smaller  alkyl  group;  further  interaction  yields,  of  course, 
two  molecules  of  alkyl  iodide. 

5.  When  heated  with  phosphorus  halides  the  oxygen  atom 
is  replaced  by  two  halogen  atoms,  and  two  molecules  of  an 
alkyl  halide  are  formed. 

6.  Like  the  alcohols,  the  ethers  are  oxidized  by  nitric  and 
chromic  acids,  but  halogens  substitute  in  them  and  do  not 
oxidize;  in  this  latter  respect  they  resemble  the  hydrocarbons. 

7.  Many  ethers  form  definite  compounds  with  acids,  especially 
complex  acids  like  H4FeC6N6  (B.  190-1,  34,  2688);  also  with 
bromine,  with  metallic  salts,  &c.  (J.  C.  S.  1904,  85,  1106;  Proc. 
1904,  165). 

Ethyl  ether,  Ethane-oxy-ethane,  "Ether"  (C2H5)20,  was  dis- 
covered by  Valerius  Cordus  about  1544,  and  possibly  before 
that  time  by  Raymond  Lully.  It  was  also  called  "  sulphuric 
ether  ",  and  "  vitriol  ether  ",  on  account  of  its  being  supposed 
to  contain  sulphur.  Its  composition  was  established  by  Saus- 
sure  in  1807,  and  Gay-lMssac  in  1815, 

Preparation.  —  By  the  continuous  process  from  ethyl  alcohol 
and  sulphuric  acid  at  140°,  with  gradual  addition  of  the 
alcohol,  according  to  Boullay.  It  is  freed  from  alcohol  by 
shaking  with  water,  and  dried  by  distillation  over  lime  or 
calcium  chloride,  and  finally  over  metallic  sodium. 

Theories  of  the  Formation  of  Ether.—  At  first  the  action  of  the 
sulphuric  acid  was  considered  to  consist  in  an  abstraction  of 
water.  Later  on,  it  was  thought  that  the  acid  gave  rise  to 


86  IV.  DERIVATIVES  OF  MONOHYDRIC  ALCOHOLS 

a  contact  action  (Mitscherlich,  Berzelius),  but  Liebig  showed 
that  this  view  was  incorrect,  since  ethyl  hydrogen  sulphate  is 
formed.  Liebig  assumed  that  the  ethyl  hydrogen  sulphate 
decomposed,  when  heated,  into  ether  and  S03;  but  Graham,  on 
the  other  hand,  proved  that  the  acid  gives  no  ether  when 
heated  alone  to  140°,  but  only  when  heated  along  with  more 
alcohol. 

After  this,  Williamson  propounded  the  theory  of  etheri- 
fication  at  present  held,  a  theory  based  on  the  opinion  of 
Laurent  and  Gerhardt  that  ether  contains  two  ethyl  radicals. 
Its  correctness  was  proved  by  mode  of  formation  2,  and  also 
by  the  preparation  of  mixed  ethers. 

Properties. — It  is  a  mobile  liquid  with  powerful  ethereal 
odour,  and  is  very  volatile,  even  at  the  ordinary  temperature. 
It  melts  at  -113°,  boils  at  +  34'9°,  has  specific  gravity  =  0'72 
at  17 '4°,  and  at  120°  has  a  vapour  pressure  of  10  atmospheres. 
It  produces  considerable  lowering  of  temperature  when  evapo- 
rated. It  is  easily  inflammable,  and  therefore  dangerous  as  a 
cause  of  fire,  from  the  dissemination  of  its  very  heavy  vapour; 
a  mixture  of  it  with  oxygen  or  air  is  explosive.  It  is  some- 
what soluble  in  water  (1  part  in  10),  and,  conversely,  3  volumes 
of  water  dissolve  in  100  volumes  of  ether;  the  presence  of 
water  can  be  detected  by  the  milkiness  which  ensues  upon  the 
addition  of  carbon  disulphide.  Ether  is  an  excellent  solvent 
or  extractive  for  many  organic  substances,  and  also  for  I2, 
Br2,  O03,  FeCl3,  AuCl3,  PtCl4,  and  other  chlorides.  It  forms 
crystalline  compounds  with  various  substances,  e.g.  the  chlorides 
and  bromides  of  Sn,  Al,  P,  Sb,  and  Ti,  being  present  in  them 
as  "  ether  of  crystallization  ". 

When  dropped  upon  platinum  black  it  takes  fire,  and  when 
poured  into  chlorine  gas  an  explosion  results,  hydrochloric  acid 
being  set  free.  In  the  dark,  however,  and  in  the  cold,  sub- 
stitution by  chlorine  is  possible;  the  final  product  of  the 
substitution,  perchloro-  ether,  C4C1100,  is  solid  and  smells 
strongly  like  camphor. 

Ether  was  first  employed  as  an  anaesthetic  by  Simpson  in 
1848,  but  this  property  had  been  previously  observed  by 
Faraday.  It  is  further  used  as  an  extractive  in  the  colour 
industry,  as  Hofmann's  drops  when  mixed  with  1  to  3  volumes 
of  alcohol,  for  ice  machines,  and  for  the  preparation  of  collo- 
dion, &c. 

Methyl  ether,  (CH3)20  (Dumas,  Peligoi\  closely  resembles 
common  ether,  is  gaseous  at  the  ordinary  temperature,  but 


ISOMERISM  OF  ETHERS  87 

liquid  under  —20°,  and  is  prepared  on  the  large  scale  for 
the  production  of  artificial  cold, 

Ethyl-cetyl-  and  dicetyl  ethers  are  solid  at  the  ordinary 
temperatures. 

Several  ethers  with  unsaturated  alcohol  radicals  are  also 
known,  e.g.  allyl  ether,  (C3H5)20,  and  vinyl -ethyl  ether, 
C2H3.O.C2H5.  B.-pt.  35°-5.  These  can  combine  directly 
with  bromine. 

Isomers. — The  general  formula  of  the  saturated  ethers  is 
CnELjn+aO.  Isomerie  with  each  ether  is  a  saturated  alcohol, 
thus  C2H60  =  methyl  ether  or  ethyl  alcohol,  C4H100  =  di- 
ethyl  ether  or  butyl  alcohol.  From  C4H100  on,  however, 
several  different  isomeric  ethers  are  not  only  possible,  but  are 
also  known,  e.g.  di-ethyl  ether,  (C2H5)20,  is  isomeric  with 
methyl  -  propyl  ether,  CH3-0'C3H7;  similarly  methyl -amyl 
ether,  CH3.O.C5Hn,  ethyl-butyl  ether,  C2H5.O.C4Hg,  and 
dipropyl-ether,  C3H7»0-C3Hr,  are  all  isomeric.  Isomerism  of 
this  kind  depends  upon  the  fact  that  the  alkyl  radicals — and 
hydrogen — are  homologous,  so  that  if  the  numbers  of  carbon 
atoms  are  equal,  so  also  must  be  the  numbers  of  hydrogen. 

Such  isomerism  in  which  the  compounds  belong  to  the  same 
class  and  differ  only  in  the  nature  of  the  alkyl  group  present 
is  termed  metamerism. 

The  determination  of  the  constitution  of  the  ethers  is  based 
upon  (a)  their  syntheses  according  to  modes  of  formation  1  or  2, 
and  (b)  their  decomposition  by  HI  according  to  Keaction  4. 

Varieties  of  Isomerism. — The  cases  of  isomerism  which  have 
been  mentioned  up  to  now  are  of  three  kinds.  The  first  was 
the  isomerism  of  the  higher  paraffins,  which,  since  it  is  based 
upon  the  dissimilarity  of  the  carbon  chains,  is  often  termed 
cham-isomerism.  The  isomerism  between  ethylene  and  ethyl- 
idene  chlorides  or  between  primary  and  secondary  propyl 
alcohols  depends  upon  the  differences  in  position  of  the  substi- 
tuting halogen  or  hydroxyl  in  the  same  carbon  chain,  and  is 
termed  position  isomerism.  In  addition  to  these  there  is  the 
third  kind,  metamerism.  Further  cases  will  be  spoken  of 
under  the  Benzene  derivatives. 

B.  Thio-aleohols  and  -ethers 

The  relationship  between  oxygen  and  sulphur,  indicated  by 
their  positions  in  the  periodic  classification  of  the  elements,  is 
supported  by  a  study  of  their  carbon  derivatives.  We  have 


88  IV.   DERIVATIVES  OF  MONOHYDRIC  ALCOHOLS 

a  group  of  sulphur  compounds  analogous  to  the  monohydric 
alcohols.  These  are  known  as  thio-alcohols  or  "  thiols  ". 
Similarly  a  group  corresponding  with  the  ethers  is  known  as 
the  thio-  ethers  or  alkyl  sulphides.  These  are  liquids  of  a 
most  unpleasant  and  piercing  odour,  something  like  that  of 
leeks  ;  they  are  nearly  insoluble  in  water,  and  the  lower  mem- 
bers are  very  volatile.  The  higher  homologues  are  not  so 
soluble  in  water,  but  continue  to  be  soluble  in  alcohol  and 
ether,  and  their  smell  is  less  strong  on  account  of  the  rise  in 
the  boiling-point.  They  are  readily  inflammable. 

The  thio-alcohols,  also  called  mercaptans  or  alkyl  hydro- 
sulphides,  e.g.  mercaptan,  ethan-thiol,  Q7H5«SH,  although  of 
neutral  reaction,  possess  the  chemical  characters  of  weak  acids 
and  are  capable  of  forming  salts,  the  "  mercaptides  ",  especially 
mercury  compounds.  The  name  "  mercaptan  "  is  derived  from 
"  corpus  mercurio  aptum  ".  They  are  soluble  in  a  strong  solu- 
tion of  potash,  and  their  boiling-points  are  distinctly  lower 
than  those  of  the  corresponding  alcohols.  The  thio-ethers, 
also  termed  alkyl  sulphides,  e.g.  ethyl  sulphide,  (C2Hg)2S,  are 
on  the  other  hand  neutral  volatile  liquids  without"acid  char- 
acter. 

Both  classes  of  compounds  are  derived  from  hydrogen 
sulphide  by  the  replacement  of  either  one  or  both  atoms  of 
hydrogen  by  alkyl  groups,  just  as  alcohol  and  ether  are  derived 
from  water: 


The  boiling-points  are  methyl  mercaptan  6°,  ethyl  mercap- 
tan 36°,  methyl  sulphide  37°,  ethyl  sulphide  92°. 

The  constitution  of  these  compounds  follows  at  once  from 
their  modes  of  formation. 

Formation.  —  The  mercaptans  may  be  obtained  — 

1.  By  warming  an  alkyl  halide  or  sulphate  with  potassium 
hydrosulphide  in  concentrated  alcoholic  or  aqueous  solution  : 

C2H6Br  +  KSH  =  C2H6.SH  +  KBr. 

2.  By  heating  alcohol  with  phosphorus  pentasulphide,  the 
oxygen  being  thus  replaced  by  sulphur  (KekuU). 

The  thio-ethers  are  similarly  obtained  — 
1.  From  an  alkyl  halide  or  potassium  alkyl  sulphate  and 
normal  potassium  sulphide: 

2C2H5.S04K  + 


THIO-ETHERS  89 

2.  By  treating  ethers  with  phosphorus  pentasulphide. 
"  Mixed  sulphides  ",  comparable  with  the  "  mixed  ethers  ", 
can  also  be  prepared,.^.  methyl-ethyl  sulphide,  C2H5-S.CH3. 
Behaviour.  —  A.  The  Mercaptans. 

1.  Sodium  and  potassium  act  upon  the  mercaptans  to  form 
sodium   and   potassium   salts,    white    crystalline   compounds, 
which  are  decomposed  by  water.     The  mercury  salts  are  ob- 
tained by  warming  an  alcoholic  solution  of  mercaptan  with 
mercuric  oxide,  e.g.  mercuric  mercaptide,  Hg(C2H5S)2  (white 
plates).     With  mercuric  chloride  sparingly  soluble  double  com- 
pounds are  formed,  e.g.  (C2H5  •  S)Hg  •  Cl,  a  white  precipitate. 
The  lead  salts  are  yellow-coloured,  and  are  formed  when  alco- 
holic solutions  of  a  mercaptan  and  of  lead  acetate  are  mixed. 

2.  When  oxidized   with    nitric   acid   the  mercaptans   are 
transformed  into  alkyl-.sulph.onic  acids: 


C2H6.SH  +  30  =     fSQ  (ethyl-sulphonic  acid). 

3.  The  mercaptans  in  the  form  of  sodium  salts  are  oxidized 
by  iodine  or  by  sulphury!  chloride,  S02C12  (B.  18,  3178),  and 
also  frequently  in  ammoniacal  solution  in  the  air  to  disulphides, 
e.g.  ethyl  disulphide,  (C2H5)2S2,  thus  :  — 

2C2H6S.Na  +  I2  =  C2H6.S.S.C2H6  +  2NaI. 

These  are  disagreeably-smelling  liquids,  which  have  much 
higher  boiling-points  than  the  mercaptans.  They  are  reduced 
by  nascent  hydrogen,  and  with  nitric  acid  yield  disulphoxides, 
e.g.  ethyl  disulphoxide,  (C2H5)2S202. 

B.  The  Thio-ethers.  —  1.  They  yield  additive  compounds 
with  metallic  salts,  e.g.  (C2H5)2S,  HgCl2,  which  can  be  crystal- 
lized from  ether. 

2.  They  are  capable  of  combining  with  halogen  or  oxygen. 
Thus  ethyl  sulphide  forms  with  bromine  a  dibromide, 
(C2H5)2S  :  Br2,  crystallizing  in  yellow  octohedra,  and  with 
dilute  nitric  acid,  diethyl  sulphoxide,  (C2H5)2S:0,  a  thick 
liquid  soluble  in  water,  which  combines  further  with  nitric 
acid  to  the  compound,  (C2H5)2SO,  HN03.  Concentrated 
nitric  acid  or  potassic  permanganate  oxidizes  the  sulphides 
or  sulphoxides  to  sulphones,  e.g.  ethyl  sulphide  to  (di)-ethyl 
sulphone,  (C.,H5)2S02,  and  methyl-ethyl  sulphide  to  methyl- 
ethyl  sulphone,  (CH3)(C2H5)S02.  The  sulphones  are  solid 
well  -characterized  compounds  which  boil  without  decom- 
position. 


90  IV.   DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 

The  sulphoxides  are  reduced  by  nascent  hydrogen  to 
sulphides,  but  not  the  sulphones. 

3.  The  behaviour  of  the  sulphides  towards  the  alkyl  haloids 
is  of  especial  interest.  Thus  the  substances  (CH3)2S  and  CH3I 
combine  even  in  the  cold  to  the  white  crystalline  triinethyl- 
sulphine  iodide,  (CH8)3SI,  or  trimethyl-sulphonium  iodide,  as 
it  is  now  generally  called  in  order  to  emphasize  its  similarity 
to  the  ammonium  salts;  this  is  soluble  in  water,  and  when 
heated  is  resolved  into  its  components.  It  behaves  exactly 
like  a  salt  of  hydriodic  acid,  and  yields  with  moist  silver  oxide 
—  (but  not  with  alkali)  —  an  oily  base,  trimethyl-sulphonium 
hydroxide,  (CH3)3S-OH,  which  cannot  be  volatilized  without 
decomposition.  This  is  as  strong  a  base  as  caustic  potash, 
and  resembles  the  latter  so  closely  that  it  absorbs  carbon 
dioxide,  cauterizes  the  skin,  drives  out  ammonia,  and  gives 
salts  with  acids  even  with  hydrogen  sulphide;  these  latter 
closely  resemble  the  alkali  sulphides,  e.g.  they  dissolve  Sb2S3 
(Oefde,  1833;  Cahours). 

The  compounds  just  described  are  of  particular  interest  with 
regard  to  the  question  of  the  valency  of  sulphur. 

The  readiness  with  which  these  sulphur  compounds  are 
oxidized,  and  the  ease  with  which  they  yield  additive  com- 
pounds, is  undoubtedly  due  to  the  readiness  with  which  the 
S  atom  passes  from  the  di-  to  the  tetra-  or  hexa-valent  state; 
for  example:  — 

;;;:,,        gg>S  +  Br,  gives 
The  sulphoxides  are  — 


the  sulphones  — 

§  \ 

the  sulphonic  acids  — 


OH  /OH 

or 


and  the  sulphonium  compounds  — 

s       C2H6\g/'C2H6 


ESTERS  OF  INORGANIC  ACIDS  91 

Since  in  ethyl  sulphide  both  the  alkyl  radicals  are  bound 
to  the  sulphur,  this  will  also  be  the  case  in  ethyl  sulphone, 
otherwise  the  sulphones  would  manifestly  be  easily  saponi- 
fiable.  (See  Ethyl-hydrogen  sulphite.)  The  sulphonium  hy- 
droxides also  can  only  be  explained  very  insufficiently  as 
molecular  compounds,  on  the  assumption  of  the  divalence  of 
sulphur.  The  formula  (CH3)2S  +  CH3OH  for  trimethyl- 
sulphine  hydroxide  does  not  indicate  in  the  least  the  strongly 
basic  character  of  this  substance,  since  it  is  not  explicable  why 
the  mere  addition  of  the  neutral  methyl  alcohol  to  the  equally 
neutral  methyl  sulphide  should  produce  such  an  effect. 

With  respect  to  isomers,  the  same  general  conditions  prevail 
in  the  sulphur  as  in  the  corresponding  oxygen  compounds. 

SULPHIDES  OF  UNSATURATED  ALCOHOL  RADICALS 

Allyl  sulphide,  (C3H5)2S  (Wertlieim,  1844),  present  in  the 
oil  of  Allium  sativum — oil  of  garlic, — in  Thlasp  arvense,  &c., 
may  be  prepared  from  allyl  iodide  and  K2S  (Hofmann,  Cahours). 
B.-pt.  140°. 

Analogous  alkyl  selenium  and  tellurium  compounds  are 
also  known.  They  are  in  part  distinguished  by  their  exces- 
sively disagreeable,  nauseous,  and  persistent  odour. 

C.  Esters  of  the  Alcohols  with  Inorganic  Acids 
and  their  Isomers 

The  esters  or  alkyl  salts  may  be  considered  as  derived  from 
the  acids  (see  p.  74)  by  the  exchange  of  the  replaceable  hy- 
drogen of  the  latter  for  alkyl  radicals,  just  as  metallic  salts 
result  by  exchanging  the  hydrogen  for  a  metallic  radical: 
KN03.  (C2H6)N03. 


ethyl  chloride. 

Monobasic  acids  yield  only  one  kind  of  ester,  "neutral  or 
normal  esters",  which  are  analogous  to  the  normal  metallic 
salts  of  those  acids. 

Dibasic  acids  yield  two  series  of  esters— (1)  acid  esters  and 
(2)  neutral  esters— corresponding  respectively  with  acid  and 
normal  salts;  thus,  C2H6-HS04  and  (C2H5)2:S04  are  the  acid 


92  IV.   DERIVATIVES  OF  MONOHYDRIC  ALCOHOLS 

and  normal  ethyl  esters  of  sulphuric  acid.  Tribasic  acids  yield 
three  series  of  esters,  &c. 

The  composition  of  the  esters  or  alkyl  salts  is  therefore 
exactly  analogous  to  that  of  metallic  salts,  so  that  in  the 
definition  of  polybasic  acids  their  behaviour  in  the  formation 
of  esters  may  also  be  included. 

The  normal  esters  are  mostly  liquids  of  neutral  reaction, 
and  often  of  very  agreeable  odour,  with  relatively  low  boiling- 
points,  and  volatilize,  eventually  in  a  vacuum,  without  decom- 
position. Most  of  them  are  very  sparingly  soluble  in  water. 
The  acid  esters,  also  called  ester-acids,  on  the  other  hand,  are 
of  acid  reaction,  without  smell,  usually  very  readily  soluble 
in  water,  much  less  stable  than  the  neutral  esters,  and  not 
volatile  without  decomposition.  They  act  as  acids,  i.e.  form 
salts  and  esters. 

All  esters  are  able  to  combine  with  water,  and  are  by  this 
means  resolved  again  into  their  components,  namely,  alcohol 
and  acid,  e.g. — 

C2H5NO3  +  H2O  =  C2H6OH  +  HN03. 

This  process  occurs  when  the  ester  is  boiled  with  alkalis  or 
acids,  or  when  heated  with  steam  to  over  100°,  e.g.  150°-1SO°, 
and  is  termed  hydrolysis,  or  saponification,  when  alkalis  are 
used  (see  Soaps,  p.  158).  The  reaction  is  usually  conducted 
in  a  flask  fitted  with  a  reflux  condenser,  but  in  a  few  cases  the 
reaction  takes  place  when  the  ester  is  mixed  with  water  at  the 
ordinary  temperature. 

General  Modes  of  Formation. — 1.  The  simplest  method  for 
obtaining  an  ester  is  by  the  action  of  the  acid  on  the  alcohol, 
water  always  being  formed  as  a  by-product.  As  the  reactions 
are  reversible, 

C2H5.OH  +  O:N-OH  ^±  C2H5.0-N:0  +  H-OH, 

it  is  essential  that  the  water  formed  should  be  removed  from 
the  sphere  of  action  by  the  aid  of  concentrated  sulphuric  acid, 
fused  zinc  chloride,  &c.,  or  that  a  large  excess  of  acid  should 
be  employed,  otherwise  after  a  short  time  a  state  of  chemical 
equilibrium  is  reached,  all  four  compounds  are  present,  and 
the  direct  and  reverse  reactions  are  proceeding  at  the  same 
rate;  even  prolonged  heating  will  then  not  transform  any 
further  amounts  of  acid  and  alcohol  into  ester. 

Esters  are  therefore  often  prepared  by  adding  an  excess  of 


ESTERS  OF  NITRIC  ACID  93 

concentrated  sulphuric  acid  to  a  mixture  of  the  alcohol  and 
sodium  salt  of  the  acid. 

2.  The  alcohol  is  heated  with  the  acid  chloride,  thus : — 

-2C2H6.OH  = 

3.  The  silver  salt  of  the  acid  is  heated  with  an  alkyl  iodide; 
this  is  a  method  of  very  general  application,  although  it  often 
leads  to  isomers  of  the  expected  ester  (see  also  p.  94): 

CgHs-I  +  OiN-OAg  =  O:N-OC2H5-f  Agl. 

Besides  the  true  esters,  there  are  also  included  in  this 
division  several  other  classes  of  acid  derivatives  isomeric  with 
them,  but  distinguished  from  them  by  not  being  readily 
hydrolysed,  i.e.  by  being  more  stable,  e.g.  nitre-compounds, 
sulphonic  and  phosphinic  acids,  &c.  The  hydrocyanic  deri- 
vatives of  the  alcohols  will  also  be  described  here  for  the  sake 
of  convenience.  These,  also,  are  not  hydrolysed  in  the  normal 
manner  into  alcohol  and  acid,  but  are  decomposed  in  quite  a 
different  manner. 

ESTERS  OF  NITRIC  ACID 

Methyl  nitrate,  CH3^0«N02,  is  a  colourless  liquid,  boiling 
at  66°.  Ethyl  nitrate,  C2H5.0-N02  (Millori),  is  a  mobile 
liquid  of  agreeable  odour  and  sweet  taste,  but  with  a  bitter 
after-taste;  it  boils  at  86°,  and  burns  with  a  white  flame.  Both 
esters  are  soluble  in  water.  The  latter  is  prepared  directly 
from  the  alcohol  and  acid,  with  the  addition  of  urea  in  order 
to  destroy  any  nitrous  acid  as  fast  as  it  is  formed. 

Nitric  esters  contain  a  large  proportion  of  oxygen  in  a  form 
in  which  it  is  readily  given  up;  they  therefore  explode  when 
suddenly  heated.  They  are  very  readily  hydrolysed  to  nitric 
acid  and  the  alcohol  when  boiled  with  alkalis.  Tin  and  hydro- 
chloric acid  reduce  them  to  hydroxylamine : 

C2H5.O-N^  +  6H  =  C2H6-OH  +  H2N-OH  +  H2O. 

These  two  reactions  indicate  that  the  nitrogen  atom  is  not 
directly  united  to  carbon,  as  it  is  so  readily  removed  either  as 
nitric  acid  or  as  hydroxylamine. 


94  IV.    DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 


DERIVATIVES  OF  NITROUS  ACID 

The  compound  C2H502N  exists  in  two  isomeric  forms,  repre- 
sented by  the  formula  C2H5.0»N:0  and  C2H5-N^Q.     The 

former  is  termed  ethyl  nitrite,  as  it  is  the  true  ester  of  nitrous 
acid,  H«0«N:0;  the  isomeride  is  termed  nitro-ethane,  as  it 


contains  the  nitro  group  *N^/^  attached  to  carbon. 

a.  Alkyl  nitrites. — These  are  obtained  by  the  action  of 
nitrous  fumes  (from  arsenious  oxide  and  nitric  acid),  or  of 
potassium  nitrite  and  sulphuric  acid,  or  of  copper  and  nitric 
acid  upon  the  alcohols.  They  are  neutral  liquids  of  aromatic 
odour,  with  very  low  boiling-points,  and  are  readily  hydrolysed 
to  the  corresponding  alcohol  and  acid.  When  reduced  they 
yield  the  alcohol,  ammonia,  and  water. 

Methyl  nitrite  is  a  gas;  ethyl  nitrite  boils  at  18°,  has  a 
characteristic  odour,  and  in  the  impure  state,  as  obtained 
from  alcohol,  copper,  and  nitric  acid,  is  used  medicinally 
under  the  name  of  "sweet  spirits  of  nitre". 

Amyl  nitrite,  C5Hn-0»N:0,  is  a  pale-yellow  liquid  boiling 
at  96°,  and  is  used  in  medicine;  it  produces  expansion  of  the 
blood-vessels  and  relaxation  of  the  contractile  muscles. 

ft.  The  Nitro-derivatives  are  colourless  liquids  of  ethereal 
odour,  practically  insoluble  in  water,  and  boiling  at  tempera- 
tures some  100°  higher  than  their  isomers.  Like  the  latter 
they  distil  without  decomposition,  and  occasionally  explode 
when  quickly  heated.  They  are  fundamentally  distinguished 
from  the  alkyl  nitrites  by  not  being  readily  hydrolysed,  and 
by  yielding  aniino-compounds  (see  these)  on  reduction,  the 
nitrogen  remaining  attached  to  carbon: 

-6H  =  CH3.NH2  +  2H20. 

Nitro-methane  boils  at  99°-101°.  Nitro-ethane,  C2H5-N09 
(V.  Meyer  and  Stub&r,  1872),  boils  at  113°-114°,  burns  with  a 
bright  flame,  and  the  vapour  does  not  explode  even  at  a  high 
temperature. 

Formation.  —  1.  The  nitro -compounds  may  be  obtained  by 
treating  an  alkyl  iodide  with  solid  silver  nitrite  (V.  Meyer). 
When  methyl  iodide  is  used  nitro-methane  alone  is  formed, 
with  ethyl  iodide  about  equal  weights  of  nitro-ethane  and 
ethyl  nitrite,  and  the  higher  homologues  in  regularly  decreas- 


NITRO-DERIVATIVES  95 

ing  amounts  as  compared  with  those  of  their  isomers,  from 
which,  however,  they  may  be  readily  separated  by  distillation. 
Tertiary  alkyl  iodides  do  not  yield  mtro-coinpounds  : 


Nitromethane  is  most  readily  prepared  by  the  action  of 
sodium  nitrite  solution  on  sodium  chloroacetate,  carbon  di- 
oxide being  eliminated, 

2.  The  nitro-derivatives  of  the  lower  paraffins  cannot  be 
obtained  by  the  direct  action  of  nitric  acid  on  the  hydro- 
carbons, but  with  some  of  the  higher  derivatives  this  is  pos- 
sible, e.g.  heptane,  octane,  &c.  With  decane  a  30-per-cent 
yield  of  a  mono-nitro-derivative  may  be  obtained  by  means  of 
fuming  nitric  acid.  (W&rstall,  Am.  1898,  20,  202;  1899,  21, 
211;  Konowalo/,  Abs.  1905,  i,  764;  1907,  1,  1.)  This  method 
is  largely  employed  in  the  aromatic  series  (see  Nitrobenzene). 

The  constitution  of  the  nitro-compounds  is  based  on  the  fact 
that  they  are  not  readily  hydrolysed,  and  that  the  nitrogen  is 
not  removed  during  reduction,  but  remains  directly  bound  to 
carbon  in  the  resulting  amines  (see  these).  Consequently  the 
nitrogen  of  the  nitro-compound  is  directly  joined  to  the  alkyl 
radical  i.e.  to  carbon;  for  instance: 

/° 
CH3.N<  I,  or  more  probably  CH3-N 


.N<  I 
X) 

Nitrogen  which  is  attached  directly  to  an  alkyl  radical  is 
therefore  not  removed  by  hydrolysing  agents.  Since  the 
nitrogen  of  the  isomeric  alkyl  nitrites,  on  the  other  hand,  is 
easily  split  off  from  the  alkyl  radical  either  by  hydrolysis  or 
by  reduction,  it  is  manifestly  riot  directly  combined  with  the 
carbon  but  with  the  oxygen.  The  alkyl  nitrites,  therefore, 
receive  the  constitutional  formula  R-O-NiO,  where  R  repre- 
sents the  alkyl  radical. 

From  this  follows  for  the  hypothetical  hydrated  nitrous 
acid  the  formula  H-O-NrO,  and  for  the  anhydride  the  for- 
mula (N0)20.  The  aromatic  hydrocarbons,  e.g.  benzene,  C6Hg, 
yield  with  nitric  acid  nitro-compounds,  thus  :  — 

C6H6.H  +  HN03  =  C6H6.N02-f  H20. 

Nitric  acid,  therefore,  contains  a  nitro-  group  bound  to 
hydroxyl,  corresponding  with  the  formula  H»0»N02. 

Behaviour.  —  1.  They  yield  primary  amines  with  acid  reduc- 
ing agents,  e.g.  iron  and  acetic  acid,  tin  and  hydrochloric  acid, 


96  IV.    DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 

&c.,  substituted  hydroxylamines  being  formed  as  intermediate 
products  (V.  Meyer,  B.  1892,  25,  1714). 

2.  Primary  (.CH2-N02)  and  secondary  (:CH-N02)  nitro- 
compounds  can  yield  metallic  derivatives,  and  hence  possess 
certain   acidic  properties.      For  example,   nitro-methane  and 
mtro-ethane  react  with  alcoholic  sodium  hydroxide,  yielding 
sodium  compounds,  CH2Na.N02  and  CH3 •  CHNa •  N02.     It  is 
almost  certain  that  these  sodium  salts  are  not  true  derivatives 
of  the  nitro-compound,  but  are  derived  from  an  isomer,  the 

so-called  iso-nitro- compound   CH2:N^Vv  TT,  and  thus  sodic 

nitro-methane  has  the  constitutional  formula  CH9:NO'ONa 
(Hcllemann,  B.  1900,  33,  2913).  The  nitro-derivatives  are 
t/hus  not  true  acids,  but  pseudo  acids  (Hantzsch,  B.  1899,  32, 
1)77;  see  also  Phenylnitromethane)>  These  sodium  salts  are 
crystalline  solids,  and  are  highly  explosive. 

Tertiary  nitro-compounds  (:C-N02)  contain  no  hydrogen 
joined  to  the  carbon  atom  which  is  united  to  the  nitro-group, 
and  they  have  not  an  acid  character;  the  acidifying  influence 
of  the  nitro-group  does  not,  therefore,  extend  to  those  hydrogen 
atoms  which  are  attached  to  other  carbon  atoms. 

The  hydrogen  in  the  primary  and  secondary  nitro-deriva- 
tives, which  is  attached  to  the  same  carbon  atom  as  the  N02 
group,  can  also  be  replaced  by  bromine.  So  long  as  hydrogen, 
as  well  as  this  bromine  and  the  nitro-group,  remains  joined  to 
the  carbon  atom  in  question,  the  compound  is  of  a  strongly 
acid  character;  but  when  it  also  is  substituted  by  bromine, 
the  compound  becomes  neutral,  e.g.  dibromo-nitro- ethane, 
CH3-CBr2.N02,  is  neutral. 

The  reactivity  of  the  hydrogen  atoms  of  the  —  CH2«X02 
and  ^>CH«N02  groups,  characteristic  of  primary  and  secon- 
dary nitro-compounds,  is  exemplified  in  the  reactions  of 
these  compounds  with  aldehydes  in  the  presence  of  sodium 
carbonate.  A  primary  nitro-compound  can  combine  with 
one  or  with  two  molecules  of  formaldehyde,  yielding  com- 
pounds of  the  types  -  CH(N09)CH2 .  OH  and  -C(N02) 
(CH2.OH)2. 

3.  The  primary  nitro-compounds  yield,  with  concentrated 
hydrochloric  acid  at  140°,  acids  of  the  acetic  series  containing 
an  equal  number  of  carbon  atoms,  and  hydroxylamine. 

4.  The  reaction  of  the  nitro-compounds  with  nitrous  acid 
is  very  varied,     The  primary  yield  nitrolic  acids  and  the 


ESTERS   OF  SULPHURIC   ACID  97 

secondary  pseudo-nitrols,  while  the  tertiary  do  not  react  with 
it  at  all.  Thus  from  nitro-ethane,  CH3.orfJ^ ,  ethyl- 

TVT     f"\"llT  ^^^2 

nitrolic  acid,  CH3.C^NQ  ,  an  acid  crystallizing  in  light- 
yellow  crystals  and  yielding  intensely  red  alkali  salts,  is 
formed.  Normal  nitro-propane  acts  similarly.  Secondary 
nitro- propane,  (CH3)2 :  CH«N02,  gives,  on  the  contrary, 
propyl-pseudo-nitrol,  (CH3)2C(NO)(N02),  a  white  crystalline, 
indifferent,  non-acid  substance,  which  is  blue  either  when 
fused  or  when  in  solution.  These  reactions,  which  are  only 
given  with  compounds  of  low  molecular  weight  (in  the  primary 
up  to  C8,  and  in  the  secondary  up  to  C5),  are  specially  appli- 
cable for  distinguishing  between  the  primary,  secondary,  or 
tertiary  nature  of  an  alcohol  (see  p.  74).  The  nitre-hydro- 
carbons, which  are  readily  prepared  from  the  iodides,  are  dis- 
solved in  a  solution  of  potash  to  which  sodium  nitrite  is 
added,  the  solution  acidified  with  sulphuric  acid  and  again 
made  alkaline,  and  then  observed  for  the  production  of  a 
red  coloration  (primary  alcohol),  a  blue  coloration  (secondary 
alcohol),  or  no  coloration  (tertiary  alcohol). 

Chloropicrin,  CC13N02,  a  heavy  liquid  of  excessively  suffo- 
cating smell,  b.-pt.  112°,  is  formed  from  many  hydrocarbon 
coiri pounds  by  the  simultaneous  action  of  nitric  acid  and 
chlorine,  chloride  of  lime,  &c.  It  is  best  obtained  from  jpicric 
acid  and  bleaching-powder. 

Polynitro -derivatives  are  also  known.  Dinitromethane, 
CHo(N02).j,  an  unstable  yellow  oil;  dinitroethane,  CH3»CH 
(N02)2,  obtained  from  CH3«CHBr.N02  and  potassium  nitrite, 
b.-pt.  185°;  trinitromethane  or  nitroform,  CH(N02)3,  colour- 
less crystals,  m.-pt.  15°;  tetranitromethane,  C(N02)4,  colour- 
less crystals,  m.-pt.  13°  and  b.-pt.  126°,  is  prepared  by  the 
action  of  nitric  acid  (D  =  T53)  on  acetic  anhydride  (Chatta- 
way,  J.  C.  S.  1910,  2100).  Good  yields  (50  per  cent)  of  dinitro- 
compounds  of  the  type  N02.[CH2]n.N02  can  be  obtained  from 
the  corresponding  di-iodo-derivatives  and  silver  nitrite  (Fan 
Bmun  and  SolecU,  B.  1911,  44,  ii526)  provided  n  >  3.  The 
compounds  are  stable  and  react  with  bromine,  nitrous  acid,  &c., 
in  much  the  same  manner  as  mono-nitro-compounds.  They 
are  accompanied  by  alkylene  dinitrites,  0:N-0[CH2]n.O'N:0, 
and  nitro-nitrites,  N02-[CH2]n-O.N:0,  from  which  they  can 
be  separated  by  fractional  distillation.  The  dinitro-compounds 
can  be  used  for  the  preparation  of  dialdehydes,  since  when 

(  B  480 )  Q 


98  IV.   DERIVATIVES  OF  MONOHVDRIC  ALCOHOLS 

reduced  with  stannous  chloride  they  yield  dioximes,  and  these 
on  hydrolysis  give  dialdehydes: 

N02.[CH2]5-N02  ->  OH.N:CH.[CH2]3.CH:N.OH  -> 

1:5  Dinitro  pentane  0 :  CH  •  [CH2]3  •  CH :  O 

Glutaric  aldehyde. 

ESTERS  OF  SULPHURIC  ACID 

As  a  dibasic  acid  sulphuric  acid  can  give  rise  to  both  neutral 
or  normal  esters,  e.g.  (C2H5)2S04,  and  acid  esters  or  alkyl 
hydrogen  sulphates,  e.g.  C2H5HS04. 

The  neutral  esters  are  formed  by  the  three  general  methods : 
(a)  from  fuming  sulphuric  acid  and  alcohol;  (b)  from  silver 
sulphate  and  alkyl  iodide;  (c)  from  sulphury!  chloride  and 
alcohol : 

S02C12  +  2C2H6OH  =  S02(OC2H6)2  +  2HC1 

The  acid  esters  of  the  primary  alcohols  are  generally  pre- 
pared directly  from  their  components.  Secondary  and  tertiary 
alcohols  do  not  yield  them. 

Ethyl  sulphate,  (62115)2804,  is  a  colourless  oily  liquid  of 
an  agreeable  peppermint  odour,  insoluble  in  water,  and  solidi- 
fying on  exposure  to  a  low  temperature.  It  boils  at  208°,  is 
quickly  hydrolysed  with  boiling  water,  but  only  slowly  with 
cold  water,  yielding  alcohol  and  sulphuric  acid. 

Methyl  sulphate,  (CH3)2S04,  is  a  syrupy  oil,  b.-pt.  188°,  it 
is  extremely  poisonous,  does  not  adhere  to  glass,  and  is  a 
common  reagent  used  instead  of  methyl  iodide  for  the  forma- 
tion of  methyl  derivatives  of  phenols,  alcohols,  and  amines  (cf. 
S.  J.,  Exp.  127). 

Ethyl  hydrogen  sulphate,  C2H5O.S02-OH  (Dabit,  1802), 
is  obtained  from  a  mixture  of  alcohol  and  sulphuric  acid,  but 
not  quantitatively,  on  account  of  the  state  of  equilibrium  that 
ensues.  It  is  also  formed  from  ethylene  and  sulphuric  acid 
at  a  somewhat  higher  temperature.  It  differs  from  sulphuric 
acid  by  its  Ba-,  Ca-,  and  Pb-salts  being  soluble,  and  it  can 
therefore  be  easily  separated  from  the  former  by  means  of 
BaC03,  &c.  It  yields  salts  which  crystallize  beautifully,  e.g. 
KC2H5S04,  but  which  slowly  decompose  into  sulphate  and 
alcohol  on  boiling  their  concentrated  aqueous  solution,  espe- 
cially in  presence  of  excess  of  alkali. 

These  salts  are  frequently  used  instead  of  ethyl  iodide  for  the 
preparation  of  other  ethyl  derivatives  (process  of  ethylation). 


SULPHONIC  ACIDS   AND   DERIVATIVES  99 

The  free  acid  ester  is  prepared  by  adding  the  requisite 
amount  of  sulphuric  acid  to  the  barium  salt.  It  is  a  colourless 
oily  liquid  which  does  not  adhere  to  glass,  and  which  slowly 
hydrolyses  when  its  solution  is  evaporated  or  kept.  When 
heated  alone  it  is  decomposed  into  ethylene  and  sulphuric  acid; 
with  alcohol  it  yields  ethyl  ether  and  sulphuric  acid. 

DERIVATIVES   OF  SULPHUROUS   ACID 

a.  Alkyl  Sulphites.  —  Ethyl  sulphite,  S03(C2H5)2,  is  an 
ethereal  liquid  of  peppermint  odour,  which  can  be  prepared 
from  alcohol  and  thionyl  chloride,  SOC12,  and  which  is  rapidly 
hydrolysed  by  water.  It  has  b.-pt.  161°,  and  its  probable  con- 
stitution is:  0:S(OEt)2. 

Ethyl  Hydrogen  Sulphite.  —  The  very  unstable  potassium 
salt,  OEt-S09K,  is  formed  by  the  action  of  dry  sulphur  di- 
oxide on  potassium  ethoxide  (Rosenheim,  B.  1905,  38,  1301). 
It  is  decomposed  by  water,  yielding  alcohol  and  potassium 
sulphite. 

The  action  of  sodium  hydroxide  on  ethyl  sulphite  does  not 
hydrolyse  the  ester  to  sodium  ethyl  sulphite,  but  to  sodium 
ethyl  sulphomite,  C2H5  •  S02  •  ONa.  (B.  1898,  31,  406.) 

13.  Sulphonic  Acids.  —  Sulphonic  acids  contain  the  mono- 
valent  group  .S02-OH.  They  are  colourless  oils  or  solids, 
extremely  hygroscopic,  readily  soluble  in  water,  and  are  strong 
monobasic  acids.  They  are  much  more  stable  than  the  iso- 
meric  alkyl  hydrogen  sulphites;  for  example,  they  are  not 
hydrolysed  when  boiled  with  aqueous  alkalis  or  acids,  but  are 
decomposed  when  fused  with  potash.  They  are  non-volatile 
with  steam,  and  when  strongly  heated  decompose. 

Ethyl-sulphonic  acid,  C2H5.S02.QH  (Lowig,  1839;  H.  Kopp, 
1840),  is  a  strong  monobasic  acid,  and  yields  crystalline  salts, 
e.g.  C2H5.S03K  +  H20  (hygroscopic),  C2H5.S03Na  +  H20. 

Methyl-sulphonic  acid,  CH3.S03H,  is  a  syrupy  liquid,  and 
was  prepared  by  Kolbe  in  1845  from  trichloro-methyl-sulphonic 
chloride,  CC13.S02C1  (produced  from  CS2,  Cl,  and  H20). 

Modes  of  Formation.  —  1.  From  sodium  or  ammonium  sulphite 
and  alkyl  iodide  (or  alkyl  hydrogen  sulphate: 


Sulphonic  esters  are  formed  by  the  action  of  alkyl  iodides 
on  silver  sulphite: 

2C2H5I  +  Ag2S03  =  (C2H6)2S03  +  2AgI. 


100  IV.   DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 

2.  By  the  oxidation  of  mercaptans  by  KMn04  or  HN03: 
C2H6-SH  +  30  =  C2H5-S03H. 

The  sulphonic  acids  yield  chlorides  with  PC15,  e.g.  ethyl- 
sulphonic  acid  gives  ethyl-sulphonic  chloride,  C2H5  'SOgCl,  a 
liquid  which  boils  without  decomposition  at  177°,  fumes  in 
the  air,  and  is  reconverted  by  water  into  ethyl-sulphonic  and 
hydrochloric  acids.  Nascent  hydrogen  reduces  it  to  mercaptan, 
and  with  zinc  dust  it  yields  the  zinc  salt  of  a  syrupy,  readily 
soluble  acid,  viz.  ethyl-sulphinic  acid,  C2H5  •  S02H,  which  may 
also  be  reduced  to  mercaptan.  Sodium  ethyl  sulphinate  yields 
ethyl  sulphone  when  treated  with  ethyl  bromide,  C2H5Br. 
When  esterified  the  acid  forms  an  unstable  ester,  isomeric  with 
ethyl  sulphone  (B.  24,  2272). 

Ethyl  Ethyl-sulphonate,  C2H5-S02'OC2H5,  is  isomeric  with 
ethyl  sulphite,  and,  being  an  ester  of  the  more  stable  ethyl- 
sulphonic  acid,  can  only  be  partially  hydrolysed.  It  is  pre- 
pared from  silver  sulphite  and  ethyl  iodide.  It  boils  at  213°, 
and  the  sulphonic  esters  generally  have  considerably  higher 
boiling-points  than  the  isomeric  alkyl  sulphites. 

Constitution. — From  the  formation  of  the  sulphonic  acids 
from  mercaptans  by  oxidation,  and  the  (indirect)  reversibility 
of  this  reaction,  it  follows  that  the  sulphur  in  them  is  directly 
attached  to  the  alkyl  radical;  if,  then,  sulphur  is  regarded  as 
hexavalent,  ethyl-sulphonic  acid  has  the  constitution 

C2H6.S02-OH  = 

This  constitution  is  in  perfect  harmony  with  the  reaction  of 
the  acids  with  phosphorus  pentachloride  and  also  with  their 
monobasicity.  From  this  we  might  conclude,  assuming  that 
the  conversion  of  metallic  sulphites  into  sulphonic  acid  deriva- 
tives is  a  simple  exchange  of  alkyl  and  metallic  radicals,  that 
the  constitution  of  sodium  sulphite  is  Na-S02«ONa,  of  the 
hypothetical  sulphurous  acid  H«S02»OH,  and  of  sulphuric 
acid  OH-S02«OH.  The  alkyl  sulphites  formed  from  thionyl 
chloride  probably  have  the  alkyl  groups  attached  to  oxygen, 
e.g.  ethyl  sulphite,  SO(OC2H6)2. 

Esters  of  phosphoric  acid  PO(OK)3,  PO(OE)2(OH),  and 
PO(OR)(OH)2,  (K  =  alkyl),  exist,  as  do  also  similar  com- 
pounds of  phosphorous  and  hypophosphorous  acids.  The 
phosphinic  acids,  &c.,  are  related  to  the  two  last-mentioned 
classes.  Esters  of  boric  and  silicic  acids  are  also  known. 


REACTIONS   OF  NITRIDES;  ;  >>"h "  ^^1 

ALKYL  DERIVATIVES  OF  HYDROCYANIC  ACID 

Hydrocyanic  acid,  HCN,  yields  two  classes  of  derivatives 
by  the  exchange  of  its  hydrogen  atom  for  alkyl  radicals, 
neither  of  which  can  be  regarded  as  esters,  in  the  sense  that 
they  are  hydrolysed  to  the  acid  and  alcohol. 

a.  Alkyl  Cyanides  or  Nitriles,  E-C-N. — These  are  either 
colourless  liquids,  which  volatilize  without  decomposition,  or 
solids,  with  an  ethereal  odour  slightly  resembling  that  of 
leeks;  they  are  lighter  than  water,  and  are  relatively  stable. 
The  lower  members  are  miscible,  with  water,  but  the  higher 
ones  not,  and  they  boil  at  about  the  same  temperatures  as  the 
corresponding  alcohols. 

Formation. — 1.  By  heating  an  alkyl  iodide  with  an  alcoholic 
solution  of  potassium  cyanide,  or  potassium  ethyl -sulphate 
with  potassium  ferrocyanide : 

CH3I  +  KCN  =  Kl-f  CH3.  ON  (methyl  cyanide). 

2.  From  fatty  acids,   e.g.  acetic  acid,  CH3-CO.OH.      The 
ammonium  salt  when  distilled  loses  water  and  yields  the  acid 
amide,  e.g. : 

CH3.CO-ONH4  =  H2O  +  CH3.CO-NH2(acetamide). 

The  amide  when  heated  with  a  dehydrating  agent,  e.g.  P4010, 
loses  a  second  molecule  of  water  and  yields  the  cyanide : 
CH3-CO.NH2  =  H2O  +  CH3-C:N. 

As  a  consequence  of  this  mode  of  formation  these  com- 
pounds are  also  termed  nitriles  of  the  monobasic  acids,  e.g. 
CHg-CN,  methyl  cyanide  or  aceto-nitrile ;  C2H5-CN,  propio- 
nitrile,  &c. 

3.  The  higher  nitriles,  in  which  C>5,  are  formed  from  the 
amides  of  acids  of  the  acetic  series  containing  1  atom  of  carbon 
more  in  the  molecule,  and  also  from  the  primary  amines  with 
the  same  number  of  carbon  atoms,  upon  treatment^with  bro- 
mine and  caustic-soda  solution  (Hofmann).     See  Amides. 

4.  From  the  oximes  of  the  aldehydes,  by  warming  with 
acetic  anhydride.     See  Aldoximes. 

Reactions.—  The  nitriles  are  chemically  active.  Most  of  the 
reactions  are  of  an  additive  nature,  and  are  somewhat  similar 
to  those  characteristic  of  the  olefines.  These  reactions  are  in 
harmony  with  the  constitutional  formulae  usually  attributed 
to  the  nitriles,  e.g.  R.C|N,  according  to  which  a  triple  bond 
exists  between  a  nitrogen  and  a  carbon  atom. 


102      .  'f.V.ERrtfATIYES   OF  "MONOHYDRIC  ALCOHOLS 


1.  When  hydrolysed  with  acids  or  alkalis,  or  superheated 
with  water,  they  take  up  water  (2  mols.)  and  yield  the 
ammonium  salts  of  fatty  acids  (with  alkalis,  the  alkali  salt, 
and  free  ammonia).  The  reaction  undoubtedly  proceeds  in 
two  distinct  stages,  and  an  acid  amide  is  first  formed: 


CH3.CO-NH2-fH20  =  CH3.CO.ONH4. 

It  is  generally  impossible  to  stop  the  hydrolysis  at  the  first 
stage  in  the  case  of  aliphatic  nitriles,  but  this  is  readily 
accomplished  with  aromatic  cyanides.  This  is  a  reaction  of 
considerable  interest,  as  it  enables  us  to  pass  from  a  saturated 
alcohol,  CnH2n+1-OH,  to  the  aliphatic  acid,  CnHta+1  •  COOH, 
which  contains  1  atom  of  carbon  more  than  the  alcohol: 

CH3.OH  ->  CH3I  -»  CH3.CN  —  CH3.COOH. 

2.  Just  as  acetamide  is  formed  by  the  taking  up  of  water, 
so  is  thio-acetamide  by  the  addition  of  sulphuretted  hydrogen, 

3.  By  the  addition  of  hydrochloric  acid,  amido-chlorides  or 
imido-chlorides  are  formed  ;  by  the  addition  of  ammonia  bases, 
amidines.    Halogens  also  form  decomposable  additive-products. 

4.  Primary  amines  are  obtained  by  the  reduction  of  nitriles 
with  sodium  and  alcohol  (p.  106): 

CH3.C!N  +  4H  =  CH3.CH2.NH2(ethylaimne). 

5.  Metallic  potassium  or  sodium  frequently  induces  poly- 
merization;  thus  methyl  cyanide  yields  in  this  way  cyan- 
methine,  a  mono-acid  base  crj^stallizing  in  prisms. 

Aceto-nitrile,  Ethane-nitrile,  CH3»CN,  b.-pt.  82°  is  present  in 
the  products  of  distillation  from  the  vinasse  of  sugar  beet  and 
in  coal-tar.  Propio-nitrile;  (Propane-nitrile),  C2H5'CN,  butyro- 
nitrile,  C3H7'CN,  and  valero-nitrile,  C4H9»CN,  are  liquids  of 
-agreeable  bitter-almond-oil  odour;  palmito-nitrile,  C15H31»CN, 
is  like  paraffin. 

P.  Isocyanides,  Isonitriles  or  Carbylamines.  —  These  are 
colourless  liquids  readily  soluble  in  alcohol  and  ether,  but 
only  slightly  soluble  in  water.  They  have  a  feeble  alkaline 
reaction,  an  unbearable  putrid  odour,  and  poisonous  proper- 
ties, and  boil  somewhat  lower  than  the  isomeric  nitriles. 

Formation.  —  1.  By  heating  an  alkyl  iodide  with  silver 
cyanide  instead  of  potassium  cyanide  (Gautier),  a  double  com- 


CONSTITUTION   OF  CYANIDES  AND  ISOCYANIDES         103 

pound  with  silver  cyanide  being  first  formed,  according  to 
Wade  : 

Ag-N:C:  +  EtI  =    EtANzC:  =  AgI  +  Et-N:C: 

I'  (ethyl  carbylamine). 

2.  In  small  quantity,  along  with  the  nitrile,  when  a  potassium 
alkyl-sulphate  is  distilled  with  potassium  cyanide. 

3.  By  the  action  of  chloroform  and  alcoholic  potash  upon 
primary  amines  (Hofmann,  1869)  (see  pp.  63  and  108): 

CH3.NH2  +  CHC13  +  3KOH  =  CH3.N:C  +  3KC1  +  3H2O. 

Behaviour.  —  1  .  The  isonitriles  differ  fundamentally  from  the 
nitriles  in  their  behaviour  with  water  or  dilute  acids.  When 
strongly  heated  with  water,  or  with  acids  in  the  cold,  they 
decompose  into  formic  acid  and  a  primary  amine  containing 
an  atom  of  carbon  less  than  themselves: 


Unlike  the  nitriles,  they  are  very  stable  towards  alkalis. 

2.  The  isonitriles  are  also  capable  of  forming  additive  pro- 
ducts with  the  halogens,  HC1,  H2S,  &c.,  compounds  different 
from  those  given  by  the  nitriles;  thus,  with  HC1  they  yield 
crystalline  salts  which  are  rapidly  decomposed  by  water  into 
amine  and  formic  acid. 

3.  Some  of  the  isonitriles  change  into  the  isomeric  nitriles 
when  heated.     According  to  Wade  this  change  does  not  occur 
at   all   readily  in   the   fatty  series   if  the   carbylamines  are 
thoroughly  dry.     (J.  C.  S.  1902,  81,  1596.) 

Methyl  isocyanide,  CH3-NC,  boils  at  58°,  and  ethyl  iso- 
cyanide,  C2H5«NC,  at  82°. 

Constitution  of  the  Nitriles  and  Isonitriles.  —  The  constitution 
of  the  nitriles  follows  from  the  readiness  with  which  they  can 
be  hydrolysed  to  acids  of  the  acetic  series.  In  acetic  acid 
we  know  that  we  have  a  methyl  group  directly  attached  to 
a  carbon  atom,  e.g.  CH3  •  CO  •  OH,  and  since  methyl  cyanide 
on  hydrolysis  yields  acetic  acid,  it  also  presumably  contains 
the  methyl  group  attached  to  carbon.  The  nitrogen  atom, 
on  the  other  hand,  is  eliminated,  and  is  thus  probably  not 
directly  bound  to  the  alkyl  radical.  Consequently  aceto-nitrile 
has  the  constitution  CH3»C:N. 

This  constitutional  formula  is  supported  by  a  study  of  the 
product  formed  on  reduction,  namely  CH3»CH2«NH2. 


104  IV.    DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 

In  the  case  of  the  isonitriles,  however,  it  is  the  nitrogen 
which  must  be  directly  bound  to  the  alkyl  radical,  as  their 
close  connection  with  the  amine  bases  shows,  the  amines  being 
easily  prepared  from  and  reconverted  into  the  isonitriles. 
The  carbon  atom  of  the  cyanogen  group,  on  the  contrary,  is 
eliminated  as  formic  acid  on  decomposition  with  acid,  and  is 
consequently  not  directly  united  to  the  alkyl  radical,  but  only 
through  the  nitrogen.  The  constitutional  formula  of  methyl 
isocyanide  is  therefore  either  CH3«N:C  or  CH3-N:C:,  with 
an  unsaturated  carbon  atom  (cf.  Chap.  LII). 


D.  Amines  or  Nitrogen  Bases  of  the  Alkyl  Radicals 

By  the  introduction  of  alkyl  radicals  in  place  of  hydrogen 
into  the  ammonia  molecule,  the  important  class  of  ammonia 
bases  or  amines  is  formed. 

The  amines  containing  small  alkyl  groups  bear  the  closest 
resemblance  to  ammonia,  and  are  even  more  strongly  basic 
than  the  latter.  They  have  an  ammoniacal  odour,  give 
rise  to  white  clouds  with  volatile  acids,  combine  with  hydro- 
chloric acid,  &c,,  to  salts  with  evolution  of  heat,  and  yield 
platini-  and  auri-chlorides.  Their  aqueous  solutions  precipitate 
insoluble  hydroxides  from  solutions  of  the  salts  of  the  heavy 
metals,  and  these  precipitates  are  frequently  soluble  in  excess. 

The  lowest  members  of  this  class  are  combustible  gases 
readily  soluble  in  water.  The  next  are  liquids  of  low  boiling- 
point,  also  at  first  readily  soluble;  but  the  solubility  in  water, 
and  also  the  volatility,  decrease  with  an  increase  in  molecular 
weight,  until  the  highest  members  of  the  series,  such  as  tricetyl- 
amine,  (C16H33)3N,  are  at  the  ordinary  temperature  odourless 
solids  of  high  boiling-point,  insoluble  in  water  but  soluble  in 
alcohol  and  ether,  and  readily  combining  with  acids  to  form 
salts.  All  amines  are  considerably  lighter  than  water. 

The  quaternary  ammonium  hydroxides  are  solid  and  very 
hygroscopic,  and  exceedingly  like  potash  in  properties. 

Classification. — The  bases  are  divided  into  primary,  secondary, 
tertiary,  and  quaternary  bases,  according  as  they  contain  1,  2, 
3,  or  4  alkyl  radicals;  the  three  first  are  derived  from  am- 
monia, and  the  last  from  the  hypothetical  ammonium  hy- 
droxide, NH4.OH.  Characteristic  of  primary  amines  is  the 
amino  group,  'NHg,  of  secondary,  the  imino  group,  :NH,  and 
of  tertiary,  the  N  radical  attached  to  three  alkyl  groups. 


FORMATION   OF  AMINES  105 

The  system  of  nomenclature  is  simple,  as  indicated  by  the 
following  examples:  —  CH3»NH2,  methylamine  ;  C3H7'NH2, 
propylamine;  (C2H5)2NH,  di-ethylamine;  (CH3)3N,  trimethyl- 
amine;  and  N(C2H5)4I,  tetraethylammonium  iodide. 

The  alkyl  radicals  may  be  either  saturated  or  unsaturated. 

Modes  of  Formation.  —  1.  Primary  amines,  e.g.  methylamine, 
ethylamine,  are  obtained  by  heating  alkyl  cyanates  with 
potash  solution  (Wurtz,  1848),  just  as  cyanic  acid  itself  yields 
ammonia  and  carbon  dioxide  : 


2.  By  the  direct'  introduction  of  the  alkyl  radical  into 
ammonia  by  heating  a  concentrated  solution  of  the  latter  with 
methyl  iodide,  chloride,  or  nitrate,  ethyl  iodide,  &c.  In  this 
reaction  an  atom  of  hydrogen  is  first  exchanged  for  an  alkyl 
radical,  and  then  the  base  produced  combines  with  the  halogen 
hydride,  formed  at  the  same  time,  to  a  salt,  thus  :  — 

(I)  NH2H  +  CH3I  =  NH2.CH3,  HI. 

From  the  methylamine  hydriodide  thus  produced,  free 
methylamine  can  readily  be  obtained  by  distillation  with 
potash  : 

NH2(CH3),  HI  +  KOH  =  NH2(CH3)  +  KI  +  H2O. 

The  methylamine  can  now  combine  further  with  methyl 
iodide  to  hydriodide  of  dimethylamine  : 

(II)  NH2(CH3)  +  CH3I  =  NH(CH3)2HI, 

tthich,  in  its  turn,  yields  the  free  base  with  potash.  This 
latter  can  again  combine  with  methyl  iodide: 

(III)  NH(CH3)2  +  CH3I  =  N(CH3)3HI, 

the  salt  so  produced  yielding  trimethylamine  as  before. 
Finally,  the  trimethylamine  can  once  more  take  up  methyl 
iodide  : 

(IV)  N(CH3)3  +  CH3I  =  N(CH3)4I. 

The  compound  obtained,  tetramethylammonium  iodide,^  is, 
however,  no  longer  a  salt  of  an  amine,  but  of  an  ammonium 
base,  and  is  not  decomposed  on  distillation  with  potash  solu- 
tion. The  velocities  of  formation  of  quaternary  ammonium 
iodides  from  tertiary  amines  and  alkyl  iodides  have  been 
determiner!  bv  Menwhutkin.  The  reaction  has  been  shown 


106         IV.   DEBIVATIVES  OP  MONOHYDRIO  ALCOHOLS 

to  be  a  bimolecular  one.  The  velocity  varies  with  the  alkyl 
iodide  employed,  decreasing  as  the  alkyl  group  becomes  more 
complex.  The  solvent  employed,  for  example,  acetone,  hexane, 
methyl  alcohol,  &c.,  also  affects  the  velocity  of  formation  to 
an  enormous  extent,  e.g.  the  combination  of  ethyl  iodide  and 
try-ethylamine  takes  place  some  250  times  as  readily  in  ethyl 
alcohol  as  in  hexane  solution. 

Primary  and  secondary  bases  can  also  be  transformed  into 
secondary  and  tertiary  by  warming  with  potassium  alkyl- 
sulphates  (B.  1891,  24,  1678). 

When,  several  alkyl  iodides  are  used  in  place  of  methyl 
iodide,  mixed  amines,  i.e.  amines  containing  different  alkyl 

ups  in  the  molecule,  are  obtained,  e.g.  methyl-propylamine, 

H(CH3)(C3H7),  methyl-ethyl-propy'lamine,  N(CH3)(C2H5) 
(C3Hr). 

The  reactions  I  to  IV  given  above  do  not  in  reality  follow 
each  other  in  perfect  order  but  go  on  simultaneously,  the  bases 
being  partly  liberated  from  the  hydriodides  by  the  ammonia, 
and  so  being  free  to  react  with  more  alkyl  haloid.  The  pro- 
duct obtained  by  distillation  with  potash  is  therefore  a  mixture 
of  all  the  three  amines  and  ammonia. 

These  cannot  be  separated  by  fractional  distillation,  and  so 
their  different  behaviour  with  ethyl  oxalate,  OEt-CO-CO-OEt, 
is  made  use  of  for  the  purpose.  Methyl amine  reacts  with  this 
ester  to  form  chiefly  (1)  dimethyl-oxamide,  CH3NH.  CO -CO- 
NK •  CH3  (solid),  and  (2)  some  methyl-oxamie  ester,  OEt  •  CO  • 
CO-NH-CH3  (liquid);  dimethylamine  yields  (3)  the  ethyl  ester 
of  dimethyl-oxamic  acid,  OEt-CO-CO-N(CH3)2  (liquid),  while 
trimethylamine  does  not  react  with  the  ethyl  oxalate.  Upon 
warming  the  product  of  the  reaction  on  the  water-bath,  the 
latter  base  distils  over,  and  the  remaining  compounds  can 
then  be  separated  by  special  methods  (for  which  see  B.  3,  776; 
8,  760),  and  individually  decomposed  by  potash,  (1)  and  (2) 
yielding  methylamine,  and  (3)  dimethylamine. 

3.  The  nitro-compounds  yield  primary  amines  when  treated 
with  acid  reducing  agents  (see  p.  95),  thus : — 

CH3.N02-f  6H  =  CH3.NH2  +  2H20. 

4.  The  nitriles,  including  hydrocyanic  acid,  are  capable  of 
taking  up  four  atoms  of  hydrogen  (see  p.  102)  and  forming 
primary  amines  (Menditis,  1862): 

CH3.C:N  +  4H  =  CH3-CH2.NH2  (ethylamine). 


PROPERTIES   OF  AMINES  107 

5.  Primary  amines,  in  which  C  <  6,  are  prepared  according 
to  Hofmann's  method,  by  the  action  of  bromine  and  caustic- 
soda  solution  upon  the  amides  of  acids  containing  1  carbon 
atom  more  than  themselves  (see  Amides). 

6.  Primary  amines  likewise  result  from  the  reduction  of 
the  oximes  or  hydrazones  (see  pp.  127  and  135):  for  example, 
acetaldoxime : 

CH3.CH:N.OH-]-4H  =  CH3.CH2.NH2  +  H2O. 

7.  See  p.  463  for  preparation  of  amines  from  phthalimide. 
Isomers. — Numerous  isomers  exist  among  the  amines,  as  the 

following  table  shows : — 


C2H7N. 

C3H9N. 

C4HnN. 

Isomers 

NH2(C2H5) 
NH(CH3)2 

NH2(C3H7) 
NH(CH3)(C2H6) 
N(CH3)3 

NHo(C4H9) 
NH(CHS)(C8HT)  and  NH(C2H5)2 
N(CH3)2(C2H6) 

This  kind  of  isomerism  is  the  same  as  that  of  the  ethers 
(p.  87),  i.e.  metamerism.  From  (C3Hr)  onwards,  isomerism  can 
also  occur  in  the  alkyl  radicals.  According  to  theory,  as  many 
amines  Cn  as  alcohols  Cn+1  are  capable  of  existence. 

Behaviour.  —  1.  The  amines  combine  directly  with  acids  (or- 
ganic or  inorganic)  to  form  salts  in  exactly  the  same  way  as 
ammonia;  the  quaternary  ammonium  bases,  however,  react 
with  acids,  forming  salts  and  eliminating  water  like  potassium 
or  ammonium  hydroxide  : 


CH3.NH2  +  HC1  =  CH3.NH2,  HC1  =  CH3.NH3CL 
(CH3)4N.OH  +  HC1  =  (CH3)4N.C1  +  H2O. 

The  salts  so  obtained  are  white,  crystalline  compounds, 
readily  soluble  in  water,  and  frequently  hygroscopic.  The 
chlorides  form,  with  platinic  chloride,  sparingly  soluble  platini- 
chlorides  analogous  to  ammonium  platinichloride,  (NH4)2PtCl6, 
e.g.  methylamine  platinichloride,  (CH3NH3)2PtCl6. 

The  same  applies  to  the  aurichlorides,  e.g.  C2H5NH3AuCl4. 

Strong  alkalis,  e.g.  potassium  hydroxide,  decompose  all  the 
salts  with  the  exception  of  the  quaternary  ammonium  com- 
pounds yielding  the  free  bases  (and  not  ammonia). 

2.  Hydrolysing  agents  such  as  alkalis  and   acids  do  not 
affect  the  nitrogen  bases  of  the  alcohol  radicals. 

3.  The  different  classes  of  amines  are  distinguished  from 


108  IV.   DERIVATIVES  OF  MONOHYDRIC  ALCOHOLS 

each  other  by  the  primary  having  2  hydrogen  atoms,  the 
secondary  1,  but  the  tertiary  none  replaceable  by  alkyl 
groups;  the  same  applies  to  acid  radicals  (acyl  groups).  The 
ultimate  products  obtained  from  isomeric  amines  by  the  action 
of  methyl  iodide  are  distinguished  from  one  another  by  ana- 
lysis. Thus  of  the  three  isomeric  amines  C3H9N,  propylamine 
gives  with  methyl  iodide,  C8H7.«N(CH3)3I,  propyl-trimethyl- 
ammonium  iodide  =  C6H16NI;  methyl-ethylamine  gives  C2H5» 
N(CH3)3I,  ethyl-trimethylammonium  iodide  =  C5H14NI;  and 
trimethylamine  gives  N(CH3)4I,  tetramethylammonium  iodide 
=  C4H12NI.  An  iodine  estimation  in  the  final  product  would 
immediately  enable  us  to  settle  the  constitution  of  the  original 
amine. 

The  primary  bases  further  differ  from  the  others  in  their 
behaviour  with  chloroform,  carbon  disulphide,  and  nitrous  acid. 

4.  Only  the  primary  bases  react  with  chloroform  and  alco- 
holic potash,  with  formation  of  isonitriles  (p.  103). 

5.  When  warmed  with  carbon  disulphide  in  alcoholic  solu- 
tion, the  primary  and  secondary,  but  not  the  tertiary,  bases 
react  to  form  derivatives  of  thiocarbamic  acids.     (See  Carbonic 
Acid  Derivatives.)     Should  the  amines  be  primary  ones,  the 
characteristically  smelling  isothiocyanates  are  produced  upon 
heating  the  thiocarbamic  derivatives  with  a  solution  of  HgCl9 
("  Senfol  "  reaction). 

6.  Nitrous  acid  reacts  with  the  primary  amines,  forming 
alcohols,  e.g.  — 


A  molecular  rearrangement  is  occasionally  met  with,  e.g. 
the  production  of  isopropyl  alcohol  from  ?i-propylamine. 

Secondary  bases  yield  with  nitrous  acid  nitroso-compounds, 
e.g.  "  diinethyl-nitrosamine  "  : 

(CH3)2NH  +  NO.OH  =  (CH3)2N.NO  +  H20. 

These  nitrosamines  are  yellow-coloured  volatile  liquids  of 
aromatic  odour  (Geuther).  When  reduced  with  acid-reducing 
agents,  or  when  heated  with  alcohol  and  hydrochloric  acid, 
they  regenerate  the  secondary  amines.  Weak  reducing  agents, 
however,  convert  them  into  hydrazines  (p.  112).  The  nitros- 
amines are  frequently  of  great  service  in  the  purification  of 
the  secondary  bases. 

Nitrous  acid  has  no  action  upon  tertiary  amines. 

7.  By  the  indirect  action  of  nitric  acid  (B.  22,  Ref.  295), 


PROPERTIES   OF  AMINES  109 

nitr  amines  result,  i.e.  amines  in  which  an  amino-hydrogen  atom 
has  been  replaced  by  the  nitro-  group,  e.g.  CH3.NH.N02, 
methyl-nitramine.  Similarly,  by  the  indirect  introduction  of 
an  amino-group,  hydrazines  are  formed,  e.g.  CH3«NH»NH2, 
methyl-hydrazine. 

8.  While  the  amines  are  liberated  from  their  salts  by  alkalis, 
the  free  bases  of  the  quaternary  ammonium  salts,  e.g.  tetra- 
methylammonium  iodide,  cannot  be  prepared  from  these  by 
treatment  with  potash,  because  the  products  are  soluble  and 
non-gaseous,  and  hence  an  equilibrium  is  attained.  The  salts 
behave  normally  in  aqueous  solutions,  for  example,  the  iodides 
yield  precipitates  with  silver  nitrate,  and  are  good  electrolytes, 
The  corresponding  hydroxides,  e.g.  N(CH3)4OH,  are  obtained 
most  readily  by  acting  upon  the  iodides  with  moist  silver 
oxide.  These  hydroxides  are  extraordinarily  like  caustic 
potash.  They  are  colourless  hygroscopic  solids,  readily  soluble 
in  water,  and  abstract  carbon  dioxide  from  the  air.  The  solu- 
tions have  strongly  alkaline  properties,  are  good  electrolytes, 
and  precipitate  metallic  hydroxides  from  solutions  of  their 
salts.  When  distilled  they  decompose,  yielding  the  tertiary 
base,  the  tetramethyl  base  yielding  in  addition  methyl  alcohol, 
and  the  homologous  bases  olefine  and  water  (Braun,  A.  382,  1): 

N(CH,),.OH    =  N(CH3)3  +CH3.OH. 
N(C2H6)4.OH  = 


They  are  of  importance  for  the  study  of  the  valency  of 
nitrogen.  Their  formation  and  general  properties  are  most 
in  harmony  with  the  assumption  of  a  penta-  or  quinque-valent 

PTT          /       3 
nitrogen  atom,  e.g.  ™3/>N-CH3,  and  not  as  a  so-called  mole- 


cular  compound,  N(CH3)3,  CH3I.  (Cf.  Trimethyl-sulphonium 
hydroxide.)  The  fact  that  the  salts  N(CH8)»(C2H6)  +  C^Cl 
and  N(CH3)(C2H5)2  +  CH3C1  are  identical,  is  in  agreement  with 
the  former  assumption.  (Meyer  and  Lecco.)  Lastly,  optically 
active  isomers  are  met  with  among  the  quaternary  ammonium 
salts,  a  point  which  receives  its  readiest  explanation  from  the 
asymmetry  of  the  molecule  containing  a  quinquevalent  nitrogen 
atom.  (See  Stereochemistry  of  Nitrogen  Derivatives.) 

9.  The  quaternary  iodides  are  resolved  into  tertiary  base 
and  alkyl  iodide  when  heated.  They  combine  with  2  or  4 
atoms  of  bromine  or  iodine  to  tri-  and  penta-bromides  or 
-iodides,  e.g.  N(CH3)4.U4  (dark  needles),  and  N(C2H5)4M2 


110 


IV.   DERIVATIVES  OF  MONOHYDRIC  ALCOHOLS 


(azure-blue  needles).  Such  periodides  readily  lose  the  excess 
of  iodine,  and  are  hence  relatively  unstable.  Hepta-  and  Ennea- 
iodides  also  exist. 

The  following  table  gives  the  boiling-points  of  the  various 


amines:- 


Primary. 

Secondary. 

Tertiary. 

Methyl  .  . 

—  6° 

7° 

3'5° 

Ethyl  

19° 

56° 

90° 

ft-Propyl  

49° 

98° 

156° 

w-Butyl     .  . 

76° 

160° 

215° 

7i-0ctyl  

180° 

297° 

366° 

Methylamine,  CH3  •  NH2,  occurs  in  Mercurialis  perennis 
and  annua  ("  mercurialin "),  in  the  distillate  from  bones  and 
wood,  and  in  herring  brine.  It  is  produced  in  many  decom- 
positions of  organic  compounds,  e.g.  from  alkaloids,  as  when 
caffeine  is  boiled  with  barium  hydroxide;  also  by  heating 
trimethylamine  hydrochloride  to  285°. 

It  is  most  readily  prepared  from  acetamide,  caustic  soda,  and 
bromine.  (B.  18,  2737.)  It  is  more  strongly  basic  and  even 
more  soluble  in  water  than  ammonia,  has  a  powerful  ammo- 
niacal  and  at  the  same  time  fishlike  odour,  and  burns  with  a 
yellowish  flame.  Its  aqueous  solution,  like  that  of  ammonia, 
precipitates  many  metallic  salts,  frequently  redissolving  the 
precipitated  hydroxides;  unlike  ammonia,  it  does  not  dissolve 
Ni(OH)2  and  Co(OH),. 

The  hydrochloride,  CH3»NH2,  HC1,  forms  large  glistening 
plates,  is  very  hygroscopic  and  readily  soluble  in  alcohol;  the 
platinichloride  crystallizes  in  golden  scales,  and  the  sulphate 
forms  an  alum. 

Dimethylamine,  (CH3)2NH,  occurs  in  Peruvian  guano  and 
pyroligneous  acid,  and  is  formed  by  decomposing  nitroso-di- 
methyl-aniline  by  caustic-soda  solution. 

Trimethylamine,  (CH3)3N,  is  widely  distributed  in  nature, 
being  found  in  considerable  quantity  in  Chenopodium  vulvariu, 
also  in  Arnica  montana,  in  the  blossom  of  Cratcegus  oxyacantlw, 
and  of  pear,  and  in  herring  brine.  (Werthdm.) 

It  is  a  decomposition  product  of  the  betaine  of  beet-root, 
and  therefore  along  with  ammonia,  dimethylamine,  &c., 
methyl  alcohol  and  aceto  -  nitrile  •  by  the  distillation  of 


II YDBOXYL  AMINES  AND   HYI'BAZISES  111 

vinasse.     It  has  an  ammoniacal  and  pungent  fishlike  odour. 

The  tertiary  amines  can  be  oxidized  by  means  of  hydrogen 
peroxide  to  compounds  of  the  type  (CH3)3N  :  0,  trimethyl- 
amine  oxide,  whijh  are  colourless  crystalline  bases. 

Tetramethylammonium  iodide,  N(CHS)4I,  is  obtained  in 
large  quantity  directly  from  IS[H3  +  CH3I.  It  crystallizes  in 
white  needles  or  large  prisms,  and  has  a  bitter  taste. 

Tetramethylammonium  hydroxide,  N(CH3)4OH,  crystallizes 
in  hygroscopic  needles,  and  can  be  obtained  by  the  action  of 
alcoholic  potash  on  an  alcoholic  solution  of  its  chloride;  potas- 
sium chloride  is  precipitated,  and  the  hydroxide  remains  in 
solution.  It  forms  salts,  e.g.  a  platinichloride,  sulphide,  poly-' 
sulphide,  cyanide,  &c. 

Ethylamine,  C2H6NH2.  Crude  ethyl  chloride  (obtained  as 
a  by-product  in  the  manufacture  of  choral)  is  used  for  its  pre- 
paration. It  has  a  strongly  ammoniacal  smell  and  biting  taste, 
mixes  with  water  in  every  proportion,  and  burns  with  a  yellow 
flame.  It  dissolves  A1(OH)3,  but  not  Fe(OH)3;  also  Cu(OH)2 
with  difficulty,  but  not  Cd(OH)2.  With  bleaching  powder  it 
yields  ethyl-dichloro-amme,  C2H5'NC12,  as  a  yellow  oil  of  a 
most  unpleasant  piercing  odour. 

Tri-ethylamine,  (C2H5)3N,  is  an  oily  strongly  alkaline  liquid. 
The  precipitates  which  it  gives  with  solutions  of  metallic  salts 
are  mostly  insoluble  in  excess  of  the  precipitant. 

HYDROXYLAMINES ;   HYDRAZINES 

The  Alkyl-hydroxylamines,  which  are  derived  from  hy- 
droxylamine,  NH2»OH,  just  as  the  amines  are  from  ammonia, 
belong  to  two  different  series,  in  accordance  with  the  constitu- 
tion of  hydroxylamine,  thus : — 

NH2.OCH3        and        CHg-NH-OH 

a-Methyl-hydroxylamine  /3-Methyl-hydroxylamine. 

The  compounds  of  the  first  series,  which  are  obtained  from 
the  oxime  ethers  (p.  138),  are — as  ethereal  compounds — toler- 
ably stable,  and  do  not  reduce  Fehling's  solution.  Those  of 
the  second  series,  which  likewise  result  from  certain  pxime 
derivatives,  but  at  the  same  time  also  from  the  reduction  of 
the  nitro-hydrocarbons  (p.  96),  very  readily  undergo  change, 
reduce  Fehling's  solution  even  in  the  cold,  and  yield  primary 
amines  when  further  reduced  (B.  23,  3597;  24,  3528;  25, 1714). 

E.  Fischer  (A.  190,  67;  199,  281,  294)  has  given  the  name 
of  hydrazines  to  a  series  of  peculiar  bases,  mostly  liquid  and 


112  IV.   DERIVATIVES  OF  MONOHYDRIO  ALCOHOLS 

closely  resembling  the  amines,  but  containing  two  atoms  oi 
nitrogen  in  the  molecule,  and  differing  from  the  latter  espe- 
cially by  their  capability  of  reducing  Fehling's  solution,  for  the 
most  part  even  in  the  cold,  and  by  the  ease  with  which  they 
are  oxidized.  They  are  derived  from  "Diamide"  or  "Hydra- 
zine",  NH2-NH2  (Curtius  and  Jay,  J.  pr.  Oh.  1889,  (2),  39,  27) 
They  are  formed  by  the  action  of  nascent  hydrogen  on  the 
nitrosamines  (p.  108): 

(CH3)2N.NO  +  4H  =  (CH3)2N.NH2  +  H20. 

Primary,  secondary,  tertiary,  and  quaternary  hydrazines  are 
known,  according  as  1,  2,  3,  or  4  of  the  hydrogen  atoms  in 
NH2«NH2  are  replaced  by  alkyl  groups. 

The  secondary  hydrazines  exist  in  two  isomeric  forms, 
namely,  NHR  •  NHR  arid  NH2  •  NR2,  which  are  known  respec- 
tively as  symmetrical  and  unsymmetrical  secondary  hydrazines. 

Methyl-hydrazine,  CH3.NH.NH2  (cf.  A.  1889,  253,  5).  An 
excessively  hygroscopic  liquid,  which  fumes  in  the  air,  and  has 
an  odour  similar  to  that  of  methylamine.  B.-pt.  87°. 

Ethyl-hydrazine,  C2H5.NH-NH2.  When  di-ethyl  urea  is 
treated  with  nitrous  acl  J  a  nitroso-compound  is  formed,  which, 
on  reduction  with  zinc  dust  and  acetic  acid,  yields  the  so-called 
"  diethyl-semicarbazide  ",  and  this  decomposes,  when  heated 
with  hydrochloric  acid,  into  carbon  dioxide,  ethylamine,  and 
ethyl-hydrazine  : 


2H6 

N(NO).C2H5  \N(NH2).C2H5 

Di-ethyl-urea  Nitroso-compound  Diethyl-semicarbazide. 


Ethyl-hydrazine  is  a  colourless  mobile  liquid  of  ethereal 
and  faintly  ammoniacal  odour,  boiling  at  100°.  It  is  very 
hygroscopic,  forms  white  clouds  with  moist  air,  dissolves  in 
water  and  alcohol  with  evolution  of  heat,  and  corrodes  cork 
and  caoutchouc. 

Diethyl-hydrazine,  (C2H5)2N  •  NH2,  is  prepared  from  di- 
ethylamine  by  transforming  it  into  diethyl-nitrosamine  by 
the  nitrous-acid  reaction,  and  then  reducing  the  latter.  It 
resembles  ethyl-hydrazine  closely: 

(C2H5)2N-NO  +  4H  = 


Tetra-ethyl-tetrazone,    (C2H5)2:N'N:N.N:(C2H5)2, 


PHOSPHINES  113 

colourless,  strongly  basic  oil,  volatile  with  steam,  is  formed 
when  diethyl-hydrazine  is  heated  with  mercuric  oxide. 

The  constitution  of  the  hydrazines  follows  from  their  modes 
of  formation.  Since  in  diethyl-nitrosamine,  (C2H5)2N»NO, 
for  instance,  the  nitroso-group  NO  must  be  attached  to  the 
nitrogen  of  the  amine  and  not  to  the  carbon,  judging  from 
the  ease  with  which  it  can  be  separated  (p.  108),  so  the  same 
linking  of  the  atoms  must  be  assumed  in  the  hydrazines, 
which  are  formed  from  the  nitroso-compounds  by  reduction, 
i.e.  by  exchange  of  0  for  2H.  The  readiness  with  which  di- 
ethyl-hydrazirie  is  oxidized  to  diethylamine,  e.g.  by  alkaline 
cupric  oxide,  is  an  agreement  with  such  a  formula.  The 
hydrazines  are  relatively  stable  towards  reducing  agents. 

For  aliphatic  Diazo  and  Triazo  Compounds,  see  Chap.  LI. 

E.  Alkyl  Derivatives  of  Phosphorus,  Arsenic,  &c. 

1.  PHOSPHORUS 

Just  as  amines  are  derived  from  ammonia,  so  from  phos- 
phuretted  hydrogen,  PH3,  are  derived  primary,  secondary, 
and  tertiary  phosphines  by  the  exchange  of  hydrogen  for 
alkyl  radicals,  and  to  these  must  likewise  be  added  quaternary 
compounds,  the  phosphonium  bases.  The  phosphines  corre- 
spond closely  with  the  amines  in  composition  and  in  some  of 
their  properties,  e.g.  they  are  not  saponifiable.  But  they  differ 
from  them  in  the  following  points : — 

1.  Like  phosphuretted  hydrogen  itself,  the  alkyl  phosphines 
are  only  feebly  basic;  thus  ethyl  phosphine  does  not  affect 
litmus,  and  its  salts  are  decomposed  by  water.     The  salts  of 
the  secondary  and  tertiary  compounds  are  not  decomposed, 
thus  showing  that  the  presence  of  alkyl  radicals  tends  to 
strengthen  the  basic  properties  of  the  compound. 

2.  Like  phosphuretted  hydrogen  they  are  readily  inflam- 
mable, and  they  are  consequently  rapidly  oxidized  in  the  air 
and  readily  take  fire  of  themselves. 

3.  As  the  phosphorus  atom  in  these  compounds  shows  a 
tendency  to  pass'  from  the  ter-  to  the  quinque-valent  state, 
many  of  the  phosphines  behave  as  unsaturated  compounds; 
they  combine  with  oxygen,  sulphur,  halogens,  &c.,  for  ex- 
ample,   (CH3)3PO,   (CH3)3PS,    (CH3)3PC12,   and  a  compound 
(CH3)3P,  CS2,  in  the  form  of  red  plates.     The  products  ob- 
tained on  oxidation  are  characteristic,  and  may  be  regarded 

(B480)  B 


114  IV.   DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 

03  derived  from  phosphoric  acid,  0:P(OH)3,  by  the  replace- 
ment of  one  or  more  OH  groups  by  one  or  more  alkyl  radicals  : 

CHg-PHg,  with  nitric  acid,,  yields  CH3-PO.(OH)2,  methyl  phos- 

phonic  acid. 
(CH3)2PH,  with  nitric  acid,  yields  (CH3)2  •  PO  •  OH,  dimethyl  phos- 

phinic  acid. 
(CH3)3P,  on  oxidation  in  the  air,  yields  (CH3)3PO,  trimethyl  phos- 

phine  oxide. 

4.  Corresponding  with  the  disagreeable  smell  of  phos- 
phuretted  hydrogen,  they  possess  an  excessively  strong 
stupefying  odour;  thus  ethyl  phosphine  has  a  perfectly  over- 
powering smell,  and  excites  on  the  tongue  and  deep  down  in 
the  throat  an  intensely  bitter  taste. 

Formation.  —  1.  The  tertiary  phosphines  and  quaternary 
compounds  are  formed  directly  from  phosphine  and  an  alkyl 
iodide.  (Of.  Amines,  formation  2.) 

PH3  +  3C2H6I  =  P(C2H6)3  + 


2.  According  to  Hofmann  (1871),  primary  and  secondary 
phosphines  are  formed  by  heating  phosphonium  iodide  and  an 
alkyl  iodide  with  zinc  oxide,  e.g.  : 

2C2H6I  +  2PH4I  -f  ZnO  =  2P(C2H6)H2,  HI  +  ZnI2  +  H20. 

They  can  be  separated  from  one  another  by  decomposing 
the  salts  of  the  primary  phosphines  by  water,  as  already 
mentioned. 

3.  The   tertiary   phosphines    are    produced    from    calcium 
phosphide  and  an  alkyl  iodide,  a  reaction  first  observed  by 
Thenard  in  1846; 

4.  Also  from  phosphorus  trichloride  and  zinc  methyl,  or 
magnesium  alkyl  iodides  (Auger  and  Billy,  C.  1904,  139,  597). 

5.  The  phosphonium  salts  are  formed  by  the  combination 
of   tertiary   phosphines   with  an   alkyl    haloid,   and    closely 
resemble  the  corresponding  ammonium  compounds. 

Tri-ethyl  phosphine,  P(C2H5)8,  has  no  alkaline  reaction. 
When  concentrated  it  possesses  a  stupefying,  and  when  dilute 
a  pleasant  hyacinth-like  odour. 

Tetramethyl-  phosphonium  hydroxide,  P(CH8)4OH.  Un- 
like the  analogous  ammonium  hydroxide,  this  compound  de- 
composes into  trimethyl-phosphine  oxide  and  methane  when 
heated:  P(CH3)4OH  =  P(CH3)3O  +  CH4. 

The  tetra-ethyl  compound  decomposes  in  a  similar  manner. 


/,;_  ARSINES  115 

2.  ARSENIC 

The  similarity  of  arsenic  to  phosphorus  and  nitrogen  is 
further  exemplified  by  the  analogous  compounds  which  it 
forms  with  alkyl  radicals.  In  virtue,  however,  of  the  more 
metallic  character  of  arsenic,  it  does  not  show  the  same  ten- 
dency to  combine  with  alkyl  radicals  and  hydrogen  at  the 
same  time,  but  forms  derivatives  containing  alkyl  groups  and 
electro -negative  elements  like  chlorine  or  oxygen.  Arsenic 
analogues  of  methylamine  have  been  recently  prepared,  and 
are  very  unstable.  Trimethyl-arsine,  analogous  to  trimethyl- 
amine  and  trimethylphosphine,  is  well  known.  As  primary 
and  secondary  compounds  we  have  methyl-arsine  dichloride, 
CH3«AsCl2,  dimethyl-arsine  chloride,  (CH3)2AsCl,  and  analo- 
gous substances.  They  are  colourless  liquids  of  stupefying 
odour,  exerting  in  some  cases  an  unbearable  irritating  action 
upon  the  mucous  membrane.  They  do  not  possess  basic  pro- 
perties. In  addition  to  these  there  exist  also  quaternary  com- 
pounds, arsonium  salts,  which  are  exactly  analogous  to  the 
quaternary  phosphonium  salts. 

The  halogen  of  the  chlorine  compounds  is  easily  replaceable 
by  its  equivalent  of  oxygen.  Thus,  corresponding  with  the 
compound  B«AsCl2  there  is  an  oxide  E»AsO  and  a  sulphide 
R.AsS,  and  with  the  chloride  E2AsCl  an  oxide  (R2As)20. 
These  oxides,  liquid  or  solid,  are  compounds  of  stupefying 
odour,  and  behave  like  basic  oxides;  hydrochloric  acid  recon- 
verts them  into  the  corresponding  chlorides. 

Here,  also,  the  tendency  of  arsenic  to  change  from  the 
tervalent  to  the  quinquevalent  state  is  especially  marked. 
The  above  chlorides  and  trimethyl-arsine  itself  all  combine 
with  two  atoms  of  chlorine  to  compounds  of  the  type  AsX§. 
The  above  oxygen  compounds  of  the  type  AsX3  and  also  tri- 
methyl-arsine are  consequently  oxidizable  to  compounds  con- 
taining one  0  atom  or  two  OH  groups  more,  acids  or  oxides 
which  are  also  formed  from  the  chlorides  of  the  type  AsX5 
by  exchange  of  halogen  for  0  or  OH,  e.g.  cacodyl  oxide, 

(Me2As)20,  to  cacodylic  acid,  Me2As<^    .     These  products 

are  therefore  completely  analogous  to   the  phosphonic  and 
phosphinic  acids  and  phosphine  oxides  already  described. 

The  compounds  As(CH3)xClc_x,  of  the  type  AsX5,  when 
heated,  decompose  into  methyl  chloride  and  compounds 
As(CH3)x.1Cl4_x,  of  the  type  AsXg,  this  elimination  of  methyl 


116  IV.   DERIVATIVES   OF  MONOHYDRIC  ALCOHOLS 

chloride  taking  place  the  more  readily  the  fewer  methyl 
groups  are  present  in  the  molecule;  thus  As(CH3)3Cl2  breaks 
up  when  somewhat  strongly  heated,  As(CH3)2Cl3  at  50°,  and 
As(CH3)Cl4  at  0°,  i.e.  the  last-named  is  only  stable  when  in 
a  freezing  -mixture.  When,  therefore,  chlorine  acts  upon 
As(CH3)Cl2  at  the  ordinary  temperature,  the  reaction  appears 
to  be  one  of  direct  exchange  of  alkyl  for  chlorine,  thus  :  — 

As(CH3)Cl2  -f  C12  =  AsCl3  +  CHjCl. 

It  is  interesting  to  note  that,  like  free  "  methyl  "  (CH3  •), 
the  radical  »As(CH3)2  has  no  separate  existence;  cacodyl  pos- 
sesses the  doubled  formula  As2(CH3)4  ("  Di-arsene-disnethyl  rj). 

The  tertiary  arsines  are  formed  : 

1.  From  sodium  arsenide  and  alkyl  iodide  (Cahours  ard 
Riche): 

AsNa3  -f  SCgHfil  =  As(C2H6)3  +  3NaL 


2.  From  arsenious  chloride  and  (a)  zinc  alkyl  (ffofmann),, 
or  (b)  magnesium  alkyl  haloid  (Pfeiffer,  B.  1904,  37,  4620; 
Sauvage,  C.  1904,  139,  674). 

Trimethyl-arsine,  As(CH3)3,  and  triethyl-arsine,  As(C2H5)3, 
are  liquids  sparingly  soluble  in  water.  They  fume  in  the  air, 
and  are  thereby  oxidized  to  tri-methyl-  or  -ethyl-arsine  oxide. 

The  secondary  arsines  are  obtained  from  cacodyl  and 
cacodyl  oxide,  which  are  formed  when  a  mixture  of  potassic 
acetate  and  arsenious  oxide  is  distilled  (Cadet,  1760): 


The  distillate  of  cacodyl  and  cacodyl  oxide  so  obtained, 
and  termed  "  alkarsin  ",  fumes  in  the  air  and  is  spontaneously 
inflammable  (Cadet's  "fuming  arsenical  liquid").  Hydro- 
chloric acid  acts  upon  it  to  form  cacodyl  chloride  (Bunsen, 
1838),  and  caustic-potash  solution  gives  pure  cacodyl  oxide, 
As2(CH3)40,  a  liquid  of  stupefying  odour  which  produces 
nausea  and  unbearable  irritation  of  the  nasal  mucous  mem- 
brane; it  boils  without  decomposition,  and  is  insoluble  in 
water  and  of  neutral  reaction.  It  yields  salts  with  acids, 
e.g.  cacodyl  chloride  with  hydrochloric  acid: 

0(AsMe2)2  +  2HC1  =  2  AsMe2Cl  +  H2O. 

The  chloride  is  a  liquid  of  even  more  stupefying  odour  and 
violent  action  than  the  oxide,  and  its  vapour  is  spontaneously 


STIBINES 


117 


inflammable.  When  heated  with  zinc  clippings  in  an  atmos- 
phere of  carbon  dioxide,  it  yields  the  free  cacodyl,  As2(CH8)4 
(from  /caKw&ys,  "stinking"),  a  colourless  liquid  insoluble  in 
water  and  boiling  undecomposed  at  170°,  and  of  a  horrible 
nauseous  odour  which  produces  vomiting.  It  is  as  readily 
inflammable  in  the  air  as  the  vapour  of  phosphorus,  yielding 
the  oxide  when  slowly  brought  in  contact  with  it,  and  also 
combining  directly  with  sulphur,  chlorine,  &c.  Cacodyl 
plays,  therefore,  even  down  to  the  most  minute  particulars, 
the  part  of  a  simple  electro-positive  element;  it  is  a  true 
"organic  element"  (Bunseri). 

PTT  O 

Cacodylic  acid,        3xAs\'   is  crvstalline>   sduble  in 


water,  odourless,  and  poisonous.     It  forms  crystallizable  salts. 


SUMMARY 


Compounds 
with  Chlorine. 

Oxides. 

Acids. 

Primary  .. 

Methyl- 
arsine 
dichloride, 

Methyl- 
arsine  tetra- 
chloride, 

Methyl- 
arsine 
oxide, 

Methyl- 
arsonic  acid, 
0:AsMe(OH)2. 

AsMeCl2. 

AsMeCl4. 

AsMeO. 

Solid  plates. 

B.-p.  133°. 

B.-p.  95°. 

Secondary 

Cacodyl 
chloride, 

Cacodyl 
trichloride, 

Cacodyl 
oxide, 

Cacodylic 
acid, 

AsMe2Cl. 

AsMe2Cl3. 

(AsMe2)20. 

O:AsMe2-OH. 

B.-p.  100°. 

B.-p.  150°. 

Prisms. 

M.-p.  200°. 

Tertiary... 

Trimethyl- 

Trimethyl- 

Trimethyl- 

arsine, 

arsine 

arsine 

AsMe3. 

dichloride, 

oxide, 

B.-p.  70°. 

AsMe3Cl2. 

AsMe3O. 

Solid. 

3.  ANTIMONY,   BORON,   AND  SILICON  COMPOUNDS 

Antimony  also  forms  compounds  with  the  alkyls  precisely 
similar  to  those  of  arsenic;  primary  and  secondary  compounds 
do  not  exist.  Trimethyl-stibine,  Sb(CH3)3  (Landolt),  is  a 
highly  disagreeable  and  spontaneously  inflammable  liquid  of 
onion-like  smell;  and  Antimony  pentamethyl,  Sb(CH8)5,  an 
oily  liquid  of  weak  odour,  which  can  be  distilled,  and  is  not 


118  IV.    DERIVATIVES   OF  M®ftOHYDRtC  ALCOHOLS 

spontaneously  inflammable.  Tetramethyl  -  stibonium  -  hy- 
droxide, Sb(CHo)4OH,  is  very  like  caustic  potash. 

Bismuth  yields  tri-alkyl  derivatives,  e.g.  Bi(CH3)3,  which 
are  relatively  unstable.  No  bismuthonium  compounds  are 
known. 

Boron  tri-ethyl,  B(C2H5)3  (Frankland),  is  a  spontaneously 
inflammable  liquid  which  burns  with  a  green  flame  with 
deposition  of  much  soot;  and  boron  trimethyl,  B(CH3)3,  an 
analogous  gas  of  an  unbearable  stinking  smell. 

The  silicon  compounds  (Friedel  and  Crafts),  in  contradis- 
tinction to  the  foregoing,  resemble  methane  and  the  paraffins 
rather  than  the  spontaneously  inflammable  silicon  hydride, 
and  are  very  stable  in  the  air. 

Tetramethyl  silicane,  Si(CH3)4,  is  a  mobile  liquid  similar  to 
pentane,  and  floats  on  water.  Tetraethyl  silicane  or  Silico- 
nonane,  SiEt4,  is  also  known,  and  gives  rise  to  numerous 
derivatives  corresponding  with  those  of  tetraethyl  methane, 
e.g.  SiC8H19Cl,  SiC8H19.O.CO-CH3,  SiC8H19-OH,  Silicononyl 
alcohol,  &c.  Compare  B.  1911,  44,  2640. 

F.  Organo-Metallie  Compounds 

Most  of  the  important  metals  form  definite  compounds  with 
alkyl  groups.  The  composition  of  these  organo-metallic  or 
metallo-organic  compounds  almost  always  corresponds  with 
that  of  the  metallic  chlorides  from  which  they  are  derived 
by  the  replacement  of  halogen  by  alkyl.  They  are  colourless, 
mobile  liquids  which  boil  without  decomposition  at  relatively 
low  temperatures;  they  often  decompose  violently  with  water 
and  burn  explosively  in  the  air,  but  in  other  cases  they  are 
stable,  both  in  water  and  air.  To  the  former  category  belong 
the  magnesium,  zinc,  and  aluminium  alkyls,  and  to  the  latter 
the  mercury,  lead,  and  tin  compounds.  As  most  of  the  com- 
pour^s  are  volatile,  their  molecular  weights  can  be  deter- 
mined, and  hence  the  valencies  of  the  respective  metals  deter- 
mined, as,  the  alkyl  radicals  are  monovalent.  Examples  are : 
ZnMe2,  CdMe2,  HgEt2,  AlMe3,  PbMe4,  SnEt4,  &c. 

Compounds  are  also  known  which  contain  halogen  as  well 
as  alkyl  radicals  combined  with  a  metal.  They  behave  like 
salts.  The  halogen  in  them  can  be  replaced  by  hydroxyl, 
whereby  basic  compounds  result,  compounds  which  are  often 
much  more  strongly  basic  than  the  corresponding  metallic 
hydroxides,  in  accordance  with  the  electro-positive  character 


O&GANO-METALLIC  COMPOUNDS  119 

of  the  alcohol  radical.     Such  hydroxides  or  oxides  cannot  be 
volatilized  without  decomposition.     Compounds  of  this  type, 
e.g.  CH3»Mg-I,  are  very  readily  prepared  from  their  com- 
ments  (Mg  +  CH3I)   in   dry   ethereal    solution,   and  are 
ily  made  use  of  as  synthetical  reagents. 
tie  organo-metallic  compound  may  be  prepared  — 
1.  By  treating  the  alkyl  haloid  with  the  metal  in  question- 
In  this  way  zinc-,  magnesium-,  and  mercury-alky  Is  are  got: 

=  Mg(CH3)2  +  MgI2. 


The  mixed  organo-metallic  compounds  (p.  121),  e.g.  CH3'Mg-I 
or  C2H5'Zn'I,  are  probably  formed  as  intermediate  products. 
2.  Numerous  metallic  compounds  have  been  prepared  by 
double  decomposition  between  zinc-alkyl  and  the  metallic 
chloride,  or  more  recently  by  the  action  of  the  mixed  mag- 
nesium compounds  on  the  metallic  chloride.  Pfeiffer  (B.  1904, 
37,  319,  1125,  4617)  has  prepared  numerous  tin,  lead,  and 
mercury  compounds  by  this  method: 

2Zn(C2H5)2     +SnCl4    =  Sn(C2H5)4  +  2ZnCl2. 
2C2H6.Mg.I  +  HgCl2  =  Hg( 


Potassium-  and  Sodium  methide,  K(CH3)  and  Na(CH3),  and 
Potassium-  and  Sodium  ethide,  K(C2H5)  and  Na(C2H5),  are 
not  known  in  the  free  state.  When  metallic  sodium  is  added 
to  zinc  ethyl  (or  ethide),  zinc  separates  out  and  a  crystalline 
compound  of  sodium  ethide  and  zinc  ethide  is  formed,  from 
which,  however,  the  former  cannot  be  prepared  pure,  since 
decomposition  sets  in  upon  warming.  On  distilling  in  a  stream 
of  carbon  dioxide,  the  potassium  methide  combines  with  the 
latter  to  form  potassic  .acetate;  the  ethyl  compound  behaves 
in  a  similar  way. 

Zinc  methyl  or  methide,  Zn(CH3)2  (FranHand,   1849),  is 
prepared  according  to  method  1: 
(I)  CH3I  +  Zn  =  Zn(CH3I);    (H)  2Zn(CH3)I  =  Zn(CH3)2  +  ZnI2. 

The  first  stage  is  completed  upon  warming,  and  the  second 
upon  distilling  the  resulting  product.  The  zinc  is  conveniently 
used  in  the  form  of  the  "copper-zinc  couple",  and  the  reaction 
is  facilitated  by  the  addition  of  ethyl  acetate,  the  reason  for 
this  not  being  known.  Zinc  methyl  is  a  colourless,  mobile, 
strongly  refracting  liquid  of  very  piercing  and  repulsive  smell. 


120  IV.   DERIVATIVES  OF  MONOHYDRIC  ALCOHOLS 

B.-pt.  46°;  sp.  gr.  1-39.  It  is  spontaneously  combustible,  and 
burns  with  a  brilliant  reddish-blue  flame  (the  zinc  flame),  with 
formation  of  zinc  oxide,  but  may  be  distilled  in  an  atmosphere 
of  carbon  dioxide.  When  the  supply  of  oxygen  is  limited, 
zinc  methoxide,  Zn(OCH3)2,  is  formed.  It  reacts  violently 
with  water,  yielding  methane  and  Zn(OH)2,  and  with  methyl 
iodide  gives  ethane.  It  is  employed  in  the  preparation  of 
secondary  and  tertiary  alcohols  and  of  ketones.  Iodine  con- 
verts it  into  zinc-methyl  iodide,  ZnCH3I,  white  plates  (see 
above),  and  methyl  iodide;  an  excess  of  iodine  yields  zinc 
iodide  and  methyl  iodide. 

Zinc  ethyl,  Zn(C2H5)2,  b.-pt.  118°,  sp.  gr.  1-18,  closely 
resembles  zinc  methide. 

The  mercury  compounds,  HgMe2  and  HgEt2,  are  produced 
by  method  of  formation  1,  also  by  method  2.  They  are 
colourless  liquids  of  peculiar  sweetish  and  unpleasant  odour, 
and  boil  respectively  at  95°  and  159°.  They  are  permanent 
in  the  air,  but  inflammable,  and  both — especially  the  methyl 
compound — are  very  poisonous. 

Aluminium  methyl,  A1(CH8)3,  is  spontaneously  inflammable 
and  decomposes  violently  with  water.  B.-pt.  130°.  For  vap. 
dens,  see  B.  22,  551. 

Lead  tetramethyl,  Pb(CH3)4,  and  ethyl,  Pb(C2H5)4  (Cahours). 
These  are  formed  according  to  method  2,  curiously  with 
separation  of  lead: 

2PbCl2  +  2Zn(CH3)2  =  Pb(CH3)4 -f  Pb  +  2ZnCa,j. 

They  are  stable  in  the  air,  and  are  interesting  from  the  lead 
in  them  being  tetravalent.  The  hydroxide,  Pb(CH3)3.OH, 
forms  pointed  prisms,  smells  like  mustard,  and  is  a  strong 
alkali;  thus,  it  saponifies  fats,  drives  out  ammonia  from  its 
salts,  precipitates  metallic  salts,  &c.  The  compound  Pb2(C2H5)6 
is  also  known. 

The  tin  compounds  are  similar  (Ladenburg,  Frankland). 

Tin  tetramethyl,  Sn(CH3)4,  Tin  tetraethyl,  Sn(C2H5)4,  Tin 
triethyl,  Sn2(C2H5)6,  Tin  dimethyl,  Sn2(CH3)4,  &c.,  are  of  in- 
terest as  indicating  the  tetravalence  of  tin. 

For  a  number  of  years  the  zinc  alkyl  compounds  were 
largely  used  for  the  synthesis  of  various  groups  of  compounds, 
viz.  hydrocarbons,  tertiary  alcohols,  and  ketones  (see  these). 
To  a  large  extent  these  compounds  are  now  replaced  by  Gri- 
gnard's  reagents  (C.  1900,  130,  1322;  1901,  132,  336,  558). 


V.  ALDEHYDES  AND  KETONES  12l 

Any  alkyl  haloid,  when  added  to  dry  magnesium  powder  sus- 
pended in  pure  anhydrous  ether,  yields  a  compound  of  the 
type  CHg'Mg'I.  This  reaction  occurs  in  ethyl  ether,  amyl 
ether,  and  in  dimethylaniline,  but  not  readily  in  solvents  like 
benzene  unless  ether  or  dimethylaniline  is  also  present.  It 
would  appear  that  the  ether  forms  a  definite  compound,  with 
the  magnesium  alkyl  compound,  of  the  type  CH8«Mg-I, 


(C2H5)20.  Probably  c22'>°<3  (E^er  and 
B.  1902,  35,  1201).  These  Grignard  compounds  in  ethereal 
solution  are  extremely  reactive.  They  have  been  largely  made 
use  of  for  the  preparation  of  hydrocarbons;  primary,  secondary, 
and  tertiary  alcohols;  aldehydes,  acids,  thio-acids,  &c.  (see 
these);  also  for  the  detection  and  estimation  of  hydroxyl 
groups  (B.  1902,  35,  3912,  and  Hibbert  and  Sudborough,  J.  C.  S. 
1904,  85,  933)  by  measuring  the  volume  of  methane  evolved 
when  a  given  weight  of  the  hydroxyl  compound  is  mixed 
with  an  excess  of  the  Grignard  reagent  dissolved  in  amyl  ether. 
They  may  also  be  used  for  differentiating  between  primary, 
secondary,  and  tertiary  amines  (Sudb&rough  and  Hibbert,  Proc. 
1904,  20,  165). 


V.  ALDEHYDES  AND  KETONES,  CJ3J) 

The  aldehydes  and  ketones  are  substances  which  are  re- 
spectively formed  by  the  oxidation  of  the  primary  and 
secondary  alcohols,  the  oxidation  consisting  in  the  elimination 
of  two  atoms  of  hydrogen  from  each  molecule  of  alcohol. 

The  aldehydes  are  formed  from  the  primary  alcohols,  and 
are  easily  converted  by  further  oxidation  into  the  correspond- 
ing acids  containing  an  equal  number  of  carbon  atoms,  oxygen 
being  taken  up.  They  possess  in  consequence  strongly  reduc- 
ing properties. 

The  ketones  result  from  the  oxidation  of  the  secondary 
alcohols,  and  are  more  difficult  to  oxidize  further;  they  do 
not  possess  reducing  properties.  Their  oxidation  does  not 
lead  to  acids  containing  an  equal  number  of  carbon  atoms  in 
the  molecule,  but  to  others  containing  a  smaller  number,  the 
carbon  chain  being  broken. 

The  lower  members  of  both  classes  are  neutral  liquids  of 
peculiar  smell,  readily  soluble  i»  water  and  readily  volatile, 
only  CH20  being  gaseous.  As  the  number  of  carbon  atoms 


122  V.   ALDEHYDES  AND  KETONES 

increases  they  become  less  soluble,  and  their  odour  becomes 
less  marked  with  rise  of  boiling-point  until  the  highest  mem- 
bers are  solid,  odourless  like  paraffin,  and  only  capable  of  being 
distilled  under  reduced  pressure. 

The  aldehydes  closely  resemble  the  ketones  as  regards  modes 
of  formation  and  also  in  many  of  their  properties. 

Both  groups  of  compounds  contain  the  carbonyl  :C:0 
group,  but  in  the  aldehydes  this  is  always  attached  to  a  hy- 
drogen atom,  and  also  to  an  alkyl  group  or  a  second  hydrogen, 
e.g.  CHg.CO-H  and  H-CO-H,  whereas  in  a  ketone  it  is  at- 
tached to  two  alkyl  groups,  e.g.  C2H5  •  CO  •  C2H5. 

A.  Aldehydes 

The  homologous  series  of  the  aldehydes,  CnH2nO,  corre- 
sponds exactly  with  that  of  the  acids,  G^H-^f)^  They  form 
a  group  of  compounds  exactly  intermediate  between  the 
primary  alcohols  and  the  fatty  acids.  Each  primary  alcohol 
by  the  loss  of  hydrogen  yields  an  aldehyde,  and  this  by  the 
addition  of  oxygen  yields  a  fatty  acid  : 


H.CH,.OH 


-2H  +0 


/ 


CH3.CH2-OH  —  CH3.C          —  CH3.Ct,  &c. 


Their  boiling-points  are  decidedly  lower  than  those  of  the 
corresponding  alcohols,  and  rise,  in  the  normal  aldehydes, 
at  first  by  about  27°  for  each  CH2,  and  later  on  by  a  less 
amount. 

Nomenclature.  —  The  name  aldehyde  is  derived  from  alcohol), 
<&%d(rogenatus),  i.e.  an  alcohol  from  which  hydrogen  has 
been  removed.  The  various  aldehydes  are  named  accord- 
ing to  the  acids  to  which  they  give  rise  on  oxidation.  For 
example,  H-CHO  formaldehyde,  CH3»CHO,  acetaldehyde,  &c. 
According  to  the  Geneva  Congress,  the  aldehydes  receive 
names  ending  in  al,  e.g.  ethanal  for  acetaldehyde. 

Modes  of  Formation.  —  1.  By  the  regulated  oxidation  of  the 
primary  alcohols,  CnH^OH,  by  potassium  dichromate  or 
manganese  dioxide  and  dilute  sulphuric  acid;  often  slowly  by 
atmospheric  oxygen,  especially  in  the  presence  of  bone-black 
or  platinum: 


ISOMERISM  OF  ALDEHYDES  123 

2.  From  the  acids  of  the  acetic  series,  by  distilling  a  mixture 
of  their  calcium  or  barium  salts  with  calcium  or  barium  formate 
(Limpricht).     The  foimic  acid  acts  in  this  instance  as  a  reduc- 
ing agent,  producing  calcium  carbonate,  thus: — 

CHg-COOca  -f-  HCOOca  =  CH3.CHO  +  CaCOg.    (ca  =  }  Ca.) 

3.  From  the  dihalogen  substitution  products  of  the  hydrotf 
carbons  containing  the  group  tCHX2,  by  superheating  with 
water  or  by  boiling  with  water  and  PbO: 

CH3.CHC12  +  H2O  =  CH3.CHO  +  2HCL 

4.  From  Grignard  reagents  (p.  120),  and  ethyl  formate  or 
ethyl  orthoformate.     Also  by  heating  alcohols  with  metals  or 
metallic  oxides  (Chap.  XLIX). 

Constitution.  —  In  the  oxidation  of  the  primary  alcohols, 
R.CH2«OH,  to  their  corresponding  acids,  R-CO-OH,  the 
alkyl  radical  R  remains  unaltered.  It  must  consequently  also 
remain  unchanged  in  the  intermediate  products  of  the  oxida- 
tion, viz.  the  aldehydes,  which  therefore  possess  the  constitu- 
tion R-CHO: 

CH3.CH2-OH        CH3.CHO        CHg-CO-OH 

Alcohol  Aldehyde  Acetic  acid. 

The  aldehydes  thus  contain  the  group  «CHO,  either  -C-OH 
or  •  C^TT.  The  former  is  not  correct,  since  the  aldehydes  do 

not  give  the  reactions  characteristic  of  compounds  containing 
hydroxyl  radicals.  All  their  properties  point  to  the  presence 
of  the  :C:0  group.  The  characteristic  grouping  of  all  alde- 
hydes is  thus  the  *C^Q  group.  This  is  confirmed  by  the  fact 
that  an  acid  chloride  R-C<Qj  on  reduction  yields  a  primary 

alcohol  and  undoubtedly  an  aldehyde  as  an  intermediate 
product: 


homers.— Isomerism  in  the  aldehydes  is  caused  solely  by 
isomerism  in  the  alkyl  radicals  R,  which  are  combined  with 
the  group  -CHO,  and 'therefore  contain  an  atom  of  carbon  less. 
Otherwise  the  aldehydes— from  C3Hf)0  on— are  isomeric  with 
the  ketones,  with  the  oxides  of  the  defines  (e.g.  aldehyde  with 


124          V.  ALDEHYDES  AND  KETONES 

ethylene  oxide,  C2H40),  and  with  the  alcohols  of  the  allylic 
series. 

Behaviour.  —  The  aldehydes  are  distinguished  by  being 
exceptionally  chemically  active. 

1.  The  aldehydes  are  very  readily  oxidizable,  slowly  even 
by  the  air  alone,  and  quickly  by  chromic  acid,  salts  of  the 
noble  metals,  &c.     They  consequently  reduce  an  ammoniacal 
solution  of  silver  and  often  one  of  copper;   this  reaction  is 
characteristic  and  is   especially  delicate  in   the   presence  of 
caustic-soda  solution.     (Formation  of  silver  mirror.) 

2.  The  aldehydes  are  easily  reduced  by  nascent  hydrogen, 
e.g.  sodium  amalgam  and  dilute  acid  or  zinc  dust  and  glacial 
acetic  acid,  to   the   primary  alcohols   from  which   they  are 
derived  by  oxidation,  e.g.: 

CH3.CHO  +  2H  =  CH3.CH2.OH. 

A  glycol  is  formed  as  a  by-product,  e.g.  butylene  glycol, 
C4H8(OH)2,  from  C2H4O. 

3.  Phosphorus   pentachloride  and  trichloride  convert  the 
aldehydes  into  ethylidene  chloride   and   analogous   dichloro- 
substitution  products  of  the  hydrocarbons: 

CH3-CHO  — -  CH3.CHC12. 

4.  Additive  reactions.     According  to  Perkin  (J.  C.  S.  1887, 
808),  a  solution  of  acetaldehyde  in  water  contains  a  certain 
amount  of  the  hydrate,  CH3-CH(OH)2.     (Cf.  Chloral  hydrate.) 
This  compound  is  extremely  unstable,  and  has  never  been  iso- 
lated in  a  pure  form.     In  those  reactions  in  which  it  might  be 
formed,  its  anhydride  (acetaldehyde)  is  invariably  produced, 
e.g.  CH3-CHC19  with  alkali  yields  CH3.CH:0  as  final  product, 
and  not  CH.»uH(OH)j,  although  this  is  probably  formed  as 
an  intermediate  substance. 

Thus  we  conclude  that  two  hydroxyl  groups  attached  to  the 
same  carbon  atom  cannot  as  a  rule  exist  together,  but  a  molecule 
of  water  is  eliminated,  and  an  aldehyde  or  ketone  is  formed. 
In  particular  cases  only  can  compounds  with  two  such  hy- 
droxyl groups  exist  (see  Chloral). 

If,  in  place  of  water,  NaHS03,  NH3,  HCN,  &c.,  be  employed, 
direct  addition  to  the  aldehydes  is  readily  observed,  and  in 
all  these  reactions  it  is  concluded  that  the  addition  occurs  at 
the  expense  of  the  doubly-united  oxygen  atom.  A  hydrogen 
atom  of  the  substance  in  question  attaches  itself  to  the  oxygen 
of  the  aldehyde,  with  formation  of  a  hydroxyl  group,  while 


ADDITIVE  COMPOUNDS  OF  ALDEHYDES  125 

the  residual  X  (e.g.  NH2),  which  was  originally  bound  to  the 
afore-mentioned  H  atom,  becomes  united  to  the  carbon: 

CH3-CH: 

Cf.  additive  reactions  of  the  defines  (p.  44). 
The  most  important  additive  reactions  are:  — 

(a)  Combination  with  water,  which  would  lead  to  a  dihydric 
alcohol,  does  not  as  a  rule  take  place,  for  the  reasons  already 
given.     Should  the  alkyl  radical  of  the  aldehyde,  however, 
contain  several  negative  atoms,  e.g.  Cl,  then  the  hydrates  are 
capable  of  existence,  for  instance  chloral  hydrate: 

CC13.CHO  +  H2O  =  CC13.CH(OH)2. 

But  even  in  these  cases  the  tendency  for  water  to  separate 
is  too  great  to  allow  of  such  hydrates  behaving  as  dihydric 
alcohols;  they  react  rather,  for  the  most  part,  exactly  like  the 
aldehydes  themselves.  (Cf.  Pyroracemic  and  Mesoxalic  acids.) 

(b)  Occasionally,  compounds  with  alcohol  or  acetic  acid,  e.g. 
R.CH(OEt)(OH),  or  R.QH(OH)(OAc),  are  met  with.     They 
are,   however,  extremely  unstable.      When  the  aldehyde  is 
heated  with  alcohol  or  acetic  anhydride,  stable  ethers  or  esters 
of  the  hypothetical  glycols  are  obtained  : 


CH3.CHO  +  2C2H5.OH  =  CH3.CH(OC2H6)2  +  H2O. 
CH3.CHO  +  (C2H30)20    =  CH3.CH(OC2H302)2. 

The  compounds  obtained  from  alcohols,  the  so  -  called 
"acetals"  (see  p.  129),  are  also  formed  by  the  partial  oxidation 
of  primary  alcohols,  and  are  hydrolysed  by  sulphuric  acid. 

(c)  The  aldehydes  combine  wit^i  sodium  hydrogen  sulphite, 
NaHS03,  &c.,  to  crystalline  compounds,  readily  soluble  in  water 
but  sparingly  in  alcohol,  e.g.  C2H40,  NaHS03,  JH20.     These 
are  to  be  regarded  as  sulphite  derivatives  of  the  ethylidene 
glycols,   for  instan^,   CH8.CH(OH)(.O.S02Na).     They  are 
almost  invariably  decomposed  when  heated  with  alkalis  or 
acids  and  regenerate   the   aldehydes.     They  are,  therefore, 
of  great  importance  for  the  separation   of  aldehydes  from 
mixtures. 

(d)  The   aldehydes   combine   with  ammonia  to  aldehyde- 
ammonias,  e.g.  aldehyde-ammonia,  (CH3.CHO,NH3)3.    These 
are  crystalline  compounds,  for  the  most  part  readily  soluble  m 
water,  sparingly  in  alcohol,  and  insoluble  in  ether.     Like  the 
bisulphite  compounds,  they  are  advantageously  used  for  the 


126  V.  ALDEHYDES  AND  KETONES 

purification  of  aldehydes,  as  they  readily  yield  the  aldehydes 
when  warmed  with  dilute  acid.     (See  p.  128.) 

(e)  The  aldehydes  combine  with  hydrocyanic  acid  to  form 
nitriles  of  higher  acids;  thus,  acetic  aldehyde  yields  the  com- 

OTT 

pound  CH3«CH<^Q^,  ethylidene  cyanhydrin.     This  reaction 

is  largely  made  use  of  in  the  preparation  of  certain  hydroxy 
acids,  as  the  cyanhydrins,  when  hydrolysed,  yield  hydroxy 

QTT 

acids,  e.g.  CH8»CH<^QQQTT,  lactic  acid. 

(f)  An  interesting  additive  reaction  is  that  between  an 
aldehyde  and  a  Grignard  compound  (p.  121).      Thus  acetal- 

dehyde  and  magnesium  ethyl  iodide  yield  Q  j|  ^>CH  •  OMgl, 

2  OFT 

and  this  with  water  gives  methy  1-ethyl-carbinol,  Q  T|  ^>CH  •  OH^, 

(Cf.  Secondary  Alcohols.) 

5.  The  aldehydes  show  great  tendency  to  polymerize.     (See 
pp.   12   and  45.)      In   the   case  of  formaldehyde  this  poly- 
merization occurs  spontaneously  at  the  ordinary  temperature. 
Acetaldehyde  is  polymerized  upon  the  addition  of  small  quan- 
tities  of   hydrochloric,    sulphuric,   or    sulphurous    acid,  zinc 
chloride,  carbonyl  chloride,   &c.,  to  para-aldehyde,   C6H1203, 
=   (C2H40)3,  at  the  ordinary  temperature,  and  to  meta-alde- 
hyde,  (C2H40)3,  at  0°.     Why  the  above-mentioned  substances 
should  induce  this  polymerization  is  not  known. 

Another  type  of  polymerization  is  the  aldol  condensation 
(see  pp.  127  and  131). 

6.  Towards  alkalis  the  aldehydes  behave  differently.    Alde- 
hyde and  several  of  its  hornologues,  when  heated  with  caustic- 
soda  solution,  are  transformed   into  a  reddish  -  brown  resin 
termed  aldehyde-resin,  a  product  insoluble  in  water  but  soluble 
in  alcohol,  and  possessing  a  peculiar  odour.     Other  aldehydes 
are  transformed  by  alkalis  into  a  mixture  of  equivalent  amounts 
of  alcohol  and  acid,  thus : — 


2ECOH  -f  H20  = 

7.  The  aldehydes  show  a  great  tendency  to  form  condensation 
products  with  aldehydes,  ketones,  acids,  &c.  (See  Crotonic 
Aldehyde,  Cinnamic  Acid,  &c.) 

(a)  CHo.CHO  +  CHo.CHO    =  CEL-CHiCH-CHO  +  H2O. 
(6)  CH3.CO.CH3-f  E-CHO  =  CH3.CO.CH:CHE  +  H2O. 


TESTS   FOR  ALDEHYDES  127 

It  is  probable  that  in  all  these  condensations  direct  addition 
first  occurs  ;  for  example,  in  (a)  aldol,  CH3  •  CH(OH)  .  CH2  •  CHO, 
is  first  formed,  and  then  by  the  loss  of-  water  forms  croton 
aldehyde,  CH3  -  CH  :  CH;  CHO.  (See  p.  131.) 

8.  With  hydroxylamine  the  aldehydes  yield  the  so-called 
Aldoximes,  water  being  eliminated  (V.  Meyer  •,  B.  15,  2778). 

HaiN-OH  =  CH3.CH:N.OH  -fH2O. 


For  the  conditions  under  which  oximes  are  formed,  see  B.  23, 
2769. 

9.  The  aldehydes  react  with   hydrazines  to  form  the  so- 
called  Hydrazones,  water  being  eliminated.     Phenylhydrazine 
is  the  reagent  usually  employed: 

Hg.CHiO  +  Ha-N.NHCA  =  CH3.CH:N.NH.C6H6  +  H2O 

Aldehyde-phenyl-hydrazone. 

Most  of  the  phenylhydrazones  are  somewhat  sparingly 
soluble  in  alcohol,  crystallize  very  readily,  and  are  made  use 
of  in  identifying  different  aldehydes.  On  reduction  they 
yield  primary  amines: 

CH3.CH:N.NH.C6H5-f  4H  =  CH3.CH2.NH2  +  NH2.C6H6. 

10.  Moist  chlorine  and  bromine  act  upon  the  aldehydes  as 
substituents;  thus,  from  acetaldehyde  chloral  is  obtained: 

CH3.CHO  +  3C12  =  CClg-.CHO  +  3HGL 

11.  Sulphuretted  hydrogen  converts  the  aldehydes  into  thio- 
aldehydes.      These   are   compounds    of   unpleasant  aromatic 
odour,  which  show  the  same  peculiarities  of  polymerization  as 
the  aldehydes   (Klinger).     (Cf.  E.  Baumann,  B.  23,  60;   24, 
1419,  3591.) 

Eeactions  8  and  9  may  also  be  regarded  as  condensations. 
It  is  possible  that  in  all  these  reactions  direct  addition  first 
occurs,  and  that  water  is  subsequently  eliminated. 

Tests  for  aldehydes: 

(1)  Behaviour  with  ammoniacal  silver-nitrate  solution  (p.  124, 
and  also  B.  15,  1629). 

(2)  Behaviour  with  alkaline  bisulphites  (p.  125). 

(3)  Behaviour  with  phenyl  -  hydrazine  and  hydroxylamine 
(see  above). 

(4)  Aldehydes  colour  a  solution  of  f  uchsine  which  has  been 


128  V.  ALDEHYDES  AND  KBTONES 

decolorized  by  sulphurous  acid  (Schi/'s  reagent)  an  intense 
violet-red;  some  ketones  and  chloral,  but  not  chloral  hydrate, 
produce  the  same  effect.  (B.  13,  2343;  Bull.  Soc.  Chim. 
1894,  11,  692.) 

Formaldehyde,  Methanal,  H«CH:0,  may  be  regarded  as  the 
oxide  of  the  divalent  methylene  radical,  CH2:.  It  is  obtained 
dissolved  in  water  and  excess  of  methyl  alcohol  by  leading  the 
vapour  of  the  latter,  mixed  with  air,  over  a  glowing  platinum 
or  copper  spiral  or  platinum  asbestos  (Hofmann,  1869).  Other 
oxidizing  agents  lead  directly  to  formic  acid. 

It  is  a  gas,  condensible  by  cold  to  a  clear  mobile  liquid, 
which  boils  at  —21°.  A  solution  of  about  40  per  cent  is  an 
article  of  trade,  and  is  known  as  formalin.  In  solution  it  has 
apparently  the  hydrate  formula,  CH2(OH)2,  and  is  used  as  an 
antiseptic  and  disinfectant. 

Its  chief  polymeric  forms  are : 

(1)  Para-formaldehyde,  probably  (CH20)2,  a  white  mass 
soluble  in  water;  (2)  trioxy-methylene,  probably  (CH20)8,  a 
crystalline  compound  which  passes  into  formaldehyde  again 
when  volatilized;  (3)  formose  (which  see),  a  mixture  of  several 
compounds  of  the  nature  of  glucose.  On  account  of  this  facility 
for  undergoing  polymerization,  formic  aldehyde  in  all  proba- 
bility plays  an  important  part  in  assimilation  by  plants. 

It  does  not  form  an  additive  compound  with  ammonia,  but  con- 
denses to  the  complex  compound  C6H12N4,  hexamethyleneamine. 

By  its  combination  with  hydrochloric  acid,  chloro -methyl 
alcohol  (chloro -metlianol),  CH2C1(OH),  and  hydroxy-chloro- 
methyl  ether  (cUoromethane-oxy-methanol),  CH2C1  •  0  •  CH2OH, 
are  formed.  Both  of  these  are  colourless  liquids,  which  react 
in  many  respects  like  formic  aldehyde  itself. 

Methylal,  CH2(OCH3)2  (see  Acetals,  p.  125),  is  frequently 
made  use  of  instead  of  formaldehyde,  for  carrying  out  conden- 
sation reactions.  It  is  employed  in  medicine  as  a  soporific, 
and  is  also  used  as  an  extractive  for  certain  scents.  B.-pt.  42°. 

Acetaldehyde,  Ethanal,  Aldehyde,  CH3«CHO,  was  formerly 
termed  "acetyl  hydride",  C2H30»H  (Fourcroy  and  Vauquelin, 
1800;  composition  established  by  LieUg  in  1835).  It  is  pre- 
pared by  passing  ammonia  gas  into  an  ethereal  solution  of  the 
crude  aldehyde,  obtained  by  oxidizing  alcohol  with  K2Cr2Or 
-f-  H2S04  and  drying  over  CaCl2,  washing  the  precipitated 
aldehyde-ammonia  with  ether,  and  finally  distilling  it  with 
dilute  sulphuric  acid.  It  is  obtained  in  large  quantity  as  a  by- 
product in  the  first  portions  of  the  distillate  "  First  Runnings  " 


ACETAL,  'CHLORAL,  ETC.  129 

in  the  manufacture  of  spirit.  For  its  production  in  place  of 
vinyl  alcohol,  C2H3»OH,  from  acetylene,  see  pp.  50  and  81. 

It  is  a  colourless  mobile  liquid,  boils  at  21°,  and  has  sp.  gr. 
about  0'8.  Its  odour  is  aromatic  and  suffocating,  and  pro- 
duces a  kind  of  cramp  in  the  chest  when  inhaled.  It  burns 
with  a  luminous  flame,  dissolves  sulphur,  phosphorus,  and 
iodine,  and  is  readily  soluble  in  water,  alcohol,  and  ether. 

Para-aldehyde,  C6H]203,  is  a  liquid  sparingly  soluble  in 
water.  It  melts  at  10°,  and  boils  at  124°,  i.e.  more  than  100° 
above  that  of  aldehyde,  and  is  used  as  a  soporific. 

Meta-aldehyde,  (C2H4O3)8,  crystallizes  in  white  prisms  in- 
soluble in  water,  j,nd  sublimes  at  a  little  over  100°,  but  is 
partially  reconverted  into  aldehyde.  (B.  14,  2271;  40,  4341.) 

Meta-aldehyde  is  changed  back  again  into  ordinary  alde- 
hyde by  prolonged  heating  to  115°  in  sealed  tubes,  and  also, 
as  is  the  case  with  para-aldehyde,  by  distillation  with  some- 
what dilute  sulphuric  acid.  Para-aldehyde  reacts  in  the  same 
way  as  ordinary  aldehyde  with  PC15,  but  not  with  NH3, 
NaHS03,  AgN03,  and  NH2OH.  The  constitution  of  para- 
aldehyde  may  be  represented  as: 

0  (KdnM  and  Zincke). 

(The  union  of  three  molecules  of  aldehyde  by  means  of  the 
valencies  of  carbon  atoms  cannot  be  assumed,  on  account  of  the 
readiness  with  which  para-aldehyde  breaks  up  into  aldehyde.) 

With  regard  to  these  and  other  polymeric  compounds,  the 
general  rule  has  been  proved  to  hold  that,  in  the  case  of  bodies 
of  similar  constitution,  the  one  of  simpler  composition  is  the 
more  soluble,  possesses  the  lower  melting-point,  and  is  the 
more  easily  vaporized. 

Acetal,  CH3.CH(OC2H5)2,  boils  at  104°.  It  is  usually  ob- 
tained by  the  partial  oxidation  of  ethyl  alcohol  with  man- 
ganese dioxide  and  sulphuric  acid,  the  acetaldehyde  first 
formed  condensing  with  the  alcohol  with  the  production  of 
acetal.  This,  as  well  as  methylal,  is  frequently  used  instead 
of  aldehyde  for  the  carrying  out  of  condensation  reactions  (see 
p.  126). 

Propylaldehyde,  C2H5.CHO,  is  present  in  wood-tar.  Nor- 
mal heptylic  aldehyde  (cenanthol),  C7H140,  is  obtained  by  the 
dry  distillation  of  castor-oil  under  diminished  pressure,  &c. 

Chloral,  2  -  trichloro  -  ethanal,  CC13-CHO,  is  a  liquid  which 
boils  at  98°,  and  which— when  impure— easily  changes  into 

(B480)  J 


130  V.  ALDEHYDES  AND  KETONES 

a  solid  polymeric  modification,  meta-chloral,  hut  is  regenerated 
from  this  upon  heating.  It  combines  readily  with  water  to 
chloral  hydrate,  CC13.CH(OH)2  (see  p.  125,  a),  and  with 
alcohol  to  chloral  alcoholate,  CC13  .  CH(OH)(OC2H5),  and  tri- 
chloro-acetal,  CC13.CH(O.C2H5)2.  The  end  product  of  the 
action  of  chlorine  upon  alcohol  consists  chiefly  of  the  last  three 
substances.  They  are  all  colourless  crystalline  compounds, 
which  are  converted  into  chloral  by  distilling  with  sulphuric 
acid,  and  rectifying  over  lime. 

Chloral  is  an  oily  liquid  with  a  sharp,  characteristic  odour. 
It  combines  with  sodium  bisulphite,  ammonia,  hydrocyanic 
acid,  and  acetic  anhydride,  and  reduces  an  ammoniacal  solution 
of  silver  oxide.  It  is  readily  oxidized  to  trichloracetic  acid, 
and  decomposed  by  alkali  into  chloroform  and  an  alkali  for- 
mate: 

CC13-CHO  +  HKO  =  CC13H  -f 


Chloral  hydrate,  CC18  •  CH(OH)2,  forms  large  colourless 
crystals  readily  soluble  in  water,  melting  at  57°,  and  boiling 
with  dissociation  at  97°.  It  acts  as  a  soporific  and  antiseptic 
Sulphuric  acid  converts  it  into  chloral. 

UNSATURATED  ALDEHYDES 

Acrolein,  Acrylic  aldehyde,  propenal,  CH2:CH'CHO,  is  pro- 
duced by  the  oxidation  of  allyl  alcohol,  by  the  distillation  of 
fats,  and  by  heating  glycerol  with  potassium  hydrogen  sulphate. 
It  is  a  liquid  boiling  at  52°,  of  pungent  odour  (the  smell  of 
burning  fat  being  due  to  it),  and  of  violent  action  upon  the 
mucous  membrane  of  the  eyes.  It  unites  in  itself  the  proper- 
ties of  an  aldehyde  and  of  an  unsaturated  carbon  compound, 
and  therefore  combines  with  ammonia  and  with  bromine;  it 
also  unites  with  hydrogen  bromide  to  bromopropyl  aldehyde, 
CH2Br.CH2.CHO. 

When  distilled,  acrolein  -  ammonia  yields  picoline,  C6H7N 
(see  Pyridine  bases);  and  crotonic  aldehyde-ammonia,  by  an 
analogous  reaction,  collidine,  C8HUN. 

Acrolein  can  combine  with  two  atoms  of  bromine  to  acrolein 
dibromide  (dibromopropyl  aldehyde),  CH2Br  •  CHBr  •  CHO,  a 
compound  which  is  of  importance  in  the  synthesis  of  the 
sugars.  (See  Synthesis  of  Monoses.) 

Crotonic  aldehyde,  CH^CHiCH-CHO.  When  acetal- 
dehyde  is  left  for  some  time  in  contact  with  dilute  hydro- 
chloric acid  or  sodium  hydroxide,  polymerization  occurs,  and 


FORMATION   OF  KETONES  131 

a  substance  termed  aldol,  or  a-hydroxy-butyraldehyde,  is 
obtained,  CHS  •  CH(OH)  .  CH2  .  CHO.  The  constitution  of 
aldol  follows  from  its  properties.  It  cannot  be  readily  con- 
verted back  into  acetaldehyde,  and  in  this  respect  differs  from 
the  other  polymeric  forms,  viz.  meta-  and  para-aldehyde.  This 
difference  is  due  to  the  fact  that  in  the  aldol  condensation 
the  union  of  the  molecules  has  been  brought  about  between 
carbon  atoms,  and  hence  the  relative  stability.  Aldol  when 
distilled  or  in  presence  of  dehydrating  agents  yields  croton- 
aldehyde,  water  being  eliminated. 

CH3.CH(OH).CH2.CHO  =  CH3.CH:CH.CHO  +  H2O. 
On  oxidation  it  yields  crotonic  acid. 

B.  Ketones 

The  lowest  member  of  the  series,  Acetone,  contains  three 
atoms  of  carbon.  The  higher  members,  from  C12  on,  are  solid. 
They  are  all  lighter  than  water;  e.g.  the  sp.  gr.  of  acetone  is 
0-81  at  0°. 

Occurrence.  —  Acetone  is  present  in  urine,  methyl-nonyl  ketone 
in  oil  of  rue  (Ruta  graveolens). 

Modes  of  Formation.  —  1.  By  the  oxidation  of  secondary 
alcohols;  just  as  in  the  conversion  of  a  primary  alcohol  to 
an  aldehyde,  this  oxidation  consists  in  the  withdrawal  of 
two  hydrogen  atoms  from  each  molecule  of  the  alcohol: 

CH3.CH(OH).CHS  +  O  =  CH3.CO.CH3  +  H20 

Iiopropyl  alcohol  Acetone. 

Many  primary  and  secondary  alcohols  are  decomposed  into 
hydrogen  and  aldehyde  (or  ketone)  when  heated  in  contact 
with  a  catalyst  (see  Chap.  XLIX). 

2.  By  the  dry  distillation  of  the  calcium  or  barium  salts 
of  fatty  acids,  the  metallic  carbonate  being  also  formed: 


Some  of  the  ketones  of  high  molecular  weight  may  be  ob- 
tained by  heating  fatty  acids  with  phosphorus  pentoxide 
(Kipping): 


132  V.  ALDEHYDES  AND  KETONES 

When  two  different  acids  are  employed,  mixed  ketones,  i  e, 
ketones  containing  different  alkyl  radicals,  are  formed,  thus  :— 


Calcium  acetate  and  propionate  Methyl-ethyl  ketone. 

As  a  rule,  in  addition  to  the  mixed  ketone,  the  two  simpl( 
ketones,  e.g.  (CH8)2CO  and  (C2H5)2CO,  are  also  formed. 

3.  From  dichlorides  containing  the  group  C«CC12»C: 

(CH3)2CC12  +  HaO  =  (CH3)2CO  +  2HC1 

Acetone  chloride  Acetone. 

It  is  probable  that  the  chlorine  atoms  are  first  replaces 
by  hydroxyls,  yielding  the  glycol,  CMe2(OH)2,  which  imme 
diately  eliminates  H20,  yielding  the  ketone,  CMe20. 

4.  By  the  action  of  zinc  alkyl  upon  an  acid  chloride,  e.g 
acetyl  chloride,  CH3-COC1. 

X)ZnCH3 
An  additive  compound  is  first  formed,  CH3«C^-CH3 

Cl 

which  must  be  quickly  decomposed  by  water,  otherwise  ter 
tiary  alcohols  are  produced: 


OH: 

=  CH3.CO-CH3  +  HCl-f  CH3.Zn.OH. 

\;Ci H; 

This  method  of  formation,  which  was  devised  by  Freund  ii 
1861,  allows  of  the  preparation  of  any  possible  ketone  by  usinj 
the  requisite  zinc  alkyl  and  acid  chloride. 

At  the  same  time  it  elucidates,  together  with  method  2,  tht 
constitution  of  the  ketones  from  the  constitution  of  the  corre 
spending  acids.  Conclusions  regarding  constitution  based  01 
the  latter  method  must  be  accepted  with  a  considerable  amoun 
of  reserve  unless  supported  by  other  arguments,  since  in  re 
actions  which  occur  at  high  temperatures  intramolecular  re 
arrangements  can  readily  occur.  Theoretically,  therefore 
ketones  are  compounds  which  contain  the  carbonyl  group 
CO,  linked  on  both  sides  with  an  alkyl  radical,  R-CO-E.  I 
the  alcohol  radicals  are  the  same,  "simple"  ketones  result 
and  if  different,  "mixed"  ketones.  A  compound  with  les 
than  3  C  atoms  is  thus  impossible, 


NOMENCLATURE  OF  KETONES  133 

Ketones  have  been  synthesised  by  the  action  of  organo- 
magnesium  compounds  on  nitriles  or  acid  amides,  e.g.: 


x  +  E'H,  :   ^ 

and  these  with  water  yield  R-CO-R'.     (Blaise,  C.  1901.  132, 
38,  133,  299.) 

5.  From  the  ketonic  acids  or  their  esters,  e.g.  acetoacetic 
ester,  CH3  •  CO  -  CH2  •  CO  •  OC2H5,  by  warming  with  moderately 
dilute  sulphuric  acid  or  with  dilute  alkalis.     This  important  re- 
action will  be  treated  of  at  greater  length  under  acetoacetic  ester. 

6.  By  the  addition  of  water  to  homologues  of  acetylene, 
CH3.C:CH  +  H20  =  CH3.CO.CH3.      This  reaction  occurs 
at  relatively  high   temperatures,   or  may  be  brought   about 
indirectly  by  the  aid  of  sulphuric  acid,  or  solutions  of  mercuric 
salts. 

homers.  —  The  ketones  exhibit  the  same  isomerism  as  the 
secondary  alcohols.  This  isomerism  depends  on  the  one  hand 
upon  the  isomerism  within  the  alkyl  groups,  e.g.  dipropyl 
ketone  and  di-iso-propyl  ketone,  which  are  linked  together  by 
the  CO  group,  and  on  the  other  by  the  position  of  the  oxygen 
atom  in  the  carbon  chain  (position  isomerism)  ;  thus,  C4H9  •  CO  • 
CH3  is  isomeric  with  C3H7  •  CO  •  C2H5. 

The  aldehydes  containing  an  equal  number  of  carbon  atoms 
in  the  molecule  are  always  isomeric  with  the  ketones,  since 
both  classes  of  compounds  are  formed  from  isomeric  alcohols 
by  the  withdrawal  of  2  H. 

Further,  acetone  is  isomeric  with  allyl  alcohol.  Such  an 
isomerism  of  a  saturated  with  an  unsaturated  compound  is 
termed  "saturation  isomerism"  (cf.  p.  87). 

Nomenclature.  —  The  usual  name  is  formed  by  adding  the 
suffix  ketone  to  the  name  of  the  alkyl  groups  present;  e.g. 
(C2H5)2CO,  diethyl  ketone;  CH3-CO.C2H5,  methylethyl 
ketone,  &c.  The  names  of  the  simple  ketones  are  also  derived 
from  the  acids  which  yield  them,  e.g.  "Valerone"  (C4H9)2CO, 
from  valeric  acid. 

The  systematic  names  of  the  ketones  are  formed  by  taking 
the  name  for  the  corresponding  hydrocarbon,  adding  the  suffix 
one  to  indicate  the  O  replacing  "2  H,  and  then  a  number  to 
indicate  the  position  of  the  0  atom,  e.g.  CH8.CO.CH2'CH3, 
butan-2-one,  &c. 


134  V.  ALDEHYDES  AND  KETONES 

Behaviour.  —  1.  Reagents  which  give  rise  to  nascent  hydrogen 
reduce  the  ketones  to  secondary  alcohols  :  (CH3)2CO  +  2  H  = 
(CH3)2CH«OH.  Small  amounts  of  pinacones  (see  these)  are 
formed.  at  the  same  time. 

2.  Oxidizing  agents,  e.g.  K2O207,  and  dilute  H2S04,  slowly 
convert  the  ketones  into  acids  or  ketones  containing  a  smaller 
number  of  carbon  atoms  in  the  molecule  (not  —  as  in  the  case 
of  the  aldehydes  —  into  acids  containing  an  equal  number),  the 
carbon  chain  being  broken: 

CH3.CO.CH3  +  40  =  C 


Since  the  carbon  atom  is  tetravalent,  the  CO  group  in  the 
ketone,  being  already  linked  to  2  alkyl  radicals,  can  only  yield 
the  COOH  group,  characteristic  of  acids  (p.  140),  by  the  re- 
moval of  one  of  the  alkyl  groups.  In  this  process  of  oxidation 
of  a  mixed  ketone  the  molecule  usually  becomes  ruptured  in 
such  a  manner  that  the  CO  group  remains  attached  to  the 
smaller  alkyl  group.  Thus  CH3  •  CO:  •  C3IL  on  oxidation  yields 
mainly  acetic  CH3»C02H  and  propionic  CoH5»C02H  acids;  but 
at  the  same  time  a  small  amount  is  oxidized  to  a  mixture  of 
carbonic  and  butyric  acids  (B.  25,  R.  121). 

Since  the  acids  formed  by  oxidation  bear  no  reciprocal 
relation  to  the  ketone,  and  the  oxidation  process  is  more 
complicated  than  in  the  case  of  the  aldehydes,  it  is  easy  to 
understand  why  the  ketones  do  not  possess  reducing  pro- 
perties. 

3.  Phosphorus  pentachloride,  PC15,  converts  the  ketones 
into  the  corresponding  dichlorides,  acetone,  for  instance,  into 
acetone  chloride,  (CH3)2CC12. 

4.  Additive  reactions,      (a)  The  ketones  do  not  as  a  rule 
combine  with  water  and  alcohol,  for  the  reasons  given  under 
the  aldehydes  and  at  p.  132. 

(b)  With  ammonia  they  yield  complex  condensation   pro- 
ducts,  e.g.  di  -  acetone  -  amine,   C6H13NO,   tri  -  acetone  -  amine, 
CgH^NO  (Heintz)  ;  this  reaction  is  more  complicated  than  that 
with  the  aldehydes,  2  or  3  molecules  of  acetone  combining 
with  1  molecule  of  ammonia,  with  elimination  of  water. 

(c)  The  ketones  which  contain  the  group  CH8»CO«,  and 
a  few  other  relatively  simple  ketones,  combine  with  sodium 
hydrogen  sulphite  to  crystalline  compounds,  e.g.  acetone  tc 

(CH8)2C<\Q  OQ  -AT  ,  H20,  which  can  be  converted  back  intc 
the  ketone  by  distillation  with  sodium-carbonate  solution.    This 


REACTIONS  OF  KETONES  136 

very  important  reaction  is  made  use  of  in  separating  and  puri- 
fying the  ketones.  Stewart  has  recently  (J.  C.  S.  1905,  87,  185) 
studied  the  comparative  rates  at  which  some  of  these  compounds 
are  formed. 

(d)  With  hydrocyanic  acid  they  yield  hydroxy-nitriles,  as 

in  the  case  of  the  aldehydes;  e.g.  (GE^fk^- 

(e)  Ketones  readily  form  additive  compounds  with  Grignartfs 
reagents,  and  when  decomposed  with  water  these  yield  tertiary 
alcohols  (see  p.  72)  : 


Me2CO  +  MeMgI 

H  =  Me3C.OH  +  OH-Mg-I. 


5.  The  ketones,  unlike  the  aldehydes,  do  not  possess  the 
property  of  polymerizing,  but  they  form  condensation  products. 
Just  as  aldehyde  is  converted  into  crotonic  aldehyde,  so  is 
acetone,  by  the  action  of  many  reagents  —  e.g.  CaO,  KOH,  HC1, 
and  H2S04  —  converted,  with  elimination  of  water,  into  mesityl 
oxide,  C6H100,  phorone,  C9HU0,  or  mesitylene,  C9H12,  accord- 
ing to  the  conditions  (see  these  substances): 

203^0  =  C6H100  +  H2O.  .      3C3H60  =  C9HUO  -}-  2H2O. 
3C3H6O  =  C9H12  +  3H2O. 

Analogous  condensations  also  ensue  with  other  ketones  or 
aldehydes  under  the  influence  of  dilute  caustic  soda  or  of 
sodium  ethoxide  (B.  20,  655).  In  this  way  the  more  compli- 
cated ketones  are  formed  (A.  218,  121). 

6.  Sulphuretted  hydrogen  converts  the  ketones  into  thio- 
compounds,  e.g.  acetone  into  thio-acetone,  CH3-CS'CH3  (B. 
16,  1368),  or  their  polymers. 

7.  Halogens  give  rise  to  substitution  products. 

8.  Like  the  aldehydes,  the  ketones—  even  C35—  react  with 
hydroxylamine,  yielding  oximes,  which  are  termed  Ketoximes 
(V.  Meyer,  B.  15,  1324,  2778;  16,  823,  1784,  &c.): 

(CH3)2C:p+'H2;N.OH  =  H2O  +  (CH3)2C:N.OH(acetoxime). 

9.  They  react  in  an  analogous  manner  with  phenyl-hydrazine, 
C6H5.NH.NH2  (E.  Fischer,  B.  17,  572),  with  the  formation  of 
phenyl-hydrazones  (p.  127): 

(CH3>2C:N.NH.C6H6  +  H80. 

Aceton  e-phenyl-hy  drazone. 


136          V.  ALDEHYDES  AND  KETONES 

Phenyl-hydrazine  and  hydroxylamine  are  therefore  of  great 
value  for  the  recognition  of  the  aldehydic  or  ketonic  character 
of  a  substance.  Semicarbazide,  NH2.CO-NH«NH2,  reacts  in 
an  analogous  manner  (A.  1898,  303/79),  and  it  or  its  hydro- 
chloride  is  now  largely  used  as  a  reagent  for  aldehydes  and 
ketones,  as  the  products  (semicarbazones)  crystallize  well  and 
have  definite  melting-points: 

(CH3)2CO  +  NH2.NH.(X).NH2 

=  H20  +  (CH3)2C :  N  •  NH  •  CO  •  NH2. 

Acetaldehyde-semicarbazone  melts  at  162°,  and  acetone-semi 
carbazone  at  187°. 

10.  Nitrous  acid  (ethyl  nitrite  and  sodium  ethylate)  gives 
rise  to  iso-nitroso-ketones,  e.g.  iso-nitroso-acetone,  CH3-CO' 
CH:N«OH,  by  replacement  of  H2  by  the  group  :N*OH 
(oximino).  When  hydrolysed,  the  :N»OH  group  is  replaced 
by  oxygen,  and  diketones  or  aldehydo-ketones  are  formed. 

Acetone,  2-Propanone,  CH3»CO»CH3.  The  formula  was 
established  by  Liebig  and  Dumas  in  1832.  It  is  present  in 
very  small  quantity  in  normal  urine,  in  the  blood,  in  serum, 
&c.,  but  in  much  larger  quantity  in  pathological  cases  such  as 
acetonuria  and  diabetes  mellitus.  It  is  produced,  among  other 
ways,  by  the  distillation  of  sugar,  gum,  cellulose,  &c.,  and  is 
therefore  present  in  wood  spirit;  also  by  the  addition  of  water 
oo  allylene,  C3H4  (p.  50).  On  the  large  scale  it  is  prepared  by 
the  dry  distillation  of  calcium  acetate. 

It  is  a  liquid  of  peculiar  pungent  odour j  boils  at  56°,  and 
has  sp.  gr.  0*81  at  0°.  It  is  soluble  in  water,  but  may  be 
salted  out  from  its  aqueous  solution,  and  is  also  miscible  with 
alcohol  and  ether.  KMn04  does  not  oxidize  it  in  the  cold,  but 
Cr03  converts  it  into  acetic  and  carbonic  acids. 

Metallic  sodium  reacts  with  acetone,  yielding  the  derivative 
CH8.C(ONa):CH2. 

Detection. — Acetone  may  be  detected  by  the  formation  of 
indigo  when  its  solution  in  sodium  hydroxide  is  warmed  with 
o-nitro-benzaldehyde. 

Sulphonal,  (CH3)2 :  C(S02  •  C2H5)2,  is  formed  when  a  mixture 
of  acetone  and  mercaptan  is  treated  with  hydrochloric  acid, 
and  the  mercaptol,  (CH3)2C(SC2H5)2  [a  derivative  of  the 
hypothetical  acetone-glycol,  (CH3)2C(OH)2],  which  is  thus 
formed,  is  oxidized  by  potassium  permanganate  to  the  corre- 
sponding sulphone.  It  crystallizes  in  prisms,  melts  at  125° 
and  acts  as  a  soporific. 


ALDOXIMES  AND   KETOXIMES  137 

Mesityl  oxide,  C6H100,    =    CH3 .  CO  •  OH :  C(CH3).2  (Kane, 
1838;  Baeyer),  is  a  liquid  of  aromatic  odour,  boiling  at  132°. 


Phorone,  C9H140,  =  (CH3)2C :  CH .  CO .  CH :  C(CH3)2,  forms 
readily  fusible  yellow  crystals.  Both  of  these  compounds  are 
obtained  by  saturating  acetone  with  hydrochloric  acid  gas  (A. 
180,  1). 

Methyl  ethyl  ketone  (2-Butanone),  CH3«CO'C2H5,  is  present 
in  crude  wood  spirit,  and  is  also  formed  by  the  oxidation  of 
secondary  butyl  alcohol.  B.-pt.  81°. 

Pinacoline  (2-Dimethyl-3-bufanone),  methyl  tertiary-butyl  ketone, 
CH3  •  CO  •  C(CH3)3,  is  produced  by  the  action  of  dilute  sulphuric 
acid  upon  pinacone  (p.  193).  This  involves  a  characteristic 
rearrangement  known  as  the  "pinacoline  reaction".  B.-pt. 
106°. 

A  number  of  ketones  have  been  obtained  from  the  higher 
fatty  acids.  These  have  been  converted  by  Krafft  into  the 
corresponding  paraffins,  by  first  transforming  them  into  the 
chlorides,  CnH2nCl2,  by  means  of  PC15,  and  then  heating  the 
latter  with  hydriodic  acid  and  phosphorus. 

ALDOXIMES  AND  KETOXIMES 

The  aldoximes  and  ketoximes  are  the  compounds  obtained 
by  the  action  of  hydroxylamine  on  the  aldehydes  and  ketones 
respectively.  They  both  contain  the  bivalent  oximino  group 
;  N  •  OH  attached  to  carbon,  e.g. : 

CH3.CH:N.OH    and    (CH3)2C:N.OH 

Acetaldoxime  Acetoxime. 

They  are  either  colourless  crystalline  compounds  or  liquids, 
and  are  both  basic  and  acidic  in  properties.  With  metallic 
hydroxides  they  yield  salts  of  the  type  CH3-CH:NOK;  with 
mineral  acids  they  form  salts  in  much  the  same  manner  as 
ammonia  does,  e.g.  CMe2:NOH,  HC1. 

The  oximes  are  fairly  readily  hydrolysed  by  dilute  acidjs, 
yielding  hydroxylamine  and  either  an  aldehyde  or  a  ketone. 

On  reduction  they  all  yield  primary  amines,  :N  •OH-*«NH2. 

Dehydrating  agents,  e.g.  acetic  anhydride  or  acetyl  chloride, 
transform  the  aldoximes  into  nitriles,  water  being  eliminated: 
GH8.C;H;:Nv()BG  =  CH3.C:N  +  H2O. 

The  ketoximes  with  acetyl  chloride  undergo  an  interesting 
intramolecular  rearrangement  known  as  the  Bedcmann  transfor- 
mation, the  final  product  being  an  acid  amide  or  anilide.  It 


138  V.  ALDEHYDES  AND  KETONES 

is  probable  that  the  hydroxyl  group  of  the  oxime  changes 
place  with  one  of  the  alkyl  groups  attached  to  the  carbon 
atom,  and  this  then  leads  to  a  wandering  of  a  hydrogen  atom 
and  a  shifting  of  the  double  bond: 

R-C-R'  E.G.  OH          K.C:O 

N.OH  "          N.R'  NHR'. 

Constitution.  —  In  the  formation  of  the  oximes  the  water 
eliminated  is  undoubtedly  formed  from  the  oxygen  of  the 
carbonyl  group  and  the  hydrogen  atoms  of  the  hydroxylamine, 
otherwise  the  reaction  would  be  of  the  type 

H2O, 


and  an  aminoketone  would  result.     There  are  two  possible* 
ways  in  which  water  can  be  thus  eliminated,  yielding  a  com 

pound  CMe2:N«OH  or  CMe2<J     .     That  the  first  of  these 
two  formulae  is  correct  is  demonstrated  b    the  fact  that  when 


an  alkyl  derivative,   :C:N»OR  or  :C\  |       ,  is   hydrolysed 

XN-R 

with  hydrochloric  acid  an  alkyl  derivative  of  hydroxylamine, 
NH2'OR,  is  obtained,  and  hence  the  alkyl  group  is  presum- 
ably attached  to  oxygen  in  the  alkylated  oxime,  and  the 
oxime  itself  thus  contains  an  OH  group.  This  constitution 
formula  is  in  perfect  harmony  with  the  reactions  character- 
istic of  oximes. 

The  oxime  derived  from  an  aldehyde  or  ketone  often  exists 
in  isomeric  forms.  This  is  especially  true  of  those  derived  from 
aromatic  aldehydes  and  from  mixed  (unsymmetrical)  ketones 
of  the  aromatic  series.  According  to  Goldschmidt  and  V.  Meyer, 
these  isomers  are  structurally  identical,  and  are  stereo-isomeric 
(i.e.  the  isomerism  is  due  to  the  spatial  relationship  of  the 
various  atoms  and  radicals). 

According  to  Hantzsch  and  Werner,  the  isomerism  is  readily 
explicable  if  we  assume  that  two  of  the  three  valencies  of  the 
nitrogen  atom,  when  N  is  united  by  a  double  bond  to  C,  lie 
in  the  same  plane,  but  that  the  third  valency  lies  outside  this 
plane.  Thus  R.C.H 

N     • 


SATURATED  MONOBASIC  ACIDS  139 

with  the  oxime  derived  from  an  aldehyde,  if  the  two  valencies 
attaching  N  to  C  lie  in  a  plane  at  right  angles  to  the  plane 
of  the  paper,  then  the  OH  radical  must  fall  either  close  to  the 
alkyl  group  R  or  to  the  H  atom;  in  fact,  two  configurations 
are  possible,  viz. : — 

R.C.H          B-C.H 
N.OH      HO.N. 

These  are  known  (1)  as  sy?i-aldoximes  when  the  H  and  OH 
are  close  together,  and  as  a  rule  they  readily  lose  water, 
yielding  nitriles;  (2)  as  anti-aldoximes  when  the  H  and  OH 
are  far  removed  from  one  another.  As  a  rule,  these  yield 
acetyl  derivatives,  and  not  nitriles,  on  treatment  with  acetyl 
chloride. 

The  oximes  derived  from  unsymmetrical  ketones  also  often 
exist  in  stereo-isomeric  forms,  which  can  be  explained  in  a 
similar  manner: 

R-C-R'  R-C-R' 

N.OH          HO-N. 

No  isomerism  should  occur,  and  so  far  none  has  been  met 
with,  in  the  case  of  the  oxime  derived  from  a  symmetrical 
ketone  when  R  =  R'.  The  configurations  of  these  isomeric 
ketoximes  are  generally  derived  from  a  study  of  the  Beckmann 
transformation. 

R.C-R'  R.C-R' 

gives  R  •  CO  •  NHR'  and          ||       gives  NHR  •  CO  •  R 
N-OH  OH-N 

(See  also  Aromatic  Aid  oximes  and  Ketoximes.) 


VI.  MONOBASIC  FATTY  ACIDS 
A.  Saturated  Acids,  C.H.A,  or  CJWCO.H 

(See  Table,  p.  140.) 

The  monobasic  fatty  acids  are  formed  by  the  oxidation  of 
the  saturated  primary  alcohols  or  of  their  corresponding 
aldehydes.  These  acids  are  monobasic,  i.e.  contain  in  the 


140 


VI.   MONOBASIC  FATTY  ACIDS 


molecule  only  one  replaceable  atom  of  hydrogen,  since,  as 
a  rule,  they  give  rise  to  only  one  series  of  salts  or  of  esters. 
They  are  known  as  the  fatty  acids,  because  many  of  them 
are  contained  in  fats  or  are  formed  from  fats  by  processes  of 
oxidation  or  hydrolysis.  They  are  often  spoken  of  as  acids 
of  the  aliphatic  series. 

The   characteristic  group   of   the   monobasic   acids   is   the 


carboxylic  group  'C^Q  TTJ  and  it  is  the  hydrogen  of  this 

group  which  becomes  replaced  in  the  formation  of  salts.  The 
basicity  of  an  acid,  as  a  rule,  depends  on  the  number  of  such 
carboxylic  groups  present  in  the  molecule. 

NORMAL  FATTY  ACIDS  AND  THEIR  PHYSICAL  DATA 
i-COgH,  where  C^H^+i  is  a  normal  alkyl  group. 


Mclting-pt. 

Boiling-pt. 

CHnO. 

8'3° 

101° 

Acetic  acid.         

C9H,O« 

17° 

118° 

Propionic  acid  

CoH.O, 

—  36° 

141° 

Butyric  acid 

C4H8O2 

—  8° 

162° 

Valeric  acid         .    . 

aH,no9 

186° 

Caproic  acid  

CH  0 

+  8° 

205° 

Heptoic  acid 

CH  0 

—  10° 

224° 

Caprylic  acid  

CcHirO, 

-1-  16° 

236° 

CH  0 

12° 

254° 

r  TT  r? 

31° 

269° 

TJndecylic  acid  

C^HgoOo 

28° 

-{213° 

Laurie  acid  

C19H9dO2 

-  43° 

{226° 

Tridecylic  acid 

C  H  0 

40° 

236° 

Mrristic  acid  .        

54° 

248° 

Pentadecylic  acid 

51° 

257° 

Palmitic  acid 

63° 

(269° 

Margaric  acid  

picS3222 

60° 

1277° 

Stearic  acid  

69° 

{287° 

Nondecylic  acid  

C,oHooOo 

66° 

{298° 

A  rachidic  acid     

p  TT  n 

75° 

C  H  0 

83° 

Lignoceric  acid       

cXA 

80° 

78° 

Melissic  acid 

C*H£O! 

90° 

The  lower  members  of  the  series  are  liquids  of  pungent 


FORMATION   OF  FATTY  ACIDS  111 

odour  and  corrosive  action,  and  boil  without  decomposition. 
They  dissolve  readily  in  water,  and  the  aqueous  solutions  exhibit 
a  strongly  acid  reaction,  although  most  of  the  anhydrous  acids 
are  without  action  on  dry  litmus  paper.  The  intermediate 
members  have  an  unpleasant  smell  like  that  of  rancid  butter 
or  perspiration,  and  are  oily  and  but  slightly  soluble  in  water. 
Mobility,  odour,  and  solubility  diminish  as  the  percentage  of 
carbon  increases.  The  higher  members,  from  C10,  are  solids, 
like  paraffin,  insoluble  in  water,  and  can  only  be  distilled 
without  decomposition  in  a  vacuum.  Their  acid  character  no 
longer  finds  expression  in  their  reaction  with  litmus,  but  in 
their  capability  of  forming  salts  with  bases.  These  higher 
acids  are  readily  soluble  in  alcohol,  and  especially  in  ether. 

In  this  series  the  boiling-point  rises  regularly  for  each 
increase  in  the  number  of  0  atoms  in  the  molecule.  The 
rise  is  roughly  19°  for  each  increment  of  CH2.  The  melting- 
points  do  not  exhibit  the  same  regularity:  the  melting-point  of 
any  acid  containing  an  even  number  of  C  atoms  in  the  mole- 
cule is  higher  than  the  melting-point  of  the  acid  with  an  odd 
number  of  C  atoms  which  immediately  succeeds  it. 

Similar  phenomena  have  been  observed  in  other  homologous 
series.  (See  section  on  Physical  Properties  and  Constitu- 
tion.) 

The  specific  gravity  of  the  liquid  acids  is  at  first  >  1,  and 
from  C3  onwards  <  1,  and  it  decreases  continuously  to  about 
0'8,  the  paraffin  character  of  the  hydrocarbon  radical  becoming 
preponderant. 

Occurrence. — Many  of  the  acids  of  this  series  are  found  in 
nature  in  the  free  state,  but  more  frequently  as  esters,  viz.  :— 
(a)  esters  of  monohydric  alcohols  (see  wax  varieties),  (b)  esters 
of  glycerol  or  glycerides,  in  most  of  the  vegetable  and  animal 
fats  and  oils.  For  further  particulars  see  pp.  157  and  158. 

Formation. 1.  By  the  oxidation  of  the  primary  alcohols, 

R.CH2.OH,  or  their  aldehydes,  R.C<Q,  by  means  of  K2Cr2Or 

or  Mn02  and  dilute  H2S04,  or  by  the  oxygen  of  the  air  in 
presence  of  platinum  or  of  nitrogenous  substances,  e.g.  acetic  acid 
from  alcohol.  The  acids  thus  formed  contain  the  same  number 
of  carbon  atoms  as  the  alcohol  or  aldehyde.  Many  complex 
carbon  compounds,  e.g.  ketones,  unsaturated  compounds,  &c., 
when  oxidized  yield  acids  containing  a  smaller  number  of 
carbon  atoms.  The  higher  acids  of  this  series  are  converted 
into  their  lower  homologues  when  oxidized. 


142  VI.   MONOBASIC  FATTY  ACIDS 

2.  Several  acids  have  been  prepared  from  the  halogen  com- 
pounds containing  the  group  »CX8,  e.g. : — 

HCC13  +  4KOH  =  H-COaK  +  3KC1  +  2H2O. 

We  should  expect  an  exchange  of  the  three  chlorine  atoms 
for  three  hydroxyls,  with  formation  of  the  intermediate  com- 
pounds CH(OH)3  or  R«C(OH)8.  Such  compounds  are,  how- 
ever, extremely  unstable,  and  immediately  eliminate  water, 
yielding  the  acids  (cf.  p.  124): 

OH 

:H  = 

But  derivatives  of  these  trihydric  alcohols,  or  ortho-acids  as 
they  are  termed,  are  known;  for  example,  ethyl  ortho-formate, 
HC(OC2H5)3,  a  neutral  liquid  of  aromatic  odour,  insoluble  in 
water,  and  boiling  at  146°. 

3.  From  the  alkyl  cyanides  or  nitriles,  (^EL^CN.     The 
cyanides,  which  are  prepared  by  warming  the  alkyl  iodides 
with  cyanide  of  potassium,  are  converted  into  the  fatty  acids 
and  ammonia  by  hydrolysis  with  potassium  hydroxide  solu- 
tion, with  dilute  or  concentrated  hydrochloric  acid,  or  with 
sulphuric  acid  diluted  with  its  own  volume  of  water. 

The  reaction  may  be  regarded  as  the  addition  of  two  mole- 
cules of  water  to  each  molecule  of  nitrile : 

CHS.C:N  —  CHS.(X).NH2  —  CHa-CO-ONE^ 
+  H20  +H,0 

first  yielding  the  acid  amide,  and  then  the  ammonium  salt  of 
the  acid,  which  is  decomposed  by  the  hydrolysing  agent 
employed.  The  process,  in  the  case  of  aromatic  nitriles,  can  be 
stopped  at  the  point  when  the  acid  amide  is  formed,  but  in 
the  aliphatic  series  this  is  almost  impracticable.  The  reaction 
is  the  exact  reverse  of  the  formation  of  nitriles  from  the 
ammonium  salts  of  fatty  acids: 

CH3.CO-ONH4  —  CH3.CO-NH2  —  CH3.C:N. 
-H20  -H2O 

The  great  importance  of  this  reaction,  by  means  of  which 
we  can  obtain  an  acid  Cn+1  from  an  alcohol  Cn,  has  been 
already  indicated  (p.  101).  And  since  the  acids  can  be  con- 
verted indirectly  by  reduction  into  the  corresponding  alcohols, 


FORMATION   OF  FATTY  ACIDS  143 

it  is  thus  possible  to  build  up  synthetically,  step  by  step,  the 
alcohols  richer  in  carbon  from  those  poorer  in  carbon,  a  cir- 
cumstance which  is  of  especial  importance  in  the  case  of  the 
normal  alcohols  (Lieben  and  Eossi).  As  an  example: 

qa3.OH  —  CH3I  —  CH3.CN  —  CHg-COOH  —  CHg-CHO 

P  and  I          KCN  Hydrolysis  With  calcium 

formate 

—  CH3.QH2OH 

Reduction. 

4.  The  acids  may  be  regarded  as  resulting  from  the  par- 
affins, e.g.  acetic  acid  from  CH4  and  C02,  and  formic  acid  from 
H2  and  C02.     The  two  components  can  be  made  to  combine 
indirectly;  thus,  carbon  dioxide  and  sodium  methyl  (p.  119) 
combine  when  heated  together  (Wanklyn)-. 

CH3Na  +  C02  =  CH3.C02Na. 

Formic  acid  is  obtained  in  an  analogous  manner  from 
hydrogen  and  carbon  dioxide,  under  the  influence  of  the  silent 
electric  discharge: 

H2  +  CO,  =  H.C02H; 

or  from  hydrogen,  potassium,  and  carbon  dioxide,  when  the 
potassium  is  placed  in  a  bell-jar  filled  with  moist  carbon  dioxide 
(Kolbe  and  Schmitt,  1861);  or  by  treating  carbonate  of  am- 
monia, &c.,  with  sodium  amalgam. 

5.  By  passing  carbon  monoxide  over  heated  caustic  alkali 
or  alcoholate,  thus: 

CH3-ONa  -f  CO  =  CH3-C02Na  (at  160°). 
H-ONa  +  CO  =  H.C02Na. 


6.  By  the  action  of  carbon  dioxide  on  ethereal  solutions  of 
organo-magnesium  haloids,  a  magnesium  compound, 

CnH2n+1.Mg.I 


is  obtained,  which  gives  the  free  acid  on  the  addition  of  dilute 
sulphuric  acid  (C.  1904,  138,  1048). 

7.  By  the  addition  of  hydrogen  to  unsaturated  acids,  e.g. 
propionic  acid,  CH3-CH2.C02H,  from  acrylic  acid,  CH2:CH- 
C02H.  This  addition  of  "hydrogen  may  be  effected  (a)  directly 
by  hydriodic  acid  and  phosphorus,  sodium  amalgam  and  water, 
or  by  the  aid  of  hydrogen  and  reduced  nickel  at  a  temperature 
of  about  100°  (Abstr.  1903,  1,  547),  or  hydrogen  and  colloidal 


144  VI.    MONOBASIC   FATTY  ACIDS 

palladium  at  the  ordinary  temperature,  Chap.  XLIX;  (b)  in- 
directly, by  addition  of  hydrobromic  acid  and  inverse  substi- 
tution. Unsaturated  acids  also  yield  saturated  ones  contain- 
ing fewer  carbon  atoms  when  fused  with  potash,  e.g.  1  mol. 
crotonic  acid,  C,H602,  yields  2  mols.  acetic  acid,  C2H402. 

8.  From  the  nydroxy  acids,  by  reduction  with  hydriodic 
acid: 


CH3.CH(OH).C02H  +  2HI  =  CH3.CH2.CO2H  +  I2  -f  H2O 

Lactic  acid  Propionic  acid. 

9.  From  many  polybasic  acids,  by  the  elimination  of  C02, 
for  example,  formic  from  oxalic,  COOH«;COOH,  and  acetic 
from  malonic,  iC02;H  •  CH2  •  C02H. 

10.  Aceto-acetic  ester  syntheses.  —  The  homologues 

R.CH2.COOH  and 

can  be  prepared  from  acetic  acid  by  first  converting  the  latter 
into  aceto-acetic  ester,  CH3  •  CO  •  CH2  •  COOC2H5,  introducing 
alkyl  groups  into  this,  and  then  decomposing  the  compound 
so  obtained  by  concentrated  alcoholic  potash.  (Cf.  Aceto- 
acetic  Ester,  p.  228;  and  Malonic  Ester,  p.  238.) 

Separation.  —  Natural  fats  are  nearly  all  glycerides,  i.e.  esters 
derived  from  the  trihydric  alcohol,  glycerol,  and  various  fatty 
and  other  acids,  so  that  a  mixture  of  acids  is  obtained  when 
any  natural  fat  is  hydrolysed.  This  mixture  may  be  separated 
into  its  components  as  follows  :  — 

(a)  By  fractional  distillation  in  a  good  vacuum;  (b)  by 
fractional  precipitation  of  an  alcoholic  solution  of  the  acids 
by  means  of  magnesium  acetate,  calcium  chloride,  &c.,  the 
acids  richer  in  carbon  being  precipitated  first;  (c)  by  frac- 
tional solution:  the  dry  barium  salts  of  formic,  acetic,  pro- 
pionic,  and  butyric  acids  are  very  differently  soluble  in  alco- 
hol, the  solubility  increasing  rapidly  with  the  number  of 
carbon  atoms;  (d)  by  fractional  neutralization,  and  distillation 
of  the  non-combined  acid. 

Behaviour.  —  1.  Salts.  The  acids  are  monobasic,  and  thus 
form  normal  salts,  e.g.  CHg»C0.2Na.  They  also  yield  acid 
salts  —  the  so-called  per-acid  salts  —  from  the  existence  of 
which  we  might  feel  inclined  to  doubt  their  monobasic  nature. 
These  salts  can,  however,  be  crystallized  from  a  strongly  acid 
solution  only;  they  decompose  on  the  addition  of  water,  and 
a]so  lose  their  excess  of  acid  when  heated.  The  formation  of 


CONSTITUTION   OF  FATTY  ACIDS  145 

such  acid  salts  is  now  usually  regarded  as  being  due  to  the 
tetravalency  of  one  of  the  oxygen  atoms,  e.g.  : 


All  the  other  chemical  characteristics  of  the  acids  go  to  prove 
their  monobasicity,  especially  the  non-formation  of  acid  esters. 

2.  The  monobasic  acids  give  rise  to  different  groups  of  deri- 
vatives in  much  the  same  manner  as  the  monohydric  alcohols. 
The  typical  hydrogen  atom  is  replaceable  by  an  alkyl  group 
with  formation  of  an  ester  or  alkyl  salt,  e.g.  CH3  •  CO  •  OC2H5, 
ethyl  acetate,  or  by  a  second  acid  radical  with  formation  of  an 
anhydride  ;  the  hydroxyl  may  further  be  replaced  by  halogen, 
especially  chlorine,  to  an  acid  chloride,  by  SH  to  a  thio-aeid, 
by  NH2  to  an  amide,  &c.     (See  Acid  Derivatives,  p.  171.) 

3.  Halogens  act  upon  the  acids  as  substituents  (see  p.  167). 

4.  When  the  alkali  salts  are  heated  with  soda  lime,  or  fre- 
quently when  the  silver  salts  are  heated  alone,  carbon  dioxide  is 
eliminated  and*a  paraffin  formed  (see  e.g.  Methane).  Paraffins  are 
also  formed  when  the  alkali  salts  are  electrolysed  (see  Ethane). 

5.  Most  of  the  acids  are  relatively  stable  towards  oxidizing 
agents,  formic  acid  alone  being  readily  oxidized  to  carbonic 
acid,  and  thus  possessing  strong  reducing  properties. 

6.  When  the  lime  salts  of  the  acids  are  heated  with  calcium 
formate  they  are  reduced  to  aldehydes,  and  when  heated  for 
a  lengthened  period  with  hydriodic  acid  and  phosphorus,  tc 
paraffins. 

Qa.  When  the  lime  salts  are  distilled  alone,  or  are  heated 
with  phosphorus  pentoxide,  they  are  transformed  into  the 
ketones,  (Cn_1H2n_1)2CO. 

Constitution.  —  It  follows  from  their  modes  of  formation, 
especially  3,  4,  and  6,  and  also  from  their  behaviour  (see  4 
above),  that  acetic  acid  and  its  higher  homologues  contain 
alkyl  radicals.  The  conversion  of  the  alcohols  into  acids 
containing  1  atom  of  carbon  more,  by  means  of  the  cyanides, 
is  especially  strong  proof  of  this.  The  latter  contain  the 
alkyl  radical  bound  to  the  nitrile  group  «CiN,  and  when 
they  are  hydrolysed  the  alkyl  radical  remains  unchanged,  and 
the  tervalent  nitrogen  is  replaced  by  0"  and  (OH)',  both  of 
these  attaching  themselves  to  the  carbon  atom  of  the  original 
cyanogen,  and  so  forming  the  group 


(B480) 


146  VI.   MONOBASIC  FATTY  ACIDS 

Consequently  all  the  oxygen  in  the  acid  is  united  to  a  single 
carbon  atom  in  the  form  of  the  group  C02H.  This  group, 
which  is  termed  carboxyl,  is  characteristic  of  the  existence  of 
acid  properties.  Further  proof  of  the  presence  of  the  carboxyl 
group  is  based  largely  on  the  reactions  of  the  acids.  The 
alkyl  group  which  they  contain  must  be  directly  attached  to 
C,  as  it  is  not  removed  by  the  action  of  acids  or  alkalis.  We 
thus  have  CnH?n+1  •  C.  The  presence  of  an  OH  group  follows 
from  the  reaction  of  the  acids  with  PC13  or  PC15,  when  an 
atom  of  0  and  an  atom  of  H  become  replaced  by  an  atom  of 
Cl,  and  they  must  presumably  therefore  be  present  in  the 
form  of  the  univalent  »0«H  group.  There  is  only  1  oxy- 
gen atom  left  over  to  account  for,  and  this  is  presumably 
attached  to  the  C  by  a  double  bond,  and  thus  we  have 

The  monobasic  acids  may  therefore  be  re- 


garded as  compounds  of  the  alkyl  radicals  with  carboxyl,  or, 
in  other  words,  as  derived  from  paraffins  by  the  replacement 
of  one  hydrogen  atom  by  a  carboxyl  group,  thus  :  — 


Formic  acid  is,  in  this  way,  the  hydrogen  compound  of 
carboxyl,  H-COoH. 

The  acids  are  distinguished  as  primary,  secondary,  or  tertiary, 
according  as  the  alkyl  radicals  which  they  contain  are  pri- 
mary, &c.  Thus:  — 

Primary  Secondary  Tertiary 

E-CH2.CO2H         EE'CH.C02H         EE'E"C-C02H. 

There  is  no  room  for  doubt  that  it  is  the  hydrogen  atom  of 
the  carboxyl  group,  the  so-called  "typical"  hydrogen  atom, 
which  is  replaced  by  metals  in  the  formation  of  salts,  for  the 
foregoing  acids  are  all  monobasic,  and  consequently  the  number 
of  hydrogen  atoms  present  in  the  alkyl  radical  is  of  no 
moment  for  the  acid  character.  In  the  di-  and  polybasic 
acids,  the  presence  of  two  or  more  carboxyls  can  usually  be 
demonstrated. 

If  the  composition  of  the  primary  alcohols,  E-CH2'OH,  is 
compared  with  that  of  the  corresponding  acids,  E-CO«OH 
(E  =  alkyl  or  hydrogen),  the  latter  are  seen  to  be  derived 
from  the  former  by  the  exchange  of  two  atoms  of  hydrogen 
for  one  atom  of  oxygen]  The  character  of  the  original 


FORMIC  ACID  147 

substance  is  thus  completely  changed  by  the  entrance  of  the 
electro- negative  (acidifying)  oxygen. 

Nomenclature. — The  names  for  the  first  five  acids  are  special; 
from  C6  onwards,  with  a  few  exceptions,  the  names  for  the 
normal  acids  indicate  the  number  of  carbon  atoms,  e.g.  hexoic, 
heptoic,  or  heptylic,  &c.  The  systematic  name  (Geneva  Con- 
gress) of  the  normal  compound  is  obtained  by  adding  the  word 
acid  to  the  name  of  the  paraffin  containing  the  same  number 
of  carbon  atoms,  e.g.  acetic  acid  =  ethane  acid. 

The  monovalent  radicals  left  when  OH  is  removed  from 
the  molecule  of  each  acid  are  often  spoken  of  as  acid  or 
acyl  radicals.  (Cf.  Alkyl  Eadicals.)  The  commonest  of 
these  radicals  are  CH3»CO.,  acetyl;  C2H5«CO.,  propionyl; 
C3Hr.CO.,  butyryl;  &c. 

The  aldehydes  may  be  looked  upon  as  hydrogen  compounds 
of  the  acyl  radicals,  and  the  ketones  as  compounds  of  the  latter 
with  alkyl  radicals,  thus : — 

(CH3.CO)H  (aldehyde)        (CH3.CO)CH3  (acetone). 

The  constitution  of  aldehydes  and  ketones,  and  of  compounds 
derived  from  them,  is  based  on  the  constitution  of  the  mono- 
basic acids. 

homers. — The  acids  of  the  acetic  series  show  the  same  iso- 
merism  as  the  alcohols  containing  1  atom  of  carbon  less,  since 
they  are  formed  from  these  by  means  of  the  cyanides.  Thus 
we  have  1  propionic  acid,  2  butyric  acids  corresponding  with 
the  2  propyl  alcohols,  4  valeric  acids  corresponding  with  the 
4  butyl  alcohols,  and  so  on. 

Formic  acid  (Methane  acid),  acidum  formidcum,  CH202 
(Samuel  Fisher  and  John  Wray,  1670;  Marggraf),  occurs  free 
in  ants,  especially  Formica  rufa,  in  the  processionary  cater- 
pillar (Bombyx  processionea),  in  the  bristles  of  the  stinging 
nettle,  the  fruit  of  the  soap-tree  (Sapindus  saponaria),  and  in 
tamarinds  and  fir  cones;  also  in  small  quantity  in  various 
organic  liquids,  in  perspiration,  urine,  and  the  juice  of  flesh. 

Formation.— From  HCN,  CHClg,  CH3OH,  C02,  &c.  (See 
General  Methods  of  Formation.)  Its  salts  are  obtained  by 
the  reducing  action  of  sodium  amalgam  upon  ammonium 
carbonate  or  solutions  of  the  alkali  hydrogen  carbonates 
(Lieben);  the  free  acid  by  the  dry  distillation  or  oxidation  of 
many  organic  substances,  e.g.  starch  (Scheele). 

Preparation. — 1.  Sodium  formate  is  obtained  by  absorbing 
carbon  monoxide  in  soda  lime  at  210°  (Merz). 


148  VI.   MONOBASIC  FATTY  ACIDS 

2.  When  oxalic  acid  is  heated,  formic  acid  is  obtained  in 
small  quantity  together  with  carbon  monoxide,  carbon  dioxide, 
and  water,  and  the  same  effect  is  produced  by  the  direct 
action  of  sunlight  upon  its  aqueous  solution  containing  uranic 
oxide  : 

C2H204  =  CO2  +  CH2O2. 

This  decomposition  is  best  effected  by  heating  crystallized 
oxalic  acid  with  glycerol  to  100°-110°  (Berthelot,  Loriri),  the 
formic  acid  produced  combining  with  the  glycerol  to  an  ester, 
monoformin  (see  Glyceryl  Esters)  : 

CH2.OH  CH2.OH 

CH.OH  =    CH-OH          -f  H2O. 


This  remains  behind  in  the  flask,  and  practically  only  water 
and  carbon  dioxide  pass  over.  The  monoformin  is  then  hy- 
drolysed  either  by  boiling  it  with  excess  of  water  or  by  the 
addition  of  more  oxalic  acid,  the  water  of  crystallization  of 
the  latter  acting  as  the  hydrolysing  agent.  The  formic  acid 
distils  over  with  the  water,  and  then  the  anhydrous  oxalic 
reacts  again  with  the  glycerol,  yielding  monoformin  and 
carbon  dioxide,  the  process  repeating  itself  time  after  time, 
a  very  small  amount  of  glycerol  being  thus  sufficient  to 
convert  considerable  quantities  of  oxalic  into  formic  acid. 
(B.  15,  928.)  The  anhydrous  acid  is  obtained  by  decompos- 
ing the  solid  lead  or  copper  salt  with  sulphuretted  hydrogen. 

Properties.  —  It  is  a  colourless  liquid  which  solidifies  in  the 
cold  and  fumes  slightly  in  the  air.  M.-pt.  +9°;  b.-pt.  101°; 
sp.  gr.  .1*22.  It  has  a  pungent  acid  and  ant-like  odour,  acts 
as  a  powerful  corrosive,  and  produces  sores  on  the  soft  parts 
of  the  skin.  It  is  a  much  stronger  acid  than  acetic  acid,  is 
a  powerful  antiseptic,  and  decomposes  completely  into  carbon 
monoxide  and  water  when  heated  with  concentrated  sulphuric 
acid:  CH202  =  CO  +  H20. 

Salts.—  Potassium-,  HC02K,  sodium-,  HC02Na,  and  am- 
monium formate,  HC02NH4,  form  deliquescent  crystals.  The 
first  two  yield  oxalates  when  strongly  heated,  with  evolution 
of  hydrogen  (see  Oxalates);  the  ammonium  salt  yields  form- 
amide  and  water  at  180°: 

HC02.NH4  =  H.C 


ACETIC  ACID  149 

The  lead  salt,  Pb(HC02)2,  forms  glistening,  sparingly  soluble 
needles,  the  copper  salt,  Cu(HC02)2  +  4H20,  large  blue  mono- 
clinic  crystals,  and  _the  silver  salt  colourless  crystals.  The 
last-mentioned  deposits  silver  when  warmed,  consequently  a 
solution  of  nitrate  of  silver  is  reduced  when  heated  with  formic 
acid. 

A  solution  of  the  soluble  mercuric  salt,  Hg(HC02)2,  evolves 
carbon  dioxide  when  gently  warmed,  and  yields  free  formic 
acid  together  with  the  sparingly  soluble  mercurous  salt, 
Hg2(HC02)2,  which  separates  in  white  plates;  on  further 
heating,  carbon  dioxide,  formic  acid,  and  metallic  mercury 
are  obtained.  Similarly  an  aqueous  solution  of  mercuric 
chloride  is  reduced  by  formic  acid  to  the  mercurous  salt, 
Hg2Cl2. 

Formic  acid  is  thus  a  strong  reducing  agent,  and  in  this 
respect  differs  from  the  other  members  of  the  series : 

HCO-OH  ==  C02  +  2H. 

It  decomposes  into  carbonic  acid  and  hydrogen  when  heated 
alone  to  160°,  or  when  brought  into  contact  with  finely-divided 
rhodium. 

This  power  of  reduction  may  be  attributed  to  the  alde- 
hydic  grouping  contained  in  its  constitutional  formula, 
H-O-CHrO. 

Acetic  acid  (Ethane  add),  CH3»COOH,  was  known  in  the 
dilute  form,  as  crude  wine  vinegar,  to  the  ancients.  Stahl 
prepared  the  concentrated  acid  about  1700.  Glauber  mentions 
wood  vinegar  (1648).  Its  constitution  was  established  by 
Berzelius  in  1814.  Salts  of  acetic  acid  are  found  in  various 
plant  juices,  especially  those  of  trees,  and  in  the  perspiration, 
milk,  muscles,  and  excrementa  of  animals.  Esters  of  acetic 
acid  also  occur,  e.g.  triacetin  in  cro ton-oil  (see  p.  158,  and  also 
under  Grlycerol). 

Formation  (see  p.  140  et  seq.).—It,  is  the  final  product  of  the 
oxidation  of  a  great  many  compounds,  and  also  of  their  treat- 
ment with  alkalis. 

The  following  synthesis  is  of  historical  interest: — Perchloro- 
ethylene,  C2C14,  which  is  prepared  from  CC14,  i.e.  from  Cl  and 
CS2,  yields  with  chlorine  in  presence  of  water  in  direct  sun- 
light trichloracetic  acid,  carbon  hexachloride,  C2C16,  being 
obviously  formed  as  intermediate  product  (Kolbe,  1843): 

=  CC13.C02H 


150  VI.   MONOBASIC  FATTY  ACIDS 

The  latter  acid  is  reduced  to  acetic  by  nascent  hydrogen 
(Melsens). 

Preparation. — 1.  From  alcohol. — A  dilute  aqueous  solution 
of  alcohol,  containing  up  to  15  per  cent,  is  slowly  converted 
into  acetic  acid  on  exposure  to  the  oxidizing  action  of  the  air 
and  in  presence  of  certain  low  forms  of  plant  life  known  as 
bacteria,  especially  Bacterium  aceti.  These  organisms  are  con- 
tained in  the  air,  and  hence  become  deposited  in  alcoholic 
liquors  exposed  to  the  air,  and  thus  produce  the  souring  of 
wines,  &c.  For  the  growth  of  the  micro-organisms  it  is 
essential  that  nitrogenous  matter,  phosphates,  &c.,  shall  be 
present,  and  hence  pure  alcohol  mixed  with  water  does  not 
turn  sour.  In  the  "quick  process"  dilute  alcoholic  liquors 
are  allowed  to  trickle  over  beechwood  shavings  which  have 
been  previously  coated  with  the  required  bacteria  (mother  of 
vinegar),  and  the  temperature  is  kept  at  about  35°. 

Vinegar  is  an  aqueous  solution  of  acetic  acid,  usually  con- 
taining only  3  to  5  per  cent,  but  containing  also  small  quan- 
tities of  alcohol,  of  the  higher  acids,  e.g.  tartaric  and  succinic, 
the  ethyl  esters  of  the  acids,  albuminoid  matters,  &c. 

2.  From  wood. — The  dry  distillation  of  wood,  which  is  con- 
ducted in  cast-iron  retorts,  yields:  (1)  gases,  e.g.  hydrogen 
15  per  cent,  methane  11  per  cent,  carbon  dioxide  26  per  cent, 
carbon  monoxide  41  per  cent,  and  higher  hydrocarbons  7  per 
cent;  (2)  an  aqueous  solution  known  as  pyroligneous  acid,  which, 
in  addition  to  acetic  acid,  contains  methyl  alcohol,  acetone, 
homologues  of  acetic  acid,  and  strongly  smelling  combustible 
products  (empyreuma);  and  (3)  wood-tar,  which  contains 
compounds  of  the  nature  of  carbolic  acid.  The  pyroligneous 
acid  is  worked  up  for  acetic  acid  by  converting  it  into  the 
sodium  or  calcium  salt,  heating  these — the  former  up  to  its 
melting-point  and  the  latter  to  200° — to  get  rid  of  empyreu- 
matic  substances,  and  then  distilling  with  sulphuric  acid. 

Properties. — Acetic  acid  is  a  strongly  acid  liquid  of  pungent 
odour,  which  feels  slippery  to  the  touch  and  burns  the  skin, 
and  which  solidifies  on  a  cold  day  to  large  crystalline  plates 
melting  at  17°;  (glacial  acetic  acid).  It  boils  at  118°,  and  its 
vapour  burns  with  a  blue  flame;  sp.  gr.  at  15°,  1*055.  When 
mixed  with  water,  contraction  and  consequent  increase  in  den- 
sity ensue,  the  maximum  point  corresponding  with  the  hydrate 
CH3.C02H  -f  H20,  =  CH3-C(OH)3  (ortho-acetic  acid),  which 
contains  77  per  cent  acid  and  has  a  sp.  gr.  of  1'075  at  15*5°; 
after  this,  the  specific  gravity  decreases  with  further  addition 


ACETATES  161 

of  water,  so  that  a  50-per-cent  acid  has  almost  the  same  density 
as  one  of  100  per  cent.  The  amount  of  acid  present  in  a  solu- 
tion is  determined  either  by  its  sp.  gr.,  this  contraction  being 
borne  in  mind,  or  by  titration  with  standard  alkali,  using 
phenolphthalein  as  indicator,  or  with  very  concentrated  acid 
by  a  careful  determination  of  its  melting-  (freezing-)  point  in 
the  Beckmann  apparatus.  The  vapour  density  near  the  boiling- 
point  is  much  higher  than  that  required  by  theory,  but  is 
normal  above  250°.  The  high  values  are  due  to  the  associa- 
tion of  the  molecules  at  the  lower  temperatures,  and  in  the 
liquid  state  the  molecular  formula  is  undoubtedly  (C2H402)X, 
&c.  The  acid  is  hygroscopic,  and  stable  towards  chromic  acid 
and  cold  permanganate  of  potash.  It  dissolves  phosphorus, 
sulphur,  and  many  organic  compounds,  is  corrosive,  and  gives 
rise  to  painful  wounds  on  tender  parts  of  the  skin. 

Salts. — All  the  normal  acetates  are  soluble  in  water.  The 
following  potassic  salts  are  known : — (a)  KC2H302,  (b)  KC2HS02, 
HC2H302,  and  (c)  KC2H3O2,  2  HC2H302. 

Sodium  acetate,  CH3  •  COONa,  3  H20,  forms  transparent 
readily  soluble  rhombic  prisms.  Ammonium  acetate,  CH3- 
CO  •  ONH4,  resembles  the  potassium  salt.  It  is  used  in  medi- 
cine as  a  sudorific  (liquor  ammonii  acetici).  Its  solution  loses 
ammonia  on  evaporation,  and  it  yields  acetamide  when  dis- 
tilled. Ferrous  acetate,  Fe(C2H302)2,  is  largely  used  in  the 
form  of  "  iron  liquor "  as  a  mordant  in  dyeing.  The  normal 
ferric  salt,  Fe  (C2H302)3,  which  is  employed  for  the  same  pur- 
pose, is  obtained  when  a  soluble  ferric  salt  is  mixed  with  sodium 
acetate.  Its  solution  is  deep  red  in  colour,  and  deposits  the 
iron  as  basic  salt,  CH3  •  CO  •  OFe(OH)2,  when  heated  with 
excess  of  water.  It  is  used  in  medicine  as  "liquor  ferri 
acetici".  The  analogous  aluminic  acetate  is  known  only  in 
solution,  and  finds  a  wide  application  as  "  red  liquor  "  mordant 
in  calico  printing  and  dyeing.  Its  use  depends  upon  the  fact 
that  it  is  readily  hydrolysed  by  water,  e.g.  when  exposed  to  the 
action  of  steam,  and  on  the  insolubility  of  the  compound 
(lake)  formed  from  the  residual  alumina  and  the  colouring 
matter.  It  is  employed  in  small  doses  as  an  astringent  in 
cases  of  diarrhoea,  &c.  Lead  salts.  (1)  Normal  lead  acetate 
or  sugar  of  lead,  (CH3.COO)2Pb  +  3H20,  is  manufactured 
from  sheet-lead  and  acetic  acid.  It  forms  colourless  lustrous 
four-sided  prisms,  which  are  poisonous  and  of  a  ^  nauseous 
sweet  taste.  It  combines  with  lead  oxide  to  (2)  basic  salts  of 
alkaline  reaction,  termed  sub-acetates. 


152  VI.   MONOBASIC  FATTY  ACIDS 

The  simplest  basic  salt  has  the  composition  OH»Pb»0« 
CO-CH3,  but  there  also  exist  others,  e.g.  OH-Pb-O-Pb-p- 
CO-CHg,  &c.  Two  molecules  of  acetic  acid  can  combine 
with  as  many  as  5  molecules  of  lead  oxide.  These  basic 
acetates  are  used  as  Goulard's  lotion,  and  on  the  large  scale 
for  the  preparation  of  white-lead,  &c. 

Cupric  acetate,  Cu(C2H302)2  +  2H20,  dark-green  crystals, 
also  forms  basic  salts  (verdigris).  Silver  acetate,  AgC2H302, 
forms  characteristic  glistening  needles. 

Detection  of  Acetic  Acid. — (1)  When  an  acetate  is  heated  with 
alcohol  and  sulphuric  acid,  the  pleasant-smelling  ethyl  acetate 
is  formed;  (2)  by  means  of  the  silver  salt;  (3)  by  the  odour 
of  cacodyl  produced  upon  heating  the  potassium  or  sodium 
salt  with  arsenious  oxide.  (See  p.  116.) 

Propionic  acid,  CH3.CH2-C02H  (Gottlieb,  1844),  may  be 
obtained  by  the  reduction  of  acrylic  or  lactic  acid  (see  pp. 
143  and  144);  also  from  lactate  or  malate  of  calcium  by  suit- 
able Schizomycetes  fermentation  (Fitz).  It  is  usually  prepared 
by  the  hydrolysis  of  ethyl  cyanide  (propionitrile)  with  alkalis. 
(See  pp.  101  and  142.) 

Calcium  chloride  separates  it  from  its  aqueous  solution  in 
the  form  of  an  oil,  whence  its  name  TT/OWTOS,  the  first,  and  TTIWV, 
fat;  the  first  oily  acid. 

Butyric  acids,  C4H§02. 

1.  Normal  butyric  acid,  butane  add,  ethylacetic  acid, 
CH8  •  CH2  •  CH2  •  C02H,  occurs  free  in  perspiration,  in  the 
juice  of  flesh,  in  the  contents  of  the  large  intestine,  and  in 
the  solid  excrementa;  as  hexyl  ester  in  the  oil  of  the  fruit 
of  Heracleum  giganteum,  as  octyl  ester  in  Pastinaca  sativa,  and 
to  the  extent  of  2  per  cent  as  glyceride  in  butter  (Chevreul, 
1822). 

Formation. — (See  also  General  Modes  of  Formation.)  It 
is  produced  (1)  by  the  decay  of  moist  fibrin  and  of  cheese 
(being  therefore  contained  in  Limburg  cheese);  (2)  by  a  Schizo- 
mycetes fermentation  of  glycerol,  and  of  carbohydrates  (Pelouzc 
and  Gelisj  Fitz;  see  below);  (3)  by  the  oxidation  of  albu- 
minoids with  chromic  acid,  of  fats  with  nitric  acid,  of  coniine, 
&c.,  and  (4)  by  the  dry  distillation  of  wood. 

Preparation. — In  the  "butyric  fermentation"  of  sugar  or 
starch  by  fission  ferments  (e.g.  Bacillus  butyUcus),  CaC03  or 
ZnO  being  added  at  the  same  time,  to  neutralize  the  acid 
formed. 

If  the  fermentation  is  brought  about  by  impure  material 


BUTYRIC  AND  VALERIC  ACIDS  153 

(decaying  cheese,  &c.),  lactic  acid  is  first  produced  by  other 
micro-organisms,  this  being  then  converted  into  butyric  acid 
by  the  butyric  bacillus. 

Properties. — It  is  a  thick  liquid  of  unpleasant  rancid  odour, 
in  presence  of  ammonia  like  that  of  perspiration,  is  miscible 
with  water,  and  separates  from  its  aqueous  solution  on  the 
addition  of  salts.  B.-pt.  163°.  The  calcium  salt,  Ca(C4H702)2 
-f-  H20,  forms  glistening  plates,  and  is  characterized  by  being 
more  soluble  in  cold  than  in  hot  water;  it  therefore  separates 
on  warming  the  concentrated  cold  aqueous  solution.  On  pro- 
longed heating  of  the  solution,  however,  it  is  transformed  into 
the  calcium  salt  of  isobutyric  acid. 

2.  Isobutyric  acid,  2  -  methyl  -  propane  acid,  dimethyl  -  acetic 
acid,  (CH3)2 :  CH  •  C02H,  is  present  in  the  free  state  in  the 
carob  (Redtenbacher),  in  the  root  of  Arnica  montana,  and  as 
esters  in  Pastinaca  saliva  and  Roman  chamomile  oil. 

It  is  obtained  from  isopropyl  cyanide  (Erlenmeyer),  by  the 
oxidation  of  isobutyl  alcohol,  by  the  aceto-acetic  ester  syn- 
thesis (p.  229),  &c.  It  resembles  w-butyric  acid,  but  is  more 
sparingly  soluble  in  water  (1  in  5),  and  boils  9°  lower,  i.e.  at 
154°.  Unlike  the  latter,  however,  it  is  easily  oxidized  to 
acetone  or  acetic  acid,  and  carbonic  acid.  The  calcium  salt, 
Ca(C4H702)2,  differs  from  its  isomer  in  being  more^oluble  in 
hot  water  than  in  cold.  The  solution  is  accompanied  by  a 
slight  absorption  of  heat,  whereas  the  solution  of  the  salt  of 
the  7i-acid  is  accompanied  by  a  slight  evolution  of  heat. 

Valeric  acid,  C5H1002,  exists  in  the  four  different  modifica- 
tions which  are  theoretically  possible: 

1.  Normal  Valeric  acid  (Pentane  acid),  propyl-acetic  acid, 
CH3.(CH2)3.C02H,  from  normal  butyl  cyanide  (Helen  and 
Rossi,  1871),  is  best  prepared  from  propyl-malonic  acid.     (See 
B.  21,  Ref.  649;  also  malonic  ester  synthesis.)    It  boils  at  185°, 
and  is  soluble  in  27  parts  of  water. 

2.  Isovalerio    acid,    3  -methyl  -butane   acid,    isopropyl  -  acetic 
acid,    (CH3)2  :  CH  I  CH2  •  C02H,   is   obtained    from    isobutyl 
cyanide.     It  is  found  in  the  free  state  and  in  the  form  of 
esters  in  the  animal  kingdom  and  in  many  plants,  especially 
(free)  in  the  valerian  root  (Valeriana  officinalis),  and  in  the 
angelica  root  (Angelica  archangelica),  from  which  it  is  obtained 
by  boiling  with  soda;  further,  in  the  blubber  of  the  dolphin 
(Chevreul,  1817),  in   the  berries   of   Viburnum  opulus,  in  the 
perspiration  from  the  foot,  &c.     The  natural  acid  is  usually 
mixed  with  the  active  valeric  acid,  and  is  therefore  optically 


154  VI.   MONOBASIC  FATTY  ACIDS 

active;  the  oxidation  of  fermentation  amyl  alcohol  by  chromic 
acids  yields  a  similar  mixture.  When  pure  it  is  optically  in- 
active, boils  at  175°,  and  has  an  unpleasant  pungent  acid 
odour,  like  that  of  old  cheese,  and  a  corrosive  action.  It  is 
used  in  medicine. 

3.  Methyl  -ethyl  -acetic  acid,  active  valeric  add,  2-  methyl- 

/~1    TT 

butane  acid,   Q  jj3^>CH«C02H,  occurs  in  nature,  as  already 

mentioned,  and  results  from  the  oxidation  of  the  active  (  —  ) 
amyl  alcohol;  it  is  in  this  case  (+)  optically  active,  while, 
if  prepared  synthetically,  e.g.  by  the  aceto-acetic  ester  re- 
action, it  is  optically  inactive,  but  can  be  resolved  by  suitable 
methods  into  a  -j-  valeric  acid  and  a  —  valeric  acid.  [For 
determination  of  optical  activity,  see  section  on  Physical 
Properties.] 

There  are  thus  three  distinct  acids,  one  dextro-rotatory, 
one  Isevo  -  rotatory,  and  the  third  optically  inactive,  which 
have  to  be  represented  by  the  same  structural  formula,  viz.. 


As  regards  their  ordinary  chemical  and  physical  properties, 
the  two  active  acids  are  exactly  alike,  and  differ  only  in  their 
action  on*  polarized  light.  This  difference  is  not  due  to  the 
different  arrangements  of  the  molecules,  as  all  three  are  liquids, 
and  in  liquids  the  molecules  are  not  usually  regarded  as  having 
definite  arrangements.  A  further  proof  that  the  cause  of 
the  activity,  and  hence  of  the  isomerism,  is  to  be  sought  for 
in  the  molecules  themselves,  and  not  in  any  special  arrange- 
ments of  the  molecules,  is  the  fact  that  the  optical  properties 
of  the  acids  in  the  gaseous  state  are  similar  to  those  in  the 
liquid.  The  investigations  of  Pasteur,  Le  Bel,  and  VaiHt  Hoff 
have  shown  that  this  kind  of  isomerism,  which  is  now  usually 
termed  stereo-isomerism,  is  due  to  the  fact  that  the  com- 
pound contains  a  carbon  atom  to  which  4  different  radicals 
are  attached;  in  the  case  of  valeric  acid  these  are,  H,  CH3, 
C2H5,  C02H.  Such  a  carbon  atom  is  usually  termed  an  asym- 
metric carbon  atom.  (This  expression  does  not  mean  that  the 
carbon  atom  itself  is  asymmetric  in  shape,  but  that  it  is  attached 
to  four  distinct  radicals,  and  as  we  shall  see  later  this  pro- 
duces an  asymmetric  molecule.) 

Varit  Hoff  showed  that  if  we  assume  that  these  radicals  are 
arranged  around  the  carbon  atom,  not  in  a  single  plane,  but 
in  the  three  dimensions  of  space,  then  every  compound  con- 


STEREO-ISOMER1SM 


155 


taining  a  single  asymmetric  earbon  atom  should  exist  in  the 
modifications  represented  by  the  figures  1  and  2. 

b  I 


I. 


2. 


Such  modifications  are  not  identical,  since  they  cannot  be 
brought  to  superposition  (this  can  be  shown  readily  by  the 
aid  of  models),  but  they  are  very  similar;  in  fact,  they  stand 
in  the  relationship  of  the  right  to  the  left  hand,  or,  in 
other  words,  in  the  relationship  of  an  asymmetric  object  to 
its  mirror  image. 

The  spatial  relationship  of  the  radicals  is  often  expressed 
by  stating  that  if  the  asymmetric  carbon  atom  is  situated 
as  the  centre  of  a  regular  tetrahedron,  then  the  four  radicals 
occupy  the  solid  angles  of  the  tetrahedron.  The  arguments 
in  favour  of  the  spatial  representation  of  the  molecules  of 
carbon  compounds  are  largely  based  on  a  consideration  of 
the  number  of  isomeric  forms  in  which  simple  carbon  deriva- 
tives occur.  For  example,  no  simple  compound  of  the  type 
Caabb  is  known  to  exist  in  more  than  one  modification. 
If,  however,  the  radicals  and  carbon  atom  were  arranged  in 
a  single  plane,  we  should  expect  the  two  modifications: 

b 


but  with  the  spatial  or  tetrahedral  arrangement  we  can  get 
but  the  one  modification. 

a 


156  VI.   MONOBASIC  FATTY  ACIDS 

An  examination  of  models*  will  clearly  show  that  in  what- 
ever way  we  exchange  the  radicals  a  and  b,  we  always  arrive 
at  a  figure  which  can  be  superimposed  on  the  one  depicted. 

Similarly  with  regard  to  compounds  C  a  a  b  c,  in  which 
2  of  the  4  radicals  are  alike.  The  tetrahedral  arrangement 
allows  of  one  modification  only,  and  in  these  cases  only 
one  is  actually  known.  When,  however,  all  four  radicals  are 
distinct,  e.g.  Cabcd,  the  spatial  arrangement,  as  we  have 
already  seen,  admits  of  two  configurations,  which  are  in  the 
relationship  of  object  to  mirror  image,  and  these  two  modifica- 
tions undoubtedly  represent  the  two  optically  active  isomerides, 
in  which  almost  every  compound  of  the  type  Cabcd  has 
been  shown  to  exist.  An  examination  of  the  models  repre- 
senting the  two  modifications  shows  that  they  are  both  asym- 
metric, i.e.  a  plane  of  symmetry  cannot  be  drawn  through 
them,  and  the  optical  activity  which  such  compounds  exhibit 
when  in  the  liquid  state,  or  in  solution,  is  undoubtedly  con- 
nected with  the  asymmetry  of  their  molecules.  Since  the 
two  configurations  contain  the  same  radicals  and  are  very 
similar,  in  the  one  case  containing  the  4  radicals  arranged 
in  what  we  may  term  a  positive,  and  in  the  other,  in  the 
opposite  or  negative  direction,  we  should  expect  the  molecules 
of  the  two  compounds  to  produce  rotations  of  the  polarized 
ray  equal  in  magnitude  but  of  opposite  sign.  This  is  the  case 
with  the  two  optically  active  valeric  acids:  the  pure  dextro- 
acid  has  a  rotation  of  +  17 '85°,  and  the  laevo-acid  —  17-85°. 

In  addition  to  the  two  optically  active  modifications,  a  third 
isomeride  is  usually  known  which  is  optically  inactive.  As  it 
can  be  synthesised  by  mixing  together  equal  weights  of  the 
d  and  I  compounds,  it  follows  that  such  a  compound  is  either 
a  mixture  or  a  definite  compound  of  the  two  active  isomerides, 
i.e.  its  optical  inactivity  is  owing  to  the  fact  that  the  two 
components  are  present  in  equal  quantities.  Such  isomerides 
are  often  spoken  of  as  racemic  compounds,  and  are  optically 
inactive  by  external  compensation.  Such  racemic  compounds 
may  be  resolved  into  their  optically  active  components  by 

*  In  using  models  it  must  be  remembered  that  the  models  are  not  sup- 
posed to  represent  in  the  least  the  actual  shapes  of  the  atoms,  but  merely 
their  spatial  relationships.  It  must  also  be  borne  in  mind  that  the  atoms 
and  radicals  in  the  molecules  are  in  a  state  of  motion,  and  the  fixed  posi- 
tion represented  in  the  model  may  be  supposed  to  represent  the  mean 
position  of  the  centre  of  gravity  of  any  particular  atom  in  its  oscillatory 
motion,  or  the  position  which  the  centre  of  gravity  would  occupy  at  absolute 
zero. 


HIGHER  FATTY  ACIDS  157 

several  methods,  most  of  which  were  devised  by  Pasteur.  (See 
Kacemic  Acid.) 

Relationship  between  Asymmetry  of  the  Molecule  and  Optical 
Activity. — Since  the  two  isomerides  of  the  type  Cabcd  are 
optically  active,  it  should  follow  that  any  derivative  of  valeric 
acid  in  which  the  four  radicals  attached  to  the  central  carbon 
atom  are  still  different  should  be  also  optically  active,  but 
that  a  derivative  in  which  two  of  the  radicals  become  similar 
should  become  inactive.  This  question  has  been  examined  by 
Le  Bel  in  the  case  of  some  forty  derivatives  of  active  amyl 

C  H  H 

alcohol,  Q  H^^^CH  OH'     ^e  alc°h°l»  its  chloride,  amine, 

all  its  esters,  its  oxidation  product,  viz.  valeric  acid,  and 
all  its  salts,  esters,  &c.,  are  optically  active:  the  hydrocarbon 
C  H  H 

Q  jj^C^CH  °^ta^ne(^  ky  reducing  the  chloride  is,  however,  op- 
tically inactive,  and  cannot  be  resolved  into  active  components. 

4.  Trimethyl-acetie  acid,  pivalic  acid,  (CH3)3C»C02H,  can  be 
prepared  from  tertiary  butyl  cyanide  (Butleroff,  1873).  It  melts 
at  35°,  boils  at  164°,  and  has  an  odour  like  that  of  acetic  acid. 

Of  the  hexylic  acids,  eight  are  theoretically  possible,  and 
of  these  seven  are  already  known.  The  most  important  among 
them  is  normal  caproic  acid,  CH3  •  (CH2)4 -  C02H (Cheweul,  1 822), 
which  is  found  in  nature,  e.g.  in  cocoa-nut  oil,  Limburg  cheese, 
and  as  a  glyceride  in  the  butter  made  from  goats'  milk,  and 
is  produced  in  the  butyric  fermentation  of  sugar,  and  by  the 
oxidation  of  albuminous  compounds  and  of  the  higher  fatty 
acids,  &c.  Like  valeric  acid,  it  has  a  very  unpleasant  and  per- 
sistent odour  of  perspiration  and  rancid  butter.  B.-pt.  205°. 

The  higher  acids  which  are  found  in  nature  are  all  of 
normal  constitution,  and  contain  for  the  most  part  an  even 
number  of  carbon  atoms.  Goats'  butter  contains  the  acids 
C6,  C8,  and  C10,  hence  the  names  caproic,  caprilic,  and  capric 
acids,  and  cocoa-nut  oil — in  addition  to  those  three — the  acid 
C12.  This  last,  lauric  acid,  is  contained  more  especially  in 
oil"  of  laurels  (Laurus  nobilis) ;  myristic  acid,  0^  is  present 
in  oil  of  iris  and  nutmeg  butter  (from  Myristica  moschata); 
arachidic  acid,  C20,  in  the  oil  of  the  earth-nut  (Arachis  hypo- 
gcea);  behenic  acid,  C22,  in  oil  of  ben  (Moringa  oleifera); 
cerotic  acid,  C26,  forms  in  the  free  state  the  chief  constituent 
of  bees'-wax,  and  as  ceryl  ester  that  of  Chinese  wax.  Pal- 
mitic acid,  C16H3202,  and  stearic  acid,  C18H36O2  (pp.  158  and 
161),  are  very  widely  distributed,  being  nearly  always  accom- 


158  VI.   MONOBASIC  FATTY  ACIDS 

panied  by  a  third  acid  poorer  in  hydrogen,  viz.  oleic  acid, 
CjoH^Og  (see  Unsaturated  Acids). 

Most  animal  and  vegetable  fats  and  oils,  e.g.  tallow,  suet, 
butter,  palm,  olive  and  seal  oils,  consist  almost  entirely  of  a 
mixture  of  the  glyceryl  esters  of  palmitic,  stearic,  and  oleic 
acids,  these  esters  being  termed,  for  the  sake  of  brevity, 
palinitin,  C3H5(O.CO.C15H31)3,  stearin,  C3H5(0  •  CO  •  CirH35)3, 
olein,  C3H5(0  •  CO  •  CirH33)3.  Palmitin  and  stearin  being  solid 
and  olein  liquid,  the  consistence  of  a  fat  or  oil  depends  on  the 
preponderance  or  otherwise  of  the  solid  esters.  The  consti- 
tution of  the  fats  was  elucidated  by  Chevreul  in  1811. 

Eancidity  consists,  in  the  case  of  many  fats,  of  a  partial  sa- 
ponification,  whereby  strongly  smelling  fatty  acids  are  set  free. 

Most  of  the  varieties  of  wax  are,  on  the  contrary,  esters  of 
monohydric  alcohols;  thus  bees'-wax  consists  of  the  melissic 
ester  of  palmitic  acid,  C30H610  •  CO  •  C15H31,  together  with  free 
cerotic  acid,  Chinese  wax  (from  Croton  sebiferum,  the  tallow- 
tree)  of  the  ester  C^H^O  •  CO  •  C26H53,  and  spermaceti  (Ceta- 
ceum,  in  the  skull  of  Physiter  macrocephalus)  of  the  ester 
C16H33O.CO.C15H31. 

From  all  these  esters  the  acids  are  obtained  in  the  form  of 
potassium  salts  by  saponification  with  alcoholic  potash,  thus  :  — 


C3H6(O.CO.C17H36)3  +  3KOH  =  3CirHa5C02K  +  C3H6(OH)3 

Stearin  Potassic  stearate  Glycerol. 

The  separation  of  the  acids  is  effected  by  fractional  crystal- 
lization, fractional  precipitation  with  magnesium  acetate,  or  by 
fractional  distillation  either  of  the  fats  themselves  or  of  their 
esters  in  a  vacuum.  Oleic  acid  can  be  separated  from  palmitic 
and  stearic  by  taking  advantage  of  the  solubility  of  its  lead 
salt  in  ether. 

The  stearine  candles  of  commerce  consist  of  a  mixture  of 
palmitic  with  excess  of  stearic  acid,  some  paraffin  or  wax  being 
usually  added  to  prevent  them  becoming  crystalline.  The 
manufacture  of  candles  depends  upon  the  saponification  of  the 
solid  fats,  especially  of  beef  and  mutton  tallow,  by  means  of 
water  and  lime,  of  concentrated  sulphuric  acid,  or  of  super- 
heated steam. 

Soaps  consist  of  the  alkaline  salts  of  palmitic,  stearic,  and 
oleic  acids,  hard  soaps  containing  sodic  salts,  chiefly  of  the  solid 
acids,  while  soft  soaps  contain  potassic  salts,  principally  oleate. 
By  the  addition  of  common  salt  to  a  solution  of  a  potassic  soap, 
the  latter  is  converted  into  a  sodic  soap,  which  is  insoluble  in 


SOAPS  159 

a  solution  of  sodic  chloride.  This  process  is  usually  termed 
"salting  out",  and  is  analogous  to  the  precipitation  of  sodic 
chloride  by  the  addition  of  hydric  chloride  to  its  saturated 
solution.  (Cf.  Walker,  "Phys.  Chem.",  p.  314.)  These  alkali 
soaps  dissolve  to  a  clear  solution  in  a  little  water,  but  with 
excess  of  water  are  hydrolysed  to  a  certain  extent,  yielding 
free  alkali  and  free  fatty  acid  or  acid  salt,  analogous  to  potassic 
peracetate.  The  cleansing  action  of  soap  is  usually  attributed 
to  the  presence  of  the  small  amount  of  free  alkali  thus  formed  : 

+  NaOH. 


This  hydrolysis  is  similar  to  that  observed  in  the  case  of 
inorganic  salts  derived  from  a  feeble  acid  and  a  strong  base, 
and  increases  with  increasing  dilution.  The  production  of 
free  alkali  (or  free  hydroxyl  ions)  can  be  readily  understood 
by  aid  of  the  theory  of  ionization.  The  salt  R»C02Na,  when 
dissolved  in  water,  may  be  assumed  to  be  ionized  to  a  certain 

extent  in  the  normal  manner,  thus  giving  rise  to  cations  Na 

and  anions  R»C02.     But  water  itself  is  ionized  to  a  slight 

+  + 

extent  to  H  and  OH  ions,  and  we  should  thus  have  H  and 

R»C02  ions  in  the  same  solution;  the  acid  from  which  the 
sodic  salt  is  derived  is  a  feeble  acid,  and  hence  shows  little 

tendency  to  ionize,  and  thus  the  H  and  R'C02  ions  will  unite 
to  form  non-ionized  molecules  R«C02H.  This  implies  removal 
of  hydrions  from  the  sphere  of  chemical  action,  and  a  certain 
number  of  water  molecules  will  be  ionized  in  order  to  supply 
fresh  hydrions  ;  these  will  again  unite  with  the  acid  ions,  and 
the  two  reactions  will  proceed  until  a  state  of  equilibrium 
is  established.  In  this  state  of  equilibrium  we  shall  have 

R.C02,  Na,  H,  OH  ions  and  R-C02H  and  H20  molecules; 
but  it  is  obvious  that  the  OH  ions  will  be  largely  in  excess  of 

the  H  ions,  since  a  considerable  number  of  these  latter  have 
been  used  up  in  forming  non-ionized  molecules  of  acid.  The 
solution,  as  a  whole,  will  thus  possess  more  or  less  pronounced 
alkaline  properties.  (Cf.  Walker,  "Phys.  Chem.",  p.  290.) 
The  calcium,  barium,  and  magnesium  salts  are  insoluble  in 
water,  but  partly  crystallizable  from  alcohol.  The  preci- 
pitates produced  by  the  action  of  hard  waters  on  soaps  consist 


160  VI.   MONOBASIC  FATTY  ACIDS 

largely  of  those  insoluble  salts.  The  lead  salts  are  prepared 
by  boiling  fats  with  lead  oxide  and  water,  and  form  the  so- 
called  plaisters  or  lead  plaisters. 

The  higher  acids  with  an  uneven  number  of  carbon  atoms, 
Cn,  C13,  C15,  and  C17,  are  prepared  synthetically  from  the  acids 
containing  1  atom  of  carbon  more,  by  transforming  them  into 
the  ketones  C^H^^CO'CHa  (p.  131),  and  oxidizing  these, 
when  acids  Cn_2H2n_3 •  COOH  are  obtained.  (Krafft.) 

On  these  reactions  a  method  for  proving  that  the  higher 
fatty  acids,  e.g.  palmitic  and  stearic,  are  normal  in  constitution 
has  been  based.  (See  Caution,  p.  132.) 

The  acid  C15H31  •  C02H  is  converted  into  the  ketone  C15H31  • 
CO«CH3;  this  on  oxidation  yields  C14H29»C02H  and  acetic  acid. 
The  conversion  into  ketone  and  subsequent  oxidation  is  re- 
peated, and  an  acid,  C13H27-C02H,  obtained.  The  processes 
are  repeated  until  an  acid,  CH3  •  (CH2)7  •  C02H,  ?i-nonylic  acid, 
is  obtained.  This  can  be  shown  to  have  a  normal  structure 
by  synthetical  methods,  and  hence  all  the  higher  acids  must 
also  have  a  normal  structure,  since  if  the  acid  C13H2lr'C02H 
had  not  a  normal  structure,  but  contained  a  side  chain,  e.g. 

Q  jj  3^>CH«C02H,  on  conversion  into  the  ketone  and  sub- 
sequent oxidation  it  would  not  yield  the  acid,  C12H25-C02H, 
but  a  ketone,  CH3  •  CO  •  CnH23,  or  the  oxidation  products  of 
this  ketone. 

Dissociation  constant.  —  One  of  the  most  characteristic 
physical  constants  of  the  organic  acids  is  what  is  termed  the 
dissociation  or  affinity  constant  K,  which  is  derived  from 

the    equation   k   =    — -, =,  where  v  =  volume  of  solution 

v  (1  —  a) 

in  litres  containing  1  gram  mol.  of  the  acid,  a  is  the  amount 
ionized,  and  1  —  a  the  amount  not  ionized.  This  equation  is 
based  on  the  law  of  mass  action.  In  the  case  of  any  feeble 
organic  acid,  e.g.  acetic  acid,  where  we  have  1  gram  molecule 
dissolved  in  v  litres  of  solution,  a  state  of  equilibrium  repre- 
sented by  the  equation  + 
CH3.COOH  ^  CH3"COO  +  H 

occurs.  Then  if  ^  and  Jc2  represent  the  velocity  constants  of 
the  direct  and  reverse  reactions,  we  have,  according  to  Guld- 
berg  and  Waage's  law,  at  the  stage  of  equilibrium: — 

*,  X  !^  =  k  X  ?  X  «      or          «^       =  |»  =  *• 

v  v       v  v(l  —  a}        £ 


UNSATURATED   ACIDS 


161 


The  extent  of  ionization  in  a  solution  containing  1  grain 
molecule  in  v  litres  is  determined  by  electrical  conductivity 

determinations,     a  =    — ,  i.e.  the  degree  of  ionization  at  a 

dilution  v  is  the  ratio  of  the  molecular  conductivity  at  this 
dilution  to  the  molecular  conductivity  at  infinite  dilution 
when  all  the  acid  molecules  are  ionized.  (Cf.  Walker,  pp. 
232-235.)  For  a  weak  acid,  k  remains  constant,  and  affords 
a  convenient  measure  of  the  strength  of  an  organic  acid. 
As  a  rule,  the  constant  is  usually  taken  as  100  times  k,  or  K 
=  100  k. 


Acid. 


K. 


Formic.          Acetic.         Propionic.     7i-Butyric.    iso-Butyric. 
0-0214       0-00180       0-00134      0'0015       0'00144 


Formic  acid  is  obviously  much  the  strongest  of  the  fatty 
acids,  but  they  are  all  comparatively  weak  acids  compared 
with  the  strong  mineral  acids.  Close  comparison  cannot  be 

a? 
drawn  between  the  two  groups,  as  the  equation  k  =  n__a\v 

does  not  hold  good  for  strong  acids. 

Palmitic  acid  (hexadecane  acid),  CH3'(CH2)14.C02II,  is  most 
conveniently  prepared  from  palm-oil,  which  is  a  mixture  of 
palmitin  and  olein;  also  by  fusing  oleic  acid  or  cetyl  alcohol 
with  potash.  M.-pt.  60°. 

Stearic  acid,  CH3.(CH?)16'C02H,  is  formed,  among  other 
methods,  by  reducing  oleic  acid,  and  is  also  obtained  from 
the  so-called  shea-butter  or  from  mutton  suet.  M.-pt.  68°. 
"Artificial  ivory"  consists  of  gypsum  which  has  been  saturated 
with  liquid  stearic  acid. 

B.  Unsaturated  Acids,  CuH2n_A  or  CJL 


Melting-pt. 

Boiling-pt, 

Acrylic  acid  CoH^Oo 

7° 

140° 

(la 

72° 

182° 

Crotonic  acids,  C4H6O2 

Jib 

Li 

15° 
16° 

172° 
160° 

Angelic  acidl  n  TT  n 
Tiglicacid    )G5H8°2- 

45° 
65° 

185° 
198° 

Olpir*  arirt    (7    hi    ()> 

14 

•  •  • 

Erucic  acid  CXofJ^O?  . 

33° 

•  •• 

( B  480  ) 


162  VI.   MONOBASIC  FATTY  ACIDS 

These  acids  are  known  as  the  acids  of  the  oleic  series.  In 
their  physical  properties  they  closely  resemble  the  saturated 
acids,  apart  from  differences  in  melting-point,  which  are  some- 
times considerable.  They  have  the  chemical  properties  char- 
acteristic of  monobasic  acids;  they  yield  salts,  esters,  amides, 
&c.,  in  much  the  same  manner  as  the  saturated  acids;  but  in 
addition  they  resemble  the  olefines  in  the  readiness  with 
which  they  yield  additive  compounds  with  hydrogen,  halo- 
gens, or  halogen  hydrides,  thus  forming  fatty  acids  or  their 
substitution  derivatives.  Thus  oleic  acid,  C18H3402,  when 
treated  with  H2  in  presence  of  colloidal  Pd,  yields  steanc 
acid,  C18H3602,  and  with  bromine,  dibromo  -  stearic  acid, 
C18H34Br202.  In  this  way  they  characterize  themselves  as 
derivatives  of  the  unsaturated  hydrocarbons  of  the  ethylene 
series,  from  which  we  may  imagine  them  to  be  formed  by  the 
replacement  of  an  atom  of  hydrogen  by  carboxyl.  They  may 
therefore  be  termed  olefine-carboxylic  acids. 

Upon  the  addition  of  halogen  hydride,  the  halogen  does  not 
always  attach  itself  to  that  carbon  atom  to  which  the  smaller 
number  of  hydrogen  atoms  is  united. 

The  presence  of  the  double  bonds  renders  them  much  more 
sensitive  to  oxidizing  agents  than  are  the  fatty  acids.  When 
a  very  dilute  oxidizing  agent  is  employed,  e.g.  1  per  cent 
permanganate,  dihydroxy  derivatives  of  fatty  acids  are  ob- 
tained : 

CH3.CH:CH.C02H  +  0  +  H20  =  CH3.CH(OH).CH(OH).CO2H; 

but  if  stronger  oxidizing  agents  are  employed,  a  rupture  of 
the  molecule  occurs  at  the  position  where  the  double  bond 
exists,  and  a  mixture  of  acids  is  obtained: 

CH3  •  CH :  CH  •  CH2 .  CO2H  —  CH3  •  CO2H  and  C02H  •  CH2  •  CO2H. 

This  affords  an  excellent  method  for  determining  the  position 
of  the  double  bond  in  the  molecule  of  the  acid.  Fusion  with 
caustic  alkalis  also  causes  a  breaking  up  of  the  molecules,  and 
the  formation  of  a  mixture  of  fatty  acids;  but  this  reaction  is 
of  no  use  for  determining  the  position  of  the  double  bond,  as 
treatment  with  alkali  tends  to  shift  the  double  bond,  if  possible, 
nearer  to  the  carboxylic  group.  Fittig  (B.  1891,  24,  82,  &c.) 
has  studied  the  action  of  dilute  alkalis  on  a  number  of  un- 
saturated acids,  and  always  observed  the  same  effect,  e.g. 
bydrosorbic  aci4,  CH3  •  CH2  •  CH :  CH  •  CH2  •  COOH,  passes  into 


FORMATION   OF  UNSATURATED  ACIDS  163 

OH3  •  CH2 .  CH2  •  CH :  CH .  COOH  (2  -  hexene  - 1  -  add).  Such 
changes,  which  are  termed  "  molecular  transformations  ",  are 
sxplained  by  the  assumption  that  atoms  or  radicals  (in  this 
sase  the  elements  of  water)  are  added  on  to  the  original 
compound,  and  then  eliminated  in  a  different  manner,  e.g. : 

CH3.CH:CH.CH2.CO2H  —  GHo.CH2.CH(OH).CH2.C09H 
->  CH3.CH2.CH:CH.C02H. 

The  presence  of  the  double  bond  in  the  molecule  has  a  con- 
siderable effect  upon  certain  properties  of  the  acid;  for  ex- 
ample, the  dissociation  constant  and  the  rate  of  esterification 
)y  the  catalytic  method. 

Fichter  and  Pfister  have  shown  (Abs.  1904,  i.  965)  that  the 
ntroduction  of  a  double  bond  usually  increases  the  strength  of 
an  acid,  and  that  the  effect  is  most  marked  when  the  double 
xmd  is  in  the  /2-y-position,  e.g.  butyric  acid,  K  =  0 '00 154;  cro- 
;onic  acid,  K  =  0-00204;  and  for  vinyl  acetic,  K  =  0-00383. 

Sudborough  (J.  C.  S.  1905,  1840;  1907,  1033;  1909,  315, 
975)  has  shown  that  the  introduction  of  the  double  bond  in 
the  a-position  greatly  retards  esterification.  The  rates  for 
hydrocinnamic,  C6H5  •  GEL  •  CH2  •  C02H,  and  for  cinnamic  acid, 

6H6.CH:CH.C02H,  are  as  40:1. 

Modes  of  Formation. — 1.  By  oxidizing  the  corresponding 
Icohols  or  aldehydes,  e.g.  acrylic  acid  from  allyl  alcohol  or 
acrolein. 

CH2:CH-CH2.OH  —  CH2:CH-CHO  ->  CH2:CH.C02H. 

2.  From  the  unsaturated  alcohols  or  their  iodides,  by  con- 
verting them  into  nitriles  and  hydrolysing  these,  e.g.  crotonic 
acid  from  allyl  iodide  (intramolecular  rearrangement,  p.  164). 

CH2:CH.CH2I  —  CH3.CH:CH.CN  —  CH3-CH:CH.CO2H. 

Both  these  methods  of  formation  are  analogous  to  those  of 
.he  fatty  acids. 

3.  From  the  monohalogen  substitution  products  of  the  satu- 
rated fatty  acids,  by  warming  with  alcoholic  potash,  sometimes 
upon   simply   heating  with   water.     This   reaction  is  analo- 
gous to  the  formation  of  the  olefines  from  alkyl  haloids ;  it 
occurs  in  the  case  of  those  substituted  acids  which  contain 
the  halogen  in  the  ^-position  to  the  carboxyl  (see  p.  167 


164  VI.   MONOBASIC  FATTY  ACIDS 

4.  From  the  halogen  substitution  products  of  the  unsati 
rated  acids  by  inverse  substitution: 

CH3.CH:CC1.CO2H  —  CH3.CH:CH.C02H. 

5.  By  the  elimination  of  water  from  hydroxy  fatty  acids. 

CH2(OH).CH2.COOH  =  CH2:CH.(X)2H  +  H2O 

Ethylene-lactic  acid  Acrylic  acid. 

This  reaction  corresponds  with  the  formation  of  the  olefine 
from  monohydric  alcohols. 

Constitution  and  homers.  —  The  constitution  of  the  unsaturate< 
acids,  CnH2n_2O2,  follows  from  their  behaviour  as  monobasi 
acids  and  as  unsaturated  compounds,  and  the  position  of  th 
double  bond  is  ascertained  by  the  process  of  oxidation.  Th 
number  of  isomeric  acids,  CmK<im_i  •  C02H,  is  the  same  as  th 
number  of  isomeric  unsaturated  alcohols,  C^H^^-OH. 

Acrylic  acid,  propene  acid,  ethylene-carboxylic  acid,  CH2:CH 
C02H  (Redtenbacher),  is  prepared  by  the  oxidation  of  acrolei 
by  oxide  of  silver,  or  by  the  distillation  of  /3-iodopropioni 
acid  with  oxide  of  lead.  (Cf.  mode  of  formation  3.)  It  i 
very  similar  to  propionic  acid.  Mixes  with  water  and  readil 
polymerizes.  It  is  reduced  to  propionic  acid  when  warmei 
with  zinc  and  sulphuric  acid,  and  is  decomposed  when  fuse< 
with  alkali  into  acetic  and  formic  acids. 

Acids,  C4H602.  Four  isomeric  acids  with  this  formula  ar 
known.  1.  Ordinary  or  solid  crotonic  acid  (2-Buten-l-acid] 
CH3  •  CH  :  CH  •  C02H,  occurs  along  with  isocrotonic  aci< 
in  crude  pyroligneous  acid,  and  is  prepared  from  allyl  iodid 
by  means  of  the  cyanide,  which,  instead  of  having  the  antici 
pated  formula,  CH2  :  CH  •  CH2  •  CN,  has  the  isomeric  one 
CH3'CH:CH»CN;  this  affords  another  example  of  molecula 
transformation. 

It  is  also  prepared  by  heating  malonic  acid  with  para 
aldehyde  and  glacial  acetic  acid: 


It  crystallizes  in  large  prisms,  melts  at  72°,  boils  at  189°,  ha 
an  odour  like  that  of  butyric  acid,  and  is  fairly  soluble  ii 
water.  On  reduction  it  yields  ?i-butyric  acid,  and  on  carefu 
oxidation,  oxalic  acid,  hence  the  constitution. 

2.  Isocrotonic  acid,  CH3-CH:CH.C02H,  obtained  by  tin 


OLEIG  AClt>  165 

tction  of  sodium  amalgam  upon  chloro-isocrotonic  acid,  melts 
it  15°,  boils  .at  172°,  and  changes  into  ordinary  crotonic  acid 
it  180°.  It  is  present  in  croton-oiL  For  preparation  of  the 
mre  acid  see  Morrell  and  Cellars,  J.  C.  S.  1904,  345. 

Isocrotonic  acid  was  formerly  regarded  as  CH2:CH«CH2« 
}02H,  but  it  shows  almost  the  same  chemical  behaviour  as 
3rotonic  acid,  e.g.  on  reduction  and  oxidation,  or  on  addition 
)f  hydrogen  bromide,  and  is  now  regarded  as  having  the  same 
.tructural  formula  as,  but  being  stereo-isomeric  with,  solid 
TO  tonic  acid.  (Cf.  Fumaric  and  Maleic  acids.) 

3.  Meth-acrylic  acid,  2-methyl-2-propene-l-actd,  CH2 :  C<^QQ  Vr, 

s  found  in  small  quantity  in  Eoman  chamomile  oil,  and  may 
be  obtained  by  the  withdrawal  of  HBr  from  bromo-isobutyr.c 
icid: 


t  smells  like  decaying  mushrooms,  and  melts  at  15°. 

4.  Vinyl-acetic  acid,  CH2 :  CH .  CH2  •  C02H,  1-ButeneA-acid., 
nay  be  obtained  synthetically. 

Angelic  acid,  CH3  •  CH :  C(CH3)C02H,  is  present  in  the  an- 
gelica root,  and,  together  with  its  stereo-isomer,  tiglic  acid,  in 
.ioman  chamomile  oil.  (Cf.  A.  250;  259,  24;  272,  1;  273,  127.) 
PIC  relationship  of  these  two  acids  is  exactly  the  same  as  that 
of  crotonic  and  isocrotonic  acids. 

Oleic  acid,  C18H3402  (Chevreul),  is  present  as  olein  (glyceryl 
oleate)  in  the  fatty  oils  especially,  e.g.  olive,  almond,  and  train 
oils.  It  is  a  colourless  oil,  solidifies  to  white  needles  in  the 
cold,  melts  at  14°,  and  cannot  be  volatilized  without  decom- 
position. It  is  tasteless  and  odourless,  and  has  no  action 
upon  litmus,  but  quickly  becomes  yellow  and  acid  by  oxi- 
dation in  the  air,  and  also  acquires  a  rancid  odour.  Its  lead 
salt  is  soluble  in  ether,  and  by  this  means  the  acid  ^  may  be 
separated  from  numerous  other  organic  acids.  It  yields,  on 
fusion  with  potash,  the  saturated  acids,  palmitic  and  acetic. 
Nitrous  acid  converts  it  into  the  stereo-isomeric  crystalline 
elai'dic  acid,  melting  at  45°.  It  contains  a  normal  chain, 
since  on  reduction  it  yields  stearic  acid.  When  carefully 
oxidized,  it  yields  pelargonic  acid,  CH3  •  (CH2)7  •  C02H,  and 
azelaic  acid,  C02H.(CH2)7-C02H,  and  hence  the  constitu- 
tional  formula: 

CH3.(CH2)7-CH:CH.(CHo)7.C02H. 


166  VI.   MONOBASIC  FATTY  ACIDS 

Erucic  acid,  C22H4202,  occurs  in  rape-seed  oil,  melts  at  33' 
and  on  treatment"  with  nitrous  acid  yields  the  stereo-isomeri 
brassidic  acid,  melting  at  60°.  The  constitution  is  probably : 

CH3[CH2]7  •  CH :  CH[CH2]n  •  CO2H. 

iFor  the  stereo-chemistry  of  the  unsaturated  acids,  see  Fumari 
<and  Maleic  acids. 


C.  Propiolic  Acid  Series,  CnH2u_/>2 

The  acids  of  this  series  again  contain  two  atoms  of  hydroge; 
less  than  those  of  the  former,  and  are  to  be  regarded  as  cai 
boxylic  acids  of  the  acetylene  hydrocarbons,  e.g.  propiolic  acid 
CH:C«C02H,  as  acetylene-carboxylic  acid.  They  can  ac 
cordingly  be  prepared  by  the  addition  of  C02  to  the  sodiur 
derivatives  of  the  acetylenes  (analogously  to  mode  of  formatioi 
4  of  the  saturated  acids,  p.  143). 

They  closely  resemble  the  unsaturated  acids  which  have  beei 
already  described,  but  differ  from  them  by  the  fact  that  eac" 
molecule  of  such  an  acid  can  combine  with  either  2  or  4  atom 
of  hydrogen,  chlorine,  bromine,  &c.,  and  can  yield  explosiv 
compounds  with  ammoniacal  silver  and  copper  solutions 
There  are,  however,  acids  of  the  formula  CnH2n_402  which  d 
not  possess  this  last  peculiarity,  viz.,  those  which  are  derived 
not  from  the  homologues  of  acetylene  proper,  but  from  thei 
isomers,  and  which  therefore  contain  two  double  bonds  instea* 
of  a  triple  one.  (Compare  Acetylene  Hydrocarbons,  p.  51.) 

The  most  important  member  of  the  series  is  propiolic  o 
propargylic  acid,  pi-opine  add,  CH:C-C02H,  which  corn 
sponds  with  propargyl  alcohol,  and  is  prepared  by  warmin 
an  aqueous  solution  of  the  acid  potassium  salt  of  acetylene-d 
carboxylic  acid,  the  latter  being  itself  obtained  from  dibronu 
succinic  acid.  (See  p.  241,  also  B.  18,  677.)  In  its  physic* 
properties  it  resembles  propionic  acid,  forms  silky  crystal 
below  6°,  and  boils  at  144°.  It  is  readily  soluble  in  wate 
and  alcohol,  and  becomes  brown  in  the  air.  It  gives,  even  i 
dilute  solution,  the  characteristic  explosive  silver  precipitate, 

Tetrolic  acid,  CH3'C:C-C02H,  is  obtained  from  /3-chlor< 
crotonic  acid  and  aqueous  potash,  and  melts  at  76°. 

Sorbic  acid,  CH3.CH:CH.CH:CH.C02H,  is  contained  i 
the  juice  of  the  unripe  sorb  apple  (Sorbus  Aucuparia),  and  ha 
relatively  high  melting-  and  boiling-points. 


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167 


168  VI.   MONOBASIC  FATTY  ACIDS 

The  acids  poorer  in  hydrogen  also  yield  similar  substitution 
products,  e.g.  CH2 : CC1  •  C02H,  a-chlor-acrylic  acid;  CHBr: 
CH.C02H,  £-brom-acrylic  acid;  CH3 - CH : CC1  •  C02H,  a-chlor- 
crotonic  acid;  CI:C»C02H,  iodo-propiolic  acid,  &c. 

All  these  halogen  derivatires  have  the  properties  of  mono- 
basic acids;  in  many  respects  they  resemble  the  parent  sub-- 
stances,  but  as  a  rule  are  much  stronger  acids.  This  is  ex-* 
tremely  well  shown  in  a  comparison  of  the  dissociation  con- 
stants K.  (See  table.) 

Since  their  acid  nature  remains  unaltered,  they  still  contain 
the  carboxyl  group;  the  halogen  has  therefore  replaced  the 
hydrogen  of  the  hydrocarbon  radical.  They  may  also  be 
looked  upon  as  haloid  substitution  products  of  the  hydro- 
carbons, in  which  1  atom  of  hydrogen  is  replaced  by  carboxyl : 

CH3C1  (chloro-methane)        CH2C1  •  C02H  (chlor-acetic  acid). 

The  modes  of  formation  and  properties  of  these  substituted 
acids  also  coincide  with  this  view.  Tkus,  while  they  show  a 
behaviour  perfectly  analogous  to  that  of  the  non-substituted 
acids,  forming  salts,  esters,  chlorides,  anhydrides,  and  amides, 
their  halogen  atoms  are  as  readily  exchangeable  for  OH,  CN, 
or  S03H,  as  are  those  of  the  substitution  products  of  the 
hydrocarbons.  (See  p.  61.) 

homers  and  Constitution. — While  in  each  case  only  one  mono-, 
di-,  &c.,  halide  acetic  acid  exists,  two  isomeric  monohaloid 
propioni'c  acids  are  known.  This  is  readily  explicable  from 
the  fact  that  in  propionic  acid,  CH3  •  CH2  •  C02H,  the  two  a-hy- 

/3  a 

drogen  atoms  are  differently  situated  from  the  three  /?-  ones, 
the  former  being  attached  to  the  carbon  atom  nearer  to  the 
carboxyl,  and  the  latter  to  that  one  farther  from  it.  According 
to  theory,  therefore,  with  which  the  observed  facts  agree,  the 
following  two  isomers  are  possible : — 

CH3.CHX.C02H    and    CH2X.CH2-C02H 

a-Haloid-propionic  acid  jS-Haloid-propionic  acid. 

These  acids  yield  two  isomeric  lactic  acids  by  exchange  of 
their  halogen  for  hydroxyl,  thus : — 

GH3.CH(OH).C02H    and    CH2(OH).CH2.CO2H 
Common  lactic  acid  Ethylene-lactic  acid. 

The  constitution  of  both  of  these  lactic  acids  follows  from 
their  other  modes  of  formation  (see  p.  207,  et  seq.).  The 


FORMATION  OF  HALOID  FATTY  ACIDS  169 

positions  of  the  halogens  in  the  a-  and  ft-  substituted  propionic 
acids  are  thus  also  fixed. 

Those  substituted  acids  which  contain  the  halogen  attached 
to  the  a-carbon  atom,  i.e.  to  the  same  carbon  atom  to  which 
the  carboxyl  group  is  united,  are  termed  a-acids,  and  the  others 
/?,  y,  &c.,  acids,  the  successive  carbon  atoms  in  their  order 
from  the  carboxyl  group  being  designated  as  a,  /?,  y,  &c. 

We  thus  distinguish,  for  instance,  between  a-,  /3-,  and  y- 
chloro-butyric  acids,  aa-,  aft-,  and  fifi-  dibromo-propionic  acids, 
&c. 

Two  stereo-isomeric  forms  of  the  a-  or  /?-  mono-chloro-  and 
-bromo-crotonic  acids  are  known  (A.  248,  281),  being  derived 
from  crotonic  and  isocrotonic  acids  respectively. 

Formation.  —  (a)  Of  the  saturated  substituted  acids. 

1.  Chlorine  and  bromine  can  substitute  directly,  the  halogen 
taking  up  the  a-position  to  the  carboxyl. 

The  reaction  is  often  carried  out  in  sunlight  and  in  the 
presence  of  a  halogen  carrier.  One  of  the  commonest  methods 
is  to  transform  the  acid  into  the  acid  bromide  by  the  aid  of 
phosphorus  and  bromine,  and  then  to  brominate.  The  pro- 
duct obtained,  e.g.  CH3  •  CHBr  •  COBr,  on  treatment  with  water 
yields  the  a-bromo  acid,  CH3»CHBr.C02H.  This  is  generally 
known  as  the  Hell-VoUmrd-Zelinsky  method.  Trimethyl  acetic 
acid,  CMe3»C09H,  which  contains  no  a-hydrogen  atom,  cannot 
be  brominated  in  this  manner  (B.  1890,  23,  1594). 

2.  From  hydroxy  acids  of  the  gly  collie  series  by  the  action 
of  PC15,  HBr,  &c.,  e.g.  : 

CH3.CH2.CH(OH).CO2H  ->  CH3.CH2.CHC1.C02H. 

3.  By  the  addition  of  halogen  or  halogen  hydride  to  the 
unsaturated  acids. 

(b)  Of  the  unsaturated  substituted  acids.  These  are  often 
prepared  by  the  elimination  of  HC1,  HBr,  or  HI  from  poly- 
halogen  derivatives  of  the  fatty  acids: 

CH3-  CHBr-  CHBr-  CO2H  ->  CHs-C 


or  by  the  addition  of  hydrogen  halide  to  propiolic  acids. 

Behaviour.  —  1.  For  the  replacement  of  chlorine,  bromine, 
and  iodine  by  hydroxyl,  see  p.  206.  This  exchange  takes 
place  with  more  difficulty  in  the  a-monochloro-substituted 
acids  than  in  the  corresponding  bromine  and  iodine  com- 
pounds, but  more  easily  than  in  the  case  of  the  alkyl 
chlorides,  and  it  is  effected  by  means  of  moist  silver  oxide, 


170  VI.   MONOBASIC  FATTY  ACIDS 

or  frequently  by  prolonged  boiling  with  water  alone  (A.  200, 
75).     In  this  way  monochlor-acetic  yields  glycollic  acid: 

CH2C1.C02H  +  H2O  =  OH.<JE2.CO2H 


/2-halogen  acids,  on  the  other  hand,  lose  halogen  hydride 
when  boiled  with  water,  and  yield  unsaturated  acids,  together 
with  C02  and  olefines  Cn_1H2n_2.  y-halogen  acids  break  up 
under  these  conditions  (even  with  cold  soda  solution)  into 
HC1,  &c.,  and  a  lactone,  i.e.  an  anhydride  of  a  y-hydroxy-acid 
(see  p.  217;  cf.  Fittig,  A.  208,  116). 

2.  When   boiled  with  an  alcoholic  solution   of   potassium 
cyanide,  cyano-fatty  acids  are  produced: 
CH2C1.C02K 


These  compounds  are  on  the  one  hand  monobasic  acids, 
and  on  the  other  nitriles,  and  they  consequently  yield  dibasic 
acids  when  hydrolysed.  In  the  above  case  malonic  acid, 
C02H.CH2.C02H,  is  formed. 

3.  They  form  sulphonic  acids  with  sodium  sulphite,  e.g.  : 

CH2a.C02Na  +  Na.S03Na  =  NaSOj-GHj-OOjNa  +  NaCl. 


These  latter  are  compounds  which,  apart  from  the  acid 
character  they  derive  from  the  carboxyl  group,  are  actual  sul- 
phonic acids,  like  ethyl-sulphonic  acid,  and  are  thus  dibasic. 
Their  sulpho-group  can,  however,  be  replaced  by  OH  on  boiling 
with  alkalis. 

4.  With  AgN02,  under  favourable  conditions,  nitro-deriva- 
tives  of  the  fatty  acids  are  formed,  and  these  yield  amino- 
acids  on  reduction,  e.g.  NH2  -  CH2  •  C02H.  (B.  1910,43,3239.) 

Chloroformic  acid,  Cl  •  C02H,  has  so  far  not  been  prepared, 
although  derivatives  of  it  are  known.  (Cf.  Chloro-carbonic 
acid.) 

The  chlorinated  acetic  acids  are  formed  by  the  direct  sub- 
stitution of  acetic  acid,  or  better,  of  acetyl  chloride,  chlori- 
nated acetyl  chlorides  ensuing  in  the  latter  case  as  inter- 
mediate products. 

Monochlor-acetic  acid  (Chloro-ethane  acid),  CH2C1«C02H, 
is  prepared  by  chlorinating  acetic  acid,  preferably  in  the  pre- 
sence of  acetic  anhydride,  sulphur,  or  phosphorus.  It  forms 
rhombic  prisms  or  tables  and  corrodes  the  epidermis.  Di- 
chlor-  acetic  acid,  CHC12  •  C02H,  is  more  conveniently  ob- 
tained by  warming  chloral  hydrate  with  potassium  cyanide 
(B.  10,  2120),  and  trichlor-  acetic  acid,  CC13  •  C02H,  by 


ACID  DERIVATIVES  171 

oxidizing  chloral  hydrate  with  nitric  acid.  The  former  de- 
composes with  boiling  alkali  to  oxalic  and  acetic  acids,  and 
the  latter  to  chloroform  and  carbon  dioxide.  Inverse  sub- 
stitution reconverts  tri-,  di-,  and  monochlor-acetic  acids  into 
acetic  acid  (Melsens,  1842). 

Sulpho-acetic  acid,  S03H»CH2«C02H,  forms  deliquescent 
prisms  containing  1J  mols.  H20  of  crystallization.  Its  salts 
crystallize  well.  Cyano-acetic  acid,  CN.CH2.C02H,  is  a 
crystalline  substance  melting  at  65°-66°  and  readily  soluble 
in  water;  it  decomposes  into  aceto-nitrile,  CH3»CN,  and  C02 
when  heated,  and  yields  malonic  acid  on  hydrolysis. 

a-Chloropropionic  acid,  CH3  •  CHOI  •  C02H,  is  obtained  by 
the  action  of  PC15  upon  lactic  acid,  and  decomposition  of  the 
lactyl  chloride,  CH3  •  CHC1  •  COC1,  by  water.  /Modopro- 
pionic  acid,  CH2I  •  CH2  •  C02H,  is  prepared  by  acting  upon 
gly eerie  acid,  CH2(OH) .  CH(OH)  •  C02H,  with  iodide  of  phos- 
phorus (exchange  of  2  OH  for  21  and  of  I  for  H);  also  by 
acting  on  acrylic  acid  with  hydriodic  acid.  It  forms  colour- 
less six-sided  tables  of  a  peculiar  odour;  m.-pt.  82°.  The  two 
cyanopropionic  acids,  C2H4(CN)  •  C02H,  give  the  two  succinic 
acids  when  hydrolysed. 

Chloro-  and  Bromo-crotonic  acids,  /3-Chloro-crotonic  acid 
(2-Chlwo-2-JButene  acid)  (m.-pt.  94°)  and  the  stereo -isomeric 
/3-Isochloro-crotonic  acid  (m.-pt.  59-5°)  are  formed  by  the 
action  of  PC15  on  ethyl  acetoacetate,  and  treatment  of  the 
product  with  water.  The  /3-chlor-iso-acid  volatilizes  with 
steam,  but  the  /?-chloro-acid  does  not. 


VII.  ACID  DERIVATIVES 


A  general  idea  of  the  kind  of  derivatives  to  which  acids 
give  rise  is  obtained  by  comparing  these  derivatives  with  cor- 
responding derivatives  of  the  saturated  monohydric  alcohols, 
e.g.  those  of  acetic  acid  with  those  derived  from  ethyl  alcohol: 


CH3-CH2.OH     Alcohol. 
CH3  •  CH2  •  ONa    Sodium  ethy  late. 

CH3  •  CH2  •  Cl        Ethyl  chloride. 
CHS.CH2.SH      Mercaptan. 
CH3.CH2'NH2    Ethylamine. 

CH3  •  CO  •  OH      Acetic  acid. 
CHS  •  CO  •  ONa    Sodium  acetate. 

CH3*CHiX>0      Ethy1  acetate- 
(CH8-CO)20        Acetic  anhydride. 
CH8  •  CO  •  Cl         Acetyl  chloride. 
CH8-  CO  •  SH       Thiacetic  acid. 
CHa-CO-NHz     Acetamide. 

172 


VII.   ACID  DERIVATIVES 


It  is  seen  that  as  regards  formulae  there  is  a  close  resem 
blance,  the  acetyl  group  taking  the  place  of  the  ethyl  group. 
Stated  generally,  the  acid  derivatives  contain  acyl  radicals  in 
place  of  the  alkyl  groups  contained  in  the  corresponding 
derivatives  of  alcohols. 

These  derivatives  are  obtained  by  methods  many  of  which 
are  perfectly  analogous  to  the  modes  of  formation  of  the  cor- 
responding alkyl  derivatives,  but  they  differ  characteristically 
from  these  by  being  less  stable  towards  hydrolysing  agents. 

A  number  of  other  derivatives,  viz.  amido-  and  imido- 
chlorides,  thiamides,  imido-thio-compounds,  and  amidines,  are 
peculiar  to  the  acids: 


CH8  •  CC12  -  NHR*Amido-chlorides. 
CH8  •  CC1 :  NR  Imido-chlorides. 
CH,.CS-NH3  Thiamides. 


CH8.C(NH)OH     Iimno-compounds. 
CH8.C(NH)SR      Imino-thio-   „ 
CH8.C(NH)(NH2)  Amidines. 


These  compounds  are  also  characterized  by  being  readily 
hydrolysed. 

A.  Esters  of  the  Fatty  Acids 

We  have  already  seen  that  mineral  acids  readily  give  rise  to 
esters  by  the  replacement  of  their  acidic  hydrogen  radicals  by 
alkyl  groups,  e.g.  S02(OH)2  —  S02(OEt)2.  In  exactly  the 
same  manner  the  typical  hydrogen  of  the  fatty  acids  can  be 
replaced  by  alkyl  groups,  and  we  get  esters  derived  from  the 
fatty  acids,  e.g.  ethyl  acetate,  CH3«C02Et.  Since  these  esters 
correspond  with  the  metallic  salts,  they  are  sometimes  termed 
alkyl  salts.  (Of.  CHg  .  C02K  and  CH8  •  C02Et.  ) 

Methods  of  Formation.  —  1.  By  direct  esterification,  i.e.  by 
direct  action  of  the  acid  on  the  alcohol: 


=  CH3.(X).ONa     -fH-OH 
H  =  CH3.(X).OC2H5H-  H-OH 

Although  the  equation  representing  the  reaction  is  analogous 
to  that  representing  the  neutralization  of  acetic  acid  by  an 
alkali,  the  process  of  esterification  differs  from  that  of  neutrali- 
zation in  two  respects. 

(1)  The  reaction  proceeds  but  slowly;  thus,  in  the  esteri- 
fication of  acetic  acid  by  ethyl  alcohol  the  limit  of  the  reaction 
at  the  boiling-point  is  not  reached  until  after  the  lapse  of 


*  R  signifies  an  alkyl  radical  either  alphyl  or  aryl. 


ESTERIFICATION  173 

several  hours,  and  even  then  only  two-thirds  of  the  acid  have 
been  transformed  into  ester. 

(2)  The  reaction  is  a  reversible  or  balanced  one,  and  hence 
is  never  complete.  The  water  which  is  formed  during  the 
process  of  esterification  tends  to  hydrolyse  the  ester  back  into 
acid  and  alcohol  : 


Thus,  when  equivalent  quantities  of  acetic  acid  and  ethyl 
alcohol  are  employed,  only  some  66  per  cent  of  the  acid 
becomes  transformed  into  ester.  It  can  readily  be  shown,  by 
aid  of  Guldberg-PFaage's  law  of  mass  action,  that  by  employing 
an  excess  of  alcohol  a  larger  proportion  of  acid  will  be  con- 
verted into  ester.  Thus,  in  the  above  equation,  if  the  original 
concentrations  of  the  four  substances  expressed  in  gram  mole- 
cules be  denoted  by  a,  b,  o  and  o,  and  the  velocity  constants 
of  the  direct  and  reverse  reactions  by  k^  and  k2  respectively, 
then  after  time  t  equilibrium  will  be  established;  and  if  we 
assume  x  gram  molecules  of  acid  have  been  esterified,  then  the 
concentrations  of  the  four  substances  will  be  a  —  x,  b  —  x, 
x  and  x.  The  rate  of  the  direct  reaction  can  be  denoted  by 
&!  (a  —  x  )  (b  —  x),  and  that  of  the  reverse  by  &2  x2  (Guldberg 
and  Waage).  When  equilibrium  is  established,  the  two 
reactions  will  proceed  at  the  same  rate,  and 

k,(a-x}(b-x)  =  £2*2, 

or  (a—x)  (b—x)  _  constant  for  a  given  temperature. 
x- 

In  the  case  of  acetic  acid  and  ethyl  alcohol,  using  gram 
molecular  proportions,  i.e.  a  =  b  =  1,  we  find  that  equilibrium 
is  established  when  some  two-thirds  of  acid  are  esterified. 
Thus 

(!—  i)(l-"f)  =  constant, 
and  the  constant  becomes  equal  to  J. 

Then,  supposing  we  alter  the  proportions  of  acid  and  alcohol, 
using  2  gram  molecules  of  alcohol  to  1  of  acid,  we  have  — 


4 
=  -85  (appro*.), 


174  VIL    ACID  DERIVATIVES 

0 

and  thus  85  per  cent  of  the  acid  will  have  been  esterified  in 
place  of  the  66  per  cent  when  only  1  gram.  mol.  of  alcohol 
was  used.  The  reversible  nature  of  the  reaction  is  of  especial 
importance  in  the  preparation  of  ethyl  acetate,  and  in  this 
case  the  difficulty  is  overcome  by  the  addition  of  a  moderate 
amount  of  concentrated  sulphuric  acid,  which  is  ordinarily 
supposed  to  react  with  the  water,  and  thus  prevent  its  hydro- 
lysing  the  ester.  (Compare  also  Wade,  J.  C.  S.  1905,  1656.) 

It  is  worthy  of  note  that  the  limit  of  esterification  does  not 
vary  to  any  large  extent  with  the  temperature.  Thus,  in  the 
case  mentioned  above,  the  limit  at  10°  is  65 '2  per  cent,  and  at 
220°  it  is  only  66*5  per  cent. 

With  most  of  the  higher  esters,  and  more  especially  the 
esters  in  the  aromatic  series,  the  limit  of  esterification  is  much 
higher,  as  the  esters  are  not  so  readily  hydrolysable.  In  these 
cases,  however,  the  rates  at  which  the  esters  are  formed  are 
extremely  slow,  and  a  catalytic  agent  is  therefore  introduced. 
The  two  common  catalytic  agents  employed  are:  (1)  A  small 
amount  of  dry  hydrogen  chloride.  At  one  time  it  was  cus- 
tomary to  saturate  the  boiling  alcoholic  solution  of  the  acid 
with  hydrogen  chloride,  but  the  researches  of  E.  Fischer  and 
Sprier  (B.  1895,  28,  3201,  3252)  have  shown  that  the  addition 
of  3  per  cent  of  dry  hydrogen  chloride  to  the  alcoholic  solu- 
tion is  quite  sufficient.  (2)  A  small  amount  of  concentrated 
sulphuric  acid,  which  acts  in  much  the  same  manner  as  the 
hydrogen  chloride.  The  use  of  these  reagents  is  not  to  raise 
the  limit  of  esterification,  but  to  accelerate  the  production. 
In  most  cases,  using  the  catalytic  method  at  the  boiling-point 
of  the  alcohol,  the  reaction  is  complete  after  three  hours,  and 
a  90-95  per  cent  yield  of  ester  can  be  obtained  by  pouring 
into  water. 

A  number  of  researches  have  been  made  as  to  the  influence 
of  the  constitution  of  the  acid  and  of  the  alcohol  on  the  rate 
of  esterification,  i.e.  the  amount  of  ester  formed  in  unit  time. 
Menschutkin,  who  employed  the  direct  esterification  method 
without  a  catalytic  agent,  i.e.  the  so-called  auto -catalytic 
method,  found  that  primary  acids,  i.e.  R»CH2-C02H,  were 
esterified  most  quickly;  secondary  acids,  EE'CH-C02H,  were 
intermediate;  and  tertiary  acids,  RR'R"C'C02H,  least  readily 
when  the  same  alcohol  was  employed.  Other  researches  tend 
to  show  that  strong  acids  react  with  alcohol  more  readily  than 
feeble  acids  in  the  absence  of  a  catalyst. 

The  velocity  of  esterification  has  also  been  determined  for 


ESTERIFICATION  175 

a  number  of  acids  employing  the  catalytic  metnod  (HC1). 
From  the  equation  we  should  expect  the  reaction  to  be  a 
bimolecular  reaction,  or  a  reaction  of  the  second  order;  by 
altering  the  conditions,  namely,  by  taking  a  large  excess  of 
alcohol  as  compared  with  the  acid,  the  concentration  of  the 
alcohol  may  be  regarded  as  constant,  and  the  reaction  then 
becomes  unimolecular  (H.  Goldschmidt)  and  may  be  studied 
by  the  aid  of  the  equation  for  unimolecular  reactions, 

K  =  -  log.  —  -  —  ;  where  K  =  the  velocity  constant,  t  — 

time,  a  =  concentration  of  the  acid  at  the  beginning  of  the  ex- 
periment expressed  in  c.c.  of  standard  alkali,  and  a  —  x  —  con- 
centration of  the  acid  after  the  lapse  of  time  t. 

Using  this  method,  it  is  found  that  the  introduction  of  any 
substituent  (CH3,  Cl,  Br,  I,  C6H5,  &c.)  into  the  acetic  acid 
molecule  always  lowers  the  velocity  of  esterification,  the 
introduction  of  two  such  radicals,  e.g.  CHBr2«C02H,  lowers 
the  constant  to  a  still  greater  extent,  and  when  all  three 
hydrogens  are  replaced  by  substituents,  e.g.  C(CH3)3«C02H, 
the  acid  is  esterified  very  slowly  indeed  as  compared  with 
acetic  acid. 

These  examples  afford  an  extremely  good  instance  of  what 
is  now  generally  termed  steric  retardation,  or  the  retardation 
of  a  chemical  reaction  by  the  spatial  relationships  of  radicals 
introduced  into  a  molecule. 

The  common  theory  of  the  process  of  esterification  is  that 
there  is  first  direct  union  between  a  molecule  of  the  acid  and 
of  the  alcohol  : 


+  R'OH  = 

X)H, 

yielding  a  dihydroxylic  compound,  which  immediately  elimi- 
nates water,  yielding  the  ester  R-C<^J  .  The  introduction 

of  radicals  into  the  CH3  group  of  the  acetic  acid  molecule  by 
filling  up  the  space  renders  the  formation  of  such  additive 
compounds  much  more  difficult,  and  hence  the  retardation  of 
esterification  (Wegscheider). 

The  influence  of  the  hydrogen  chloride  is  purely  catalytic; 
it  remains  unchanged  at  the  end  of  the  reaction.  Its  catalys- 
ing effect  is  undoubtedly  due  to  to  the  hydrions  it  generates, 
as  strong  acids  (HC1,  HBr)  are  much  better  catalysing  agents 


176  VII.    ACID  DERIVATIVES 

than  weaker  acids  (picric  acid).  (Cf.  Goldschmidt,  B.  1895,  28, 
3218;  Sudborough  and  others,  J.  C.  S.  1898,  81;  1899,  467; 
1904,  534;  1905,  1840.) 

2.  By  the  action  of  an  acid  chloride  upon  an  alcohol  or  its 
sodium  compound  (cf.  p.  179): 


3.  By  the  action  of  an  alkyl  haloid  upon  the  salt  of  the 
acid: 

C2H5C1  +  CH3CO.ONa  =  CH3.CO.OC2H6  -f  NaCl. 

As  a  rule,  an  alkyl  iodide  and  the  silver  salt  of  the  acid  are 
employed.  The  ester  can  then  be  separated  from  the  solid 
silver  iodide  and  distilled.  Occasionally  the  potassium  salt 
and  methyl  sulphate  are  used.  Reactions  2  and  3  are  of  very 
general  application,  and  are  largely  made  use  of  when  an  ester 
cannot  readily  be  obtained  by  the  catalytic  method  of  esteri- 
fication. 

Properties.  —  The  esters  are  mostly  neutral  liquids  which 
volatilize  without  decomposition;  only  those  which  contain  a 
small  number  of  carbon  atoms  in  the  molecule  are  soluble  in 
water,  e.g.  ethyl  acetate  (1:14). 

1.  "Hydrolysis.  —  They  are  all  hydrolysed  (saponified),  i.e. 
resolved  back  into  alcohol  and  acid,  when  heated,  or  better, 
superheated,  with  water,  or  when  boiled  with  aqueous  solutions 
of  strong  alkalis  or  mineral  acids;  with  the  simpler  esters  this 
hydrolysis  is  complete  when  the  ester  is  allowed  to  remain  for 
some  time  in  contact  with  water  or  dilute  alkali. 

The  hydrolysis  of  an  ester  under  the  infli^nce  of  water  or 
of  mineral  acids  may  be  represented  by  the  equation: 

K.CO2B'4-H.OH  =  K-CO-jH  +  K'-OH, 

and  may  be  studied  by  the  aid  of  the  general  equation  for 

a  uni-molecular  reaction,  K  =  -  log.  —  —  ,  since  the  concen- 

t          a  —  x 

tration  of  the  water,  if  a  large  excess  is  used,  may  be  regarded 
as  constant. 

The  action  of  the  mineral  acid  is  purely  catalytic.  The 
same  result  might  ultimately  be  obtained  by  using  water  alone, 
but  is  considerably  accelerated  by  using  a  small  amount  of 
a  strong  mineral  acid  (HC1,  H2S04).  Weak  acids  also  ac- 
celerate the  hydrolysis  of  the  ester,  but  to  a  less  extent.  Ifc 


HYDROLYSIS  OF  ESTEKS  177 

has  been  found,  using  the  same  ester  and  equivalent  quantities 
of  different  acids,  that  the  rate  of  hydrolysis  is  directly  pro- 
portional to  the  strength  of  the  acid.  In  other  words,  the 
catalysing  influence  of  different  acids  is  due  to  the  hydrions. 
The  hydrolysis  of  an  ester  by  alkalis  is  represented  by  the 
equation:  E .  CO .  OB'  +  NaOH  =  E-CO-ONa  +  R'-OH, 
and  as  it  is  analogous  to  the  preparation  of  soaps  by  the  action 
of  alkalis  on  fats  (p.  158),  is  commonly  termed  Saponification. 
This  is  a  bimolecular  reaction,  and  if  equivalent  quantities  of 
ester  and  alkali  are  employed  in  solution,  can  be  studied  by 

aid  of  the  equation  K  =  - •—7-^- — r,  where  t  =  time,  a  =  initial 
t  a(a  —  x) 

concentration  of  alkali  and  of  ester,  a  —  x  =  concentration  of 
these  after  time  t.  The  concentrations  can  readily  be  deter- 
mined by  direct  titration  with  standard  acid,  and  the  number  of 
cubic  centimetres  of  acid  introduced  directly  into  the  equation. 

It  has  been  found  that  when  different  alkalis  are  employed, 
their  hydrolysing  effect  is  proportional  to  their  strengths,  i.e. 
is  due  to  the  free  hydroxyl  ions.  Different  esters  are  hydro- 
lysed  at  very  different  rates  by  the  same  alkali;  the  rate 
appears  to  depend  on  the  complexity  of  the  molecule,  i.e. 
the  number  of  substituents  present,  and  also  on  the  nature 
of  these  substituents,  viz.  whether  they  are  of  a  positive  or 
negative  nature.  It  has  been  found  that  CC13»C02C2H5  is 
hydrolysed  by  alcoholic  potash  much  more  readily  than  ethyl 
acetate  itself,  owing  to  the  negative  nature  of  the  chlorine  sub- 
stituents. (Compare  A.  228,  257;  232,  103;  J.  C.  S,  1899,  482.) 

In  all  cases  it  has  been  found  that,  comparing  solutions  of 
equal  strength,  e.g.  N/10,  a  strong  alkali  is  a  much  better 
hydrolysing  agent  than  a  strong  acid. 

2.  A  characteristic  reaction  of  methyl  and  ethyl  esters  is 
that  they  exchange  OMe^methoxy)  or  OEt  (ethoxy)  groups 
for  NH2  on  treatment  with  strong  ammonia,  thus  yielding 
acid  amides,  e.g.  CH3»CO-NH2. 

3.  Phosphorus  pentachloride  decomposes  most  esters,  yield- 
ing an  alkyl  chloride  and  an  acyl  chloride,  the  0  of  the  »OEt 
group  being  replaced  by  two  chlorine  atoms 

4.  Ethyl  esters  are  readily  transformed  into  methyl  esters, 
R.COoEt  — >-  R.C02Me,  by  warming  with  methyl  alcohol  and 
a  catalyst  (CH3ONa,  HC1).     The  reaction  is  reversible,  and  is 
termed  alcoholysis. 

5.  Sodium  methoxide  combines  with  the  esters  to  form  un- 

(B480)  M 


178  VIL    ACID  DERIVATIVES 


x 

stable  additive  compounds,  R«C^-OCH,,  which  are  derivatives 

' 


of  "ortho-acids".     (See  p.  142;  also  B.  20,  646.) 

The  odour  and  taste  of  many  of  the  esters  is  so  agreeable 
that  they  are  manufactured  upon  a  large  scale,  and  employed 
as  fruit  essences. 

Ethyl  formate,  H-CO.OC2H5,  b.-pt.  55°,  is  employed  in 
the  manufacture  of  artificial  rum  or  arrak.  Ethyl  acetate, 
acetic  ether,  CH3.CO-OC2Hr,  b.-pt.  75°,  is  used  internally  as 
a  medicine.  Amyl  acetate,  CH3-  CO.  OC5Hn,  b.-pt.  148°.  The 
alcoholic  solution  of  this  forms  the  essence  of  pears.  Ethyl 
butyrate,  CH3(CH.7)2CO'OC2H5,  is  the  essence  of  pine-apples. 
Iso-amyl  iso-valerate,  C4H9  .  CO  •  0  •  OC5Hn,  b.-pt.  196°,  finds 
application  as  apple  oil  or  apple  ether.  Cetyl  palmitate, 
C15H31.CO.OC16H33,  ceryl  cerotate,  C2,H51  •  CO  •  OC26H53,  and 
melissic  palmitate,  C15H81«CO«0«C3Ji6j,  are  constituents  of 
waxes.  (See  Wax  Varieties,  p.  158V) 

When  the  esters  of  the  acids  of  high  molecular  weight  are 
distilled  under  the  ordinary  pressure  and  not  in  a  vacuum,  they 
decompose  into  an  olefine  and  a  fatty  acid.  (See  p.  46.) 

homers.  —  All  esters  containing  the  same  number  of  C  atoms 
in  the  molecule,  and  derived  from  the  monohydric  saturated 
alcohols  and  the  fatty  acids,  are  isomeric.  Thus  methyl  buty- 
rate is  isomeric  not  only  with  ethyl  propionate  but  also  with 
propyl  acetate'  and  with  butyl  formate.  Further,  all  esters 
are  isomeric  with  the  monobasic  acids  which  contain  an  equal 
number  of  carbon  atoms,  e.g.  the  esters  just  mentioned  are 
isomeric  with  the  valeric  acids.  (See  Metamerism,  p.  87.) 

Further  cases  of  isomerism  occur  when  the  alcohol  on  the 
one  hand,  or  the  acid  on  the  other,  is  unsaturated,  e.g.  allyl 
propionate  and  propyl  acrylate. 

B.  Acid  Chlorides,  Bromides,  &e. 

Acid  chlorides  are  the  compounds  derived  from  the  acids  by 
the  replacement  of  the  hydroxyl  group  by  chlorine  : 

B-CO-OH  —  K-CO-C1. 

1.  They  are  usually  prepared  by  the  action  of  the  chlo- 
rides of  phosphorus,  PC13  and  PC15,  upon  the  acids  or  their 
salts  : 


C3HrCO.OH4-PCl5  =  0^.00-01  +  POC1,  +  HCL 


ACID   CHLORIDES  179 

The  acid  chloric^  is  separated  from  the  POC13  formed  at  the 
same  time  by  fractional  distillation.  In  the  case  of  acetic  acid 
PC13  is  conveniently  used : 

3CH3.CO.OH  +  PC13  =  SCHg-CO-Cl  +  POaHg. 

Phosphorus  oxychloride,  POC13,  may  also  be  allowed  to  act 
upon  the  alkali  salts  of  the  acids;  when  the  latter  are  present 
in  excess,  acid  anhydrides  are  produced  (p.  180).  Thionyl- 
chloride,  SOC12,  and  the  acid  are  frequently  used,  as  the  only 
other  product  is  S02. 

2.  By  the  action  of  chlorine  upon  the  aldehydes  in  the 
absence  of  water:  CH3.CHO  +  C12  =  CH8.COC1  +  HC1. 


Properties. — The  acid  chlorides  are  suffocating  liquids  which 
fume  in  the  air,  distil  without  decomposition,  and  are  recon- 
verted by  water,  in  many  cases  at  the  ordinary  temperature, 
into  the  corresponding  acids  and  hydrochloric  acid : 

CHg.CO-Cl-f  H2O  =  CH3.CO.OH-f  HC1. 

They  are  thus  more  readily  decomposed  than  the  alkyl 
chlorides.  When  ,the  chlorides  are  warmed  with  alcohols,  the 
chlorine  is  replaced  by  alkyloxy  groups,  e.g.  OCH3,  OC2H5, 
and  in  this  way  esters  are  formed.  With  ammonia  they  yield 
acid  amides,  E.CO-NH2.  With  the  sodium  salts  of  the  fatty 
acids  they  yield  acid  anhydrides.  With  organo-magnesium  com- 
pound they  first  form  ketones,  and  then  tertiary  alcohols  (see 
p.  72).  With  silver  cyanide  acyl  cyanides  (e.g.  CH3«CO«CN, 
acetyl  cyanide)  are  formed,  and  thfs^on  hydrolysis  with 
concentrated  hydrochloric  acid  yield  ketonic  acids,  CH3-CO- 
COOH. 

Formyl  chloride  is  not  known. 

Acetyl  chloride  (Ethanoyl  chloride),  CH3-COC1,  is  a  mobile, 
colourless  liquid  of  suffocating  odour.  Boils  at  55°,  has  a 
sp.  gr.  1-13  at  0°,  reacts  extremely  vigorously  with  water  and 
ammonium  hydroxide,  and  is  a  reagent  of  exceptional  im- 
portance, since  it  serves  for  the  conversion  of  the  alcohols  and 
primary  and  secondary  amines  into  their  acetyl  derivatives. 
It  is  thus  frequently  used  for  detecting  OH,  NH2  or  NH 
groups  in  organic  compounds.  The  compound  under  exami- 
nation is  heated  with  acetyl  chloride  (or  even  better,  acetic 
anhydride),  and  the  pure  product  either  analysed  or  hydro- 
lysed,  and  acetic  acid  tested  for  in  the  products  of  hydrolysis 
(see  p.  201). 


180  VII.    ACID   DERIVATIVES 

The  boiling-points  of  the  acid  chlorides  are  always  con- 
siderably lower  than  those  of  the  corresponding  acids. 

Acid  bromides  and  iodides  are  known  and  closely  resemble 
the  chlorides.  Their  boiling-points  are  higher. 

C.  Acid  Anhydrides  •  ' 

Corresponding  with  the  monobasic  fatty  acids  there  are  ;^^^ 
hydrides,  which  may  be  regarded  as  derived  from  two  molecul^M 
of  the  acid  by  the  elimination  of  a  molecule  of  water,  e.g.; 

CH3.CO.OH  _  CH3.CO\ 
~ 


They  may  also  be  considered  as  acyl  oxides.  For  instance, 
(CH3.CO)20  =  acetyl  oxide. 

Preparation.  —  1.  They  cannot  as  a  rule  be  obtained  by  the 
direct  withdrawal  of  water  from  the  acids,  but  by  the  action 
of  acid  chlorides  upon  the  alkali  salts  of  the  acids: 

CH3.CO.;Ci  +  Na;O.CO.CH3  =  (CH3-CO)2O  +  NaCl. 

A  very  convenient  method  for  preparing  them  is  by  the 
action  of  phosphorus  oxychloride  on  the  sodium  salts  of  the 
acids,  care  being  taken  that  sufficient  of  the  dry  sodium  salt 
is  used  to  decompose  the  acid  chloride  first  formed  (see  p.  179)  : 

=  2CH3-COC1  +  NaCl  +  NaPO3. 


2.  By  the  action  of  phosgene  on  the  acids  (B.  17,  1286): 
2CH3.CO.OH  +  COC12  =  (CH3.CO)20  +  C02 


3.  The  anhydrides  of  the  higher  acids  are  conveniently 
prepared  by  the  action  of  acetic  anhydride  on  their  sodium 
salts. 

Properties.  —  The  majority  of  the  acid  anhydrides  are  liquids, 
but  those  of  higher  molecular  weight  solids,  of  neutral  reaction, 
and  soluble  in  alcohol  and  ether.  They  are  non-miscible  with 
water,  but  are  gradually  hydrolysed  by  it  to  the  free  acids. 
Dilute  alkalis  decompose  them  readily.  When  warmed  with 
alcohols  they  yield  esters;  with  ammonia,  acid  amides;  and 
with  hydrogen  chloride,  free  acid  and  acid  chloride: 

(CH3  •  CO)2O  +  HC1  =  CH3  •  CO  •  Cl  +  CH3  •  CO  •  OH. 
The  boilin  fir-point  of  an  acid  anhydride  is  higher  than  that 


THIO-ACIDS  181 

of  the  corresponding  acid,  although  an  ether  boils  at  a  lower 

temperature  than  the  corresponding  alcohol,  e.g.  EtOH  78°; 

Et20  35°;  AcOH  118°;  Ac20  137°. 

Acetic  anhydride,  (CH3.CO)20,  is  a  mobile  liquid  of  suffocat- 

ing odour,  boiling  at  137°,  and  having  a  sp.  gr.  of  1*073  at  20°. 

Like  acetyl  chloride  it  is  a  reagent  of  great  importance,  and 
largely  made  use  of  in  testing  for  and  estimating  hydroxyl 
ups  in  carbon  compounds,  and  for  converting  primary  and 
ndary  amines  into  acetyl  derivatives. 

anhydrides  containing  two  different  acyl  groups  are 


TT 

also  known  (Gerhardt,  Williamson),  e.g.  p,2^3  n^>0.    When  dis- 


tilled  they  yield  the  two  simple  anhydrides. 

Acyl  peroxides  have  also  been  prepared.  Acetyl  peroxide, 
(C2H30)202,  is  a  thick  liquid  insoluble  in  water,  which  acts  as 
a  strong  oxidizing  agent  and  explodes  when  heated;  it  is 
prepared  by  the  action  of  barium  peroxide,  Ba02,  upon  acetic 
anhydride. 

Numerous  other  peroxides  have  been  prepared  recently  by 
Baey&r  and  Tilliger  (B.  1901,  34,  738)  by  means  of  hydrogen 
peroxide  in  the  presence  of  potassium  hydroxide.  Among  the 
simpler  of  these  peroxides  may  be  mentioned  ethyl  hydrogen 
peroxide,  C2H5.0.0-H,  a  colourless  liquid;  diethyl  peroxide, 
C2H5.0-O.C2H5,  a  liquid  boiling  at  65°;  acetone  peroxide, 
(C3H602)2,  boiling  at  132°;  and  triacetone  peroxide,  (C3H602)3, 
melting  at  97°.  Many  of  these  compounds  are  explosive. 

D.  Thio-aeids  and  Thio-anhydrides 

Just  as  sulphur  can  replace  oxygen  in  the  alcohols  and 
ethers,  giving  rise  to  mercaptans  and  alkyl  sulphides,  so  it 
can  replace  oxygen  in  the  carboxylic  acids,  giving  rise  to  (1) 
R-CO-SH,  thiolic  acids;  (2)  R.CS-OH,  thionic  acids;  and  (3) 
R-CS-SH,  thion-thiolic  acids. 

Thiacetic  acid  (Ethane-tUolic  add),  CH3.CO.SH,  is  a  colour- 
less liquid  boiling  below  100°;  it  smells  of  acetic  acid  and 
sulphuretted  hydrogen,  and  is  readily  decomposed  by  water 
into  these  two  components.  It  is  prepared  from  acetic  acid 
and  phosphorus  pentasulphide,  P2S6.  The  other  thio-compounds 
are  likewise  readily  hydrolysed,  yielding  acetic  acid  and  hy- 
drogen sulphide. 


182  VII.    ACID  DERIVATIVES 

E.  Acid  Amides  and  Hydrazides 

Amides. — An  acid  amide  is  the  compound  derived  from  the 
acid  by  the  introduction  of  the  amido*  group  in  place  of  the 
hydroxyl  radical  of  the  carboxylic  group: 

E-CO-OH  —  E-CO.NH2. 

They  may  also  be  regarded  as  derived  from  ammonia  by-| 
the  replacement  of  a  hydrogen  atom  by  an  acyl  group,  e.g.  ^ 
NH2  •  CO  •  CH3.     Secondary  and  tertiary  amides,'  e.g.  NH(CO  • 
CH3)2,  and  N(CO«CH3)3,  are  known,  but  are  of  relatively 
small  importance. 

Modes  of  Formation.  —  1.  By  the  dry  distillation  of  the 
ammonium  salts  of  the  fatty  acids: 

CH3.CO-ONH4  =  CH3.(X).NH2  +  H2O. 

2.  By  addition  of  water  to  the  alkyl  cyanides  (nitriles) : 

=  CH3.CO.NH2. 


This  addition  of  water  is  frequently  effected  by  dissolving 
the  nitrile  in  concentrated  sulphuric  acid,  or  in  acetic  and 
concentrated  sulphuric  acids,  or  by  shaking  with  concentrated 
hydrochloric  acid  in  the  cold;  also,  and  often  quantitatively, 
by  hydrogen  peroxide,  H202,  in  alkaline  solution.  In  some 
cases  a  further  addition  of  water  occurs,  and  the  ammonium 
salt  of  the  acid  is  formed. 

3.  By  the  action  of  acid  chlorides  or  acid  anhydrides  upon 
aqueous  ammonia  or  solid  ammonium  carbonate;   if  amines 
are  employed  here,  in  place  of  ammonia,  alkylated  amides 
are  formed: 

CH3.COCl-f2NH3  =  OE3.CONH2-J-NH4C1. 

4.  By  heating  esters  with  ammonia  solution,  sometimes  even 
on  shaking  in  the  cold: 

CH3.CO-OC2H6  +  NH3  =  CH3.00-NH2-f  C2H6OH. 

Properties. — 1.  With  the  exception  of  formamide  they  are 
colourless  crystalline  compounds,  volatile  without  decomposi- 
tion, but  with  relatively  high  boiling-points.  The  following 

*  The  NH4  group  it  usually  termed  an  amino  group  when  present  in  a 
primary  amine,  l>ut  an  amido  group  when  present  in  an  acid  amide. 


ACID  AMIDES  183 

comparison  of  boiling-points  is  interesting,  as  the  order  is  the 
same  for  most  groups:  — 

Acetyl  Ethyl  Acetic  Acetic 

chloride.        acetate.  acid.  anhydride.    Acetamide. 

Boiling-point        55°  78°  117°  137°  222° 

2.  The  lower  members  are  soluble  in  water,  and  although 
derivatives  of  ammonia  are,  unlike  most  amines,  practically 
neutral,  the  strongly  positive  character  of  the  hydrogen  atoms 
of  the  ammonia  being  cancelled  by  the  entrance  of  the  nega- 
tive acyl  radical.     Still,  the  primary  amides  are  capable  of 
forming  additive  compounds  with  some  acids,  e.g.  acetamide 
yields  the  compound  (C2H30  •  NH2)2HC1,  "acetamide  hydro- 
chloride";  these  are,  however,  unstable,  and  are  decomposed 
for  the  most  part  by  water  alone.     On  the  other  hand,  the 
hydrogen  of  the  amido  group  can  be  replaced  by  particular 
metals,  especially  mercury  (also  sodium;  cf.  B.  23,  3037;  28, 
2353),  the  amides,  therefore,  playing  the  part  of  weak  acids 
in  the  compounds  so  obtained,  e.g.  mercury  acetamide,  (CH3  • 
CONH)2Hg. 

3.  The  amides  are  readily  hydrolysed,  more  especially  by 
alkalis,  to  the  free  acid  and  ammonia.     Alkylated  amides  on 
hydrolysis  yield  the  acid  (or  sodium  salt)  and  an  amine  (not 
ammonia).     Amines  are  not  decomposed  by  alkalis. 

CH3.CO.NHC2H5  +  NaOH  =  CHg-CO-ONa  +  C2H6NH2. 


Hydrolysis  of  Acid  Amides.  —  The  velocity  of  hydrolysis  of 
the  amides  of  the  common  fatty  acids  has  been  determined  by 
Crocker  and  Lowe  (J.  C.  S.  1907,  91,  593  and  952),  using  an 
electro-conductivity  method.  With  sodium  hydroxide  and  also 
hydrochloric  acid,  formamide  is  hydrolysed  most  readily,  and 
valeramide  least  readily. 

4.  Nitrous  acid  converts  the  primary  amides  into  the  corre- 
sponding acids,  with  liberation  of  nitrogen  : 

CH3.CO.NH2  +  N02H  =  CHg-CO-OH  +  N,  +  H2O. 

This  reaction  is  a  general  one,  and  corresponds  exactly  with 
the  action  of  nitrous  acid  upon  the  primary  amines  (p.  108). 

5.  Nitriles  (see  p.  101)  are  formed  by  heating  with  P4010, 
P2S5,  and  PC15  (see  pp.  185  and  186). 

6.  If  bromine  in  the  presence  of  alkali  is  allowed  to  act 
upon   primary  amides,  bromamides,  B»CO«NHBr,  e.g.  CH3- 
CO.NHBr,   aceto-bromamide  (colourless  rectangular  plates), 
are  first  formed,  and  these  are  decomposed  by  the  alkali  into 


184  VII.   ACID  DERIVATIVES 

a  primary  amine,  carbon  dioxide  and  potassium  hydroxide. 
If  less  bromine  is  used,  urea  derivatives  are  formed,  e.g.  methyl- 
acetyl-urea,  CH3.NH.CO.NH.CO.CH3,  which  react  with  ex- 
cess of  alkali,  yielding  primary  amines  —  in  this  case  CH3  •  NH2 
—  containing  1  atom  of  carbon  less  than  the  original  amide. 
This  is  an  excellent  method  for  the  preparation  of  amines 
from  Cj  to  C6,  but  less  valuable  for  those  from  C6  onwards, 
as  in  the  case  of  the  higher  compounds  the  production  of  amine 
diminishes,  a  nitrile  being  formed  instead  by  the  further  action 
of  the  bromine  (see  below).  Such  nitriles  CnH2n+1«CN,  in 
which  n  >  4,  can  therefore  be  obtained  directly  from  the  amine 
by  the  action  of  bromine  and  alkali  upon  it,  thus  :  — 


C7H16.CH2.NH2  +  2Br2  =  CVH15.CH2.NBr2  +  2HBr 


(Reversal  of  the  Mendius  reaction,  p.  106;  cf.  Hofmann,  B.  15, 
407,  752;  17,  1407,  1920;  18,  2737.) 

Since  these  nitriles  on  hydrolysis  yield  acids  containing 
1  atom  of  carbon  less  than  the  amide  originally  taken,  this 
reaction  renders  it  possible  to  descend  in  the  series  successively 
from  one  acid  to  another  (compare  p.  160),  e.g.  : 

C0H13.CH2.C02H   —   C6H13.CH2.CO.NH2  —   C6HirCH2.NH2 
—  C6H13.CH2.NBr2  —  C6H13.CN  —  C6H13.CO2H. 

This  has  been  done  in  the  case  of  the  normal  acids  from  C14 
to  Cp  and  it  furnishes  a  further  proof  of  their  normal  con- 
stitution. 

Constitution.  —  Most  of  the  methods  of  formation  and  many 
of  the  properties  of  the  amides  point  to  the  constitutional  for- 
mula (I).  A  second  formula  is  possible  (II),  in  favour  of  which 
certain  arguments  have  been  adduced  (B.  22,  3273;  23,  103; 
25,  1435): 


(I)  R.C  (II) 


This  last  formula  easily  passes  into  the  first  by  the  migration 
of  a  hydrogen  atom,  and  most  of  the  reactions  of  the  simple 
amides  are  explicable  almost  equally  well  by  either  formula. 
(Cf.  Titherley,  J.  C.  S.  1897,  468;  1901,  407.) 

We  thus  have  a  single  compound  which  appears  to  possess, 
according  to  its  reactions,  two  distinct  formulae.  Such  a  sub- 
stance is  usually  termed  a  tautomeric  substance. 


AMIDO-  AND   IMIDO-CHLORIDES  185 

On  alkylation,  under  different  conditions,  it  is  possible  to 
obtain  two  distinct  types  of  mono-alkylated  amides,  viz.: 

and    (n) 

These  differ  as  regards  physical  and  chemical  properties; 
they  are  isomeric.  Compounds  of  type  I  closely  resemble  the 
original  amides;  compounds  of  type  II  are  usually  known  as 
imino  ethers,  and  differ  to  a  large  extent  (p.  187). 

In  many  other  cases  we  find  that  a  tautomeric  substance 
gives  rise  to  two  distinct  groups  of  alkyl  derivatives  (see 
Cyanogen  Derivatives). 

Formamide  (Methane-amide),  HCO-NH2,  is  a  liquid  readily 
soluble  in  water  and  alcohol.  It  boils  with  partial  decom- 
position at  about  200°.  When  quickly  heated  it  decomposes 
into  CO  and  NH3,  and  with  phosphorus  pentoxide  it  yields 
hydrocyanic  acid. 

Acetamide,  Ethane-amide,  CH3-CO'NH2,  forms  long  needles, 
readily  soluble  in  water  and  alcohol.  It  melts  at  82°,  boils  at 
222°,  and  when  pure  has  no  odour. 

Di-acetamide,  (C2H30)2NH.     M.-pt.  78°;  b.-pt.  223°. 

HYDRAZIDES 

Just  as  ammonia  by  the  introduction  of  acyl  groups  yields 
the  acid  amides,  so  hydrazine  yields  the  acid  hydrazides,  e.g. 
acetyl  hydrazine  or  acet-hydrazide,  CH3  •  CO  •  NH  •  NH2.  They 
are  formed  by  the  action  of  esters  on  hydrazine.  They  are 
basic  in  character,  are  readily  hydrolysed,  and  possess  reduc- 
ing properties.  With  nitrous  acid  they  yield  acid  azides,  e.g. 

||  ,  which  are  acyl  derivatives  of  hydrazoic  acid, 


, 
^  || 


(N3H). 

All  4  hydrogen  atoms  in  hydrazine  can  be  replaced  by  acyl 
radicals  in  much  the  same  manner  as  the  3  hydrogen  atoms  in 
the  ammonia  molecule  can.  The  products  are  termed  di-,  tri-, 
and  tetra-hydrazides,  e.g.  tetra-acet-hydrazide,  Ac2N-NAc2. 

F.  Amido-ehlorides  and  Imido-ehlorides 

By  the  action  of  PC15  upon  the  primary  amides  an  ex- 
change of  C12  for  O  takes  place,  giving  rise  in  the  first  in- 
stance to  the  so-called  amido-chlorides,  e.g.  acetdichloroamide, 


186  VII.    ACID  DERIVATIVES 

CH3'CC12»NH2;  these  are  extremely  unstable  compounds, 
being  converted  by  water  into  amide  and  hydrochloric  acid, 
and  readily  giving  up  HC1,  with  formation  of  imido-chlorides, 
e.g.  CH3»CC1:NH,  acetchloroimide.  The  imido-chloroides  are 
also  relatively  unstable,  yielding  with  water  the  amide  and 
hydrochloric  acid.  When  heated,  they  break  up  into  nitrile 
and  hydrochloric  acid. 

The  alkylated  amides  (p.  182)  also  yield  chloroamides,  e.g. 
CH3.CO.NH.C2H5  gives  CH3.CC12.NH.C2H5,  ethyl  acet- 
chloroamide,  and  CH3.CO-NK2  gives  CH3.CC12.NK2;  if 
these  still  contain  amido-hydrogen,  they  readily  yield  imido- 
chlorides,  e.g.  CH3»CC1:N»C2H5,  ethyl  acetchioroimide. 

The  chlorine  in  these  compounds  is  chemically  active;  it 
can  be  exchanged  for  sulphur  or  for  an  amino  group. 

G.  Thiamides  and  Imido-thio-ethers 

Thiamides  are  compounds  derived  from  the  amides  by  the 
exchange  of  oxygen  for  sulphur,  e.g.  CHo'CS-NH2,  thiacet- 
amide  (ethane-thion-amide),  CH3-CS'NHC6H5,  thiacetanilide. 
They  are  mostly  crystalline  compounds,  and  result  from  the 
addition  of  H2S  to  the  nitriles  (CaJwurs),  e.g.: 

=  CH3.CS.NH2; 


by  treating  acid  amides  with  P2S5;  from  the  amido-chlorides, 
as  given  above;  and  by  the  action  of  H2S  or  CS2  upon  the 
amidines.  Both  simple  and  alkylated  thiamides  are  known. 

When  heated  alone,  they  yield  a  nitrile  and  sulphuretted 
hydrogen  (compare  Elimination  of  Water  from  Amides). 
When  hydrolysed  with  alkalis,  they  yield  the  corresponding 
acid,  ammonia  (amine)  and  H2S,  thus:  — 

K.CS-NHR  +  2H2o  =  K-CO-OH  +  H2s  +  NH2.R 

They  are  rather  more  acid  in  character  than  the  amides, 
and  thus  many  of  them  are  soluble  in  alkali  and  yield  metallic 
derivatives.  Consequently,  for  them,  as  well  as  for  the  amides, 

the  iso-formula  R-C-TT  is  taken  into  consideration.     From 


this  pseudo  form  R'C^Mtn  iso-thio  acid  amides,  are  derived 


a  number  of  compounds,  the  Imino-thio  -ethers,  by  the  re- 
placement of  one  or  both  the  hydrogen  atoms  by  alkyl  groups, 


AMtDlNttS  187 

acetimido-thiomethyl,  CH3.G<™HS;  methyl  iso-thio-acet- 

QI     /""'TIT  iN  £1. 

anilide,  CH3  •  C^-^  Q  j|  .     They  are  decomposed  by  hydro- 
chloric acid  into  esters  of  thiacetic  acid,  thus:  — 

CH3.qNH).SCH3-f  H20  =  CH3.CO.SCHS  +  NHg. 

These  imino-thio-ethers  are  prepared  by  the  action  of  mer- 
captans  upon  nitriles  in  presence  of  hydrochloric  acid  gas 
(Pinner),  and  by  the  action  of  alkyl  iodides  upon  thiaraides 
(Wallach,  Bernthsen)-. 


Imino-ethers,  R«C^-,,  which  are  the  oxygen  compounds 


corresponding  to  the  above  imino-thio-ethers,  and  which  are 
isomeric  with  the  alkylated  amides,  are  also  known  (Pinner), 
They  are  derived  from  the  pseudo  form  of  the  acid  amides, 


hypothetical    compounds    unknown    in   the    free 

state,  which  are  isomeric  with  the  simple  amides.  They  are 
formed  by  the  combination  of  a  nitrile  with  an  alcohol  under 
the  influence  of  hydrochloric  acid  gas,  and  in  certain  cases  by 
alkylating  amides;  some  of  them  are  liquids  which  boil  with- 
out decomposition,  but  others  are  only  known  in  the  form  of 
salts. 

H.  Amidines 

Amidinesare  compounds  derived  from  the  amides,  R-  CO  'NH2, 
R-CO-NHR',  and  R.CO-NR'2,  by  the  replacement  of  oxygen 
by  the  bivalent  imido-residue  NH  or  (NR)  : 


Acetamidine  (ethane-amidine)  Ethenyl-diphenyl  amidine. 

The  amidines  are  well-defined  crystalline  bases,  and  form 
stable  salts.  Like  all  acyl  derivatives,  they  are  readily  hydro- 
lysed,  and  thus  differ  from  the  amines. 

Formation.—  I.  By  heating  the  amides  with  amines  in  pre- 
sence of  PC13  (Hofmann)  : 

H2O. 


188  VIII.   POLYSYDRIC  ALCOHOLS 

2.  By  treating  the  imido-chlorides,  thiamides,  and  iso-thi- 
amides  with  ammonia  or  with  primary  or  secondary  amines 
(Wallach,  Bernthseri),  thus: — 

=  E-C(NH)(NHB')  +  H2S; 
=  R-C(NH)(NH2)  +  RSH. 

3.  By  heating  the  nitriles  with  (primary  or  secondary)  amine 
hydrochloride;  this  is  a  particularly  easy  method  when  aromatic 
amines  are  used,  but  not  in  the  case  of  ammonium  chloride 
(Bernthsen) : 

CH3.CN-f  NH2.R  =  CH3.C(NH)(NHR). 

4.  By  the  action  of  amine  bases  or  ammonia  upon  imino- 
ethers. 

Behaviour. — 1.  They  decompose  into  ammonia  or  amine  and 
acid  when  boiled  with  acids  or  alkalis  (see  above),  and  into 
ammonia  and  amide  upon  boiling  with  water. 

2.  The  dry  compounds,  when  heated,  readily  yield  am- 
monia or  amine  and  acid  nitrile,  so  long  as  the  imido-hydrogen 
atom  has  not  been  replaced  by  alkyl  groups. 

Amidoximes  are  the  compounds  formed  by  the  addition  of 
hydroxylamine  to  nitriles,  and,  from  this  mode  of  formation 
and  from  their  properties,  appear  to  be  amidines  in  which  an 
amido-  (imido-)  hydrogen  atom  is  replaced  by  hydroxyl: 

R.CN-f  NH2OH  =  R.C 

Such  an  amidoxime  is,  for  instance,  isuret,  NH2  •  CH :  N  •  OH, 
also  termed  methenyl  amidoxime,  which  is  prepared  from 
hydrocyanic  acid  and  hydroxylamine;  it  is  isomeric  with  carb- 
amide or  urea;  also  ethenyl  amidoxime,  CH3'C(N»OH)(NH2). 
These  compounds  are  hydrolysed  in  much  the  same  manner  as 
amidines. 


VIII.  POLYHYDRIC  ALCOHOLS 

A.  Dihydric  Alcohols  or  Glyeols,  CnH2n(OH)2 

The  dihydric  alcohols  may  be  regarded  as  derived  from  the 
paraffins  by  the  replacement  of  two  hydrogen  atoms  by  two 
hydroxyl  groups. 

As  the  monohydric  alcohols  are  often  compared  with  the 
hydroxides  derived  from  the  monovalent  jnetals,  we  may 


OLYCOLS  189 

compare  the  glycols  with  the  hydroxides  derived  from  the 
bivalent  metals,  e.g.  C2H4(OII)2  with  Pb(OH)2.  In  the  satu- 
rated dihydric  alcohols  we  have  the  hydroxyl  groups  attached 
to  a  bivalent  alkylene  radical,  e.g.  C2H4",  C3H0",  &c. 

In  many  respects  they  resemble  the  monohydric  alcohols, 
but  they  possess  these  properties  in  duplicate.  Just  as,  e.g., 
plumbous  hydroxide,  Pb(OH)2,  can  give  rise  to  two  series  of 
salts,  e.g.  the  basic  chloride,  OH-Pb-Cl,  and  the  normal 
chloride,  PbCl2,  so  glycol,  C2H4(OH)2,  can  give  rise  to  two 
chlorides,  OH«C2H4.C1  and  C2H4C12,  known  respectively  as 
glycol  monochlorhydrin  and  glycol  dichlorhydrin  or  ethylene 
dichloride.  Similarly,  with  the  acetates  and  amines  derived 
from  glycol  we  have — 

OH.C2H4.O.CO.CH3    and    C2H4(O.CO.CH3)2 

Mono-acetate  Di-acetate, 

OH.C2H4.NH2    and    C2H4(NH2) 

Hydroxyethylamine  Ethylene  diamine, 

and  similarly  with  other  glycols. 

The  glycols,  as  alcohols,  give  rise  to  every  class  of  alcoholic 
derivative;  but  when,  for  example,  the  formation  of  an  ester 
such  as  glycollic  monoacetate  has  taken  place,  this  still  behaves 
as  a  monohydric  alcohol,  yielding,  e.g.,  with  a  second  molecule 
of  acid,  a  new  ester;  it  is  therefore  termed  an  ester-alcohol. 

It  is  not  necessary  that  both  the  groups  which  replace 
the  hydrogen  or  hydroxyl  should  be  of  the  same  nature; 
thus  we  know  a  mixed  derivative  of  the  composition 
NH2  •  C2H4  •  S02  •  OH,  which  possesses  at  one  and  the  same 
time  the  character  of  an  amine  and  of  a  sulphonic  acid. 

The  glycols  are  mostly  thick  liquids  of  sweetish  taste,  a  few 
only  being  solid  crystalline  compounds;  they  dissolve  readily 
in  water  and  alcohol,  but  are  only  sparingly  soluble  in  ether. 
It  will  be  found  that  the  solubility  of  a  compound  in  water 
tends  to  increase,  and  its  solubility  in  ether  to  decrease,  with 
the  number  of  hydroxyl  groups  present  in  the  molecule  of  the 
compound.  Their  boiling-points  are  much  higher  than  those 
of  the  corresponding  monohydric  alcohols,  just  as  these  latter 
possess  considerably  higher  boiling-points  than  the  hydro- 
carbons from  which  they  are  derived. 

Constitution. — As  already  stated,  the  glycols  contain  two 
hydroxyl  groups  in  each  molecule;  the  arguments  in  favour 
of  the  presence  of  these  hydroxyl  groups  are  exactly  similar 
to  those  used  in  the  study  of  the  constitution  of  ethyl  alcohol, 


190  VIII.    POLYHYDRIC  ALCOHOLS 

and  are  btased  mainly  on  certain  methods  of  formation,  and  on 
the  chief  chemical  characteristics  of  the  compounds. 

Glycols  which  contain  two  hydroxyls  linked  to  the  same 
carbon  atom  are,  as  a  rule,  incapable  of  existence,  and  are 
only  known  in  derivatives  (see  p.  64).  Instead  of  the  glycols 
CH2(OH)2  and  CH3-CH(OH)2,  we  always  obtain  the  corre- 
sponding aldehydes,  CH2  :  0  and  CH3  •  CH  :  O.  All  glycols  con- 
tain their  hydroxyls  attached  to  two  different  carbon  atoms. 
Glycol  itself  has  thus  the  constitution  OH  •  CH2  •  CH2  •  OH, 
which  can  be  proved  directly  by  transforming  it,  by  means  of 
hydrochloric  acid,  into  glycol  chlorhydrin,  CH9C1  •  CH2  •  OH, 
and  oxidizing  the  latter  to  monochloracetic  acid,  Cll2Cl  •  CO  •  OH. 
In  this  last  compound  the  chlorine  and  hydroxyl  are  united  to 
different  carbon  atoms,  and  consequently  the  same  applies  to 
glycol  chlorhydrin  and  to  the  two  hydroxyl  groups  of  glycol. 
(Cf.  p.  62.) 

The  monohydric  alcohols  are  distinguished  as  primary, 
secondary,  and  tertiary.  The  glycols  may  in  the  same  way 
be  characterized  as  di-primary  when  they  contain  the  group 
CH2«OH  twice,  as  in  glycol;  as  primary-  secondary  when  they 
contain  the  group  CH2'OH  together  with  the  group  CH«OH, 
as  in  propylene  glycol,  CH3.CH(OH)  •  CH2OH;  further  as 
di-secondary,  primary-tertiary,  secondary-tertiary,  and  di- 
tertiary.  The  structure  of  a  glycol  is  usually  determined  by  an 
examination  of  its  oxidation  products.  (See  pp.  192,  203,  et  seq.) 

Modes  of  Formation.  —  1.  From  the  di-  halogen  -substituted 
derivatives  of  the  paraffins,  in  which  the  two  halogen  atoms  are 
attached  to  two  different  carbon  atoms,  e.g.  ethylene  bromide: 

(a)  By  transformation  into  the  di-acetates  by  means  of 
silver  or  potassium  acetate,  and  hydrolysis  of  the  ester  so 
produced  by  potash  or  baryta  water: 

CH2Br  •  CH2Br  -f  2  CH3  •  CO  •  O  Ag 

=  CH3.CO.O.CH2.CH2.O.CO.CH34-2AgBr, 


GH3.CO.O.CH2.CH2.0.(X).CH3 

=  OH.CH2.CH2-OH  +  2CH3.COOK. 

In  the  actual  preparation  of  glycol  from  ethylene  bromide, 
potassium  acetate  and  alcohol  (Demole),  this  saponification 
ensues  directly  upon  prolonged  boiling  of  the  mixture. 

(b)  By  boiling  with  water  and  lead  oxide  or  potassium 
carbonate.  These  reagents  serve  to  neutralize  the  acid  as  it 
is  formed,  and  so  the  reaction  is  facilitated: 

^-f  2HOH  ^  C2H4(OH)2  +  2HBr. 


PROPERTIES   OF  GLYCOLS  191 

2.  In  the  reduction  of  ketones  to  secondary  alcohols,  the 
so-called  pinacones,  i.e.  di-tertiary  glycols,  are  obtained  as  by- 
products (see  pp.  72  and  134),  thus:  — 

CMe2:0  CMe2.OH 

-f  2H  =    .  (pmacone). 

CMe2:O  CMe2.OH  * 

3.  By  the  careful  oxidation  of  olefines  by  means  of  very 
dilute  KMn04  (p..  45): 

CH2:CH2  +  O  +  H2O  =  OH.CH2.CH2.OH. 

Behaviour.  —  1.  As  in  the  case  of  the  monohydric  alcohols, 
the  hydrogen  of  the  hydroxylic  groups  is  directly  replaceable 
by  potassium  or  sodium,  with  the  formation  of  alcoholates,  e.g. 
OH  •  C2H4  •  ONa  and  C2H4(ONa)2,  sodium  and  di-sodium  glycols. 

2.  The  metal  in  these  compounds  may  be  exchanged  for 
new  alkyl  groups  by  treatment  with  alkyl  iodide,  when  gly- 
collic  ethers  are  obtained: 


C2H4(ONa)2  +  2C2H6I  = 

Glycol  di-ethyl  ether. 

These  ethers,  like  those  of  the  monohydric  alcohols,  are  stable, 
and  cannot  be  hydrolysed  by  dilute  mineral  acids  or  alkalis. 

3.  Acids  act  upon  them  to  produce  esters,  which  are  either 
normal  esters  or  ester-alcohols  (see  p.  189). 

The  halogen  esters  of  the  glycols  are  termed  chlor-,  brom-, 
or  iodhydrins,  e.g.  glycol  chlorhydrin,  C2H4C1(OH),  glycol  di- 
chlorhydrin,  C2H4C12,  &c.  The  ester-alcohols  which  are  formed 
by  the  action  of  halogen  hydride  may  also  be  regarded  as 
mono-substitution  products  of  the  monohydric  alcohols,  which 
cannot  be  prepared  by  direct  chlorination,  e.g.  C2H4C1(OH), 
monochlorethyl  alcohol.  Similarly  the  di-  halogen  esters, 
CHgCl-CHgCl,  CH2Br.CH2Br,  &c.,  are  the  di-substitution  pro- 
ducts of  the  paraffins,  viz.  ethylene  dichloride  and  dibromide. 

4.  As  the  halogen  atoms  in  the  chlor-,  brom-,  and  iodhy- 
drins are  readily  replaceable,  just  as  in   C2H5C1  or  C2H5I, 
these  compounds  may  be  used  for  the  preparation  of  most  of 
the  other  glycol  derivatives;  thus  they  yield  thio-glycols  with 
potassium  hydrosulphide,  amines  with  ammonia,  sulphonic  acids 
with  sodic  bisulphite,  and  nitriles  with  potassic  cyanide. 

5.  Alkalis  react  with  the  glycol  monochlorhydrins,  and  by 
the  elimination  of  HC1  yield  cyclic  anhydrides,  e.g.  ethylene 

PTT 

oxide,  •     2  J>0.    It  is  interesting  to  note  that  these  anhydrides 
CJBL/ 


192  VIII.   POLYHYDRIC  ALCOHOLS 

cannot  be  obtained  by  the  elimination  of  water  from  the  glycols 
themselves.  When  ethylene  glycol  is  heated  with  zinc  chloride 
at  230°  water  is  eliminated,  and  the  product  obtained  is  acet- 
aldehyde  (or  a  polymer).  This  reaction  is  explained  by  assum- 
ing the  intermediate  formation  of  unsaturated  alcohols  which 
are  not  in  themselves  capable  of  existence,  e.g.  CH2:CH(OH), 
but  which  immediately  undergo  transformation  into  the  iso- 
meric  aldehydes  or  ketones: 

CH2:CH.OH  =  CH3-CH:O. 

6.  As  alcohols  the  glycols  are  readily  oxidized.  If  they 
contain  the  primary  alcoholic  group,  they  can  yield  aldehydes 
and  acids  containing  the  same  number  of  carbon  atoms.  If  they 
contain  a  secondary  alcoholic  group,  they  yield  ketones,  e.g. : 

CH2OH.CH2OH  —  CHO.CH2OH 

and  —  COOH.CH2OH  —  COOH-COOH 

CH3.CH(OH).CH2OH  — >  CH3.CH(OH).COOH 

—  CH3.CO.COOH,  &c. 


Methylene-  and  Ethylidene-glycols.  (See  Aldehydes.) 
Ethylene  glycol  (glycol),  OH.CH2.CH2.OH  (Wurtz,  A.  100, 
110),  is  prepared  from  ethylene  bromide  by  means  of  potas- 
sium acetate  in  alcoholic  solution  (Demole),  or  of  potassium 
carbonate  in  aqueous  solution,  as  given  above  (A.  192,  250). 
For  properties,  see  above.  Its  formula  has  been  corroborated 
by  the  determination  of  its  vapour  density.  Oxidizing  agents 
transform  it  into  gly collie  acid,  OH  •  CH2  •  CO  •  OH,  and  oxalic 
acid,  OH- CO- CO- OH. 

Propylene  glycol  is  known  in  two  isomeric  forms,  viz. : 

(a)  Trimethylene  glycol,  /3-Propylene  glycol,  Propa7ie-l:3- 
diol,    OH-CHg.CH^.CHg.OH,   which   is   prepared    from   tri- 
methylene  bromide,  and  is  a  di-primary  glycol  boiling  at  216°. 
It  is  also  produced  by  the  Schizomycetes  fermentation  of  gly- 
cerol  (B.  14,  2270). 

(b)  a-Propylene  glycol,  Propane  - 1  :  2  -  diol,  CH3-CH(OH). 
CH2«OH,  can  be   prepared   from   propylene   bromide  in  an 
analogous  manner,  but  is  more  easily  obtained  by  distilling 
glycerol  with  caustic  soda.     It  boils  at  188°.     It  contains  an 
asymmetric  carbon  atom  in  the  molecule,  and  becomes  opti- 
cally (  — )  active  when  fermented,  i.e.  fission  fungi  destroy  the 
dextro  modification  more  rapidly  than  the  laevo. 


DERIVATIVES  OF  GLYCOLS  193 

Four  butylene  glycols,  and  various  amylene-  and  hexylene- 
glycols,  &c.,  are  also  known.  Of  these,  the  y-glycols  (in  which 
the  hydroxyls  are  in  the  positions  1:4,  and  which  therefore 
contain  the  grouping  •  G(OH)  •  C  •  C  •  C(OH)  •  )  yield  compounds 

of  the  furane  series  by  the  formation  of  anhydrides  (B.  22, 
2567),  and  therefore  stand  in  close  relation  to  thiophene  and 
pyrrole. 

Pinacone,  Tetramethyl  -  ethylene  glycol  (2:3-  Dimethyl  - 
butane-2:3-diol),  (CH3)2  :  C(OH)  •  C(OH)  :  (CH3)2.  The  hydrate, 
(+  6H20),  forms  large  quadratic  tables;  in  the  anhydrous 
state  it  is  a  crystalline  mass  melting  at  38°  and  boiling  at 
172°.  When  warmed  with  dilute  sulphuric  or  hydrochloric 
acid  it  yields  pinacoline,  CH3  •  CO  •  C(CH3)3,  methyl  tertiary- 
butyl  ketone  or  2:2-dimethyl-butan-3-one  (see  p.  137): 


In  this  reaction.  an  interesting  intramolecular  rearrangement 
occurs,  together  with  the  elimination  of  water. 

Numerous  other  pinacones  are  known.  They  may  be  ob- 
tained by  reducing  ketones  or  synthetically  (Lieben,  M.  17,  68; 
19,  16),  and  with  acids  yield  the  corresponding  pinacolines. 

DERIVATIVES  OF  THE  GLYCOLS 

The  ethers,  e.g.  C2H4(OCH3)2,  are  mostly  colourless  liquids 
with  ethereal  odours,  and  have  lower  boiling-points  than  the 
glycols.  (Cf.  Ether  and  Ethyl  Alcohol.)  They  cannot  be 
readily  hydrolysed. 

The  esters,  e.g.  C2H4(0  •  CO  •  CH8)2,  are  also  mostly  liquids, 
and  are  readily  hydrolysed. 

The  following  esters  of  inorganic  acids  are  interesting:  — 

Glycol  chlorhydrin,  CH2C1.CH2-OH,  obtained  by  passing 
hydrogen  chloride  into  warm  glycol,  or  by  the  addition  of 
hypochlorous  acid  to  ethylene,  is  a  liquid  miscible  with  water, 
and  boiling  at  130°;  in  this  last  respect  differing  from  its  corre- 
sponding alcohol  to  almost  the  same  extent  as  ethyl  chloride 
does  from  alcohol. 

Glycollic  di-nitrate,  CoH4(N08)2,  is  prepared  by  acting  on 
glycol  with  sulphuric  and  nitric  acids: 

C2H4(OH)2  +  2N02.OH  =  C2H4(0-N02)2  +  2H2O. 

It  is  a  yellowish  liquid,  insoluble  in  water,  is  readily  hydro- 

(3480)  N 


194  VIII.   POLYHYDRIO  ALCOHOLS 

lysed  by  alkalis  to  glycol  and  nitric  acid,  and  hence  the  con- 
stitution. The  formation  of  such  nitric  esters,  which  are 
highly  explosive,  is  characteristic  of  the  polyhydric  alcohols 
(see  Nitroglycerine). 

Ethylene  cyanide,  CN  •  CH2  •  CH2  •  ON,  obtained  by  the 
action  of  potassium  cyanide  on  ethylene  dibromide,  is  a 
crystalline  solid,  and  on  hydrolysis  with  alkalis  yields 
CO2H  •  CH2  •  CH2  •  C02H,  succinic  acid,  and  hence  may  be 
regarded  as  succinonitrile. 

Glycol  monochlorhydrin  with  potassium  cyanide  yields 
ethylene  cyanhydrin,  or  the  nitrile  of  /3-lactic  acid,  OH»CH2. 
CH2  •  CN.  Isomeric  with  it  is  ethylidene  cyanhydrin, 
CH3«CH(OH)«CN,  the  additive  product  of  hydrocyanic  acid 
and  aldehyde  (p.  126). 

Ethylene  oxide,  C2H40  (Wurtz\  obtained  by  distilling 
glycol  chlorhydrin  with  caustic  -potash  solution,  is  a  mobile 
liquid  of  ethereal  odour  boiling  at  13  -5°.  It  is  miscible  with 
water,  and  slowly  converted  into  the  glycol. 

It  has  many  of  the  properties  of  an  unsaturated  compound, 
e.g.  with  HC1  it  yields  the  chlorhydrin,  with  NH8  the  amino 
alcohol,  OH.CHg.CHg.NH^  and  with  chlorine  ethylene  di- 
chloride. 

It  is  largely  owing  to  the  last  reaction  that  the  ring  consti- 


s. 

tution,  i-.  /O,  and  not  the  open-chain  formula,  CH2:CH«OH, 
CHy 

is  given  to  the  compound.  The  formation  of  additive  com- 
pounds is  accompanied  by  the  rupture  of  the  ring.  Some  of 
the  higher  homologues  of  ethylene  oxide  are  much  more 
stable,  and  do  not  yield  additive  compounds;  this  is  due  to 
the  fact  that  the  ring  is  more  stable  and  therefore  less  easy  to 
rupture  (compare  Polymethylene  Compounds). 

AMINES  OF  THE  DIHYDRIO  ALCOHOLS 

These  are  derived  from  glycols  by  the  replacement  of  one  or 
both  hydroxyl  groups  by  amino  groups  : 

OH.CH2.CH2.NH2    and    NH2.CH2.CH2-NH2 

Hydroxy  ethylamine  Ethylene  diamine. 

In  the  former  case  compounds  are  obtained  wnich  possess 
the  properties  of  an  amine  in  addition  to  those  of  an  alcohol; 
in  the  latter,  diamines  free  from  oxygen,  which  are  analogous 
to  ethylamine,  but  are  di-acid  and  not  mono-acid  bases. 


DIAMINES  195 

Secondary  and  tertiary  diamines  corresponding  with  the 
primary  amiiie,  NH2-CH2.CH2.NH2,  are  known,  e.g.: 


The  methods  by  means  of  which  these  diamines  can  be 
obtained  are  analogous  to  those  described  for  the  monamines, 
viz.  :  — 

1.  By  heating  ethylene  bromide,  &c.,  with  alcoholic  am- 
monia to  100°  (Hofmanri): 

C2H4Br2  +  2NH3  =  C2H4(NH2)2  +  2HBr; 
C2H4(NH2)2  +  C2H4Br2  =  (C2H4)2N2H2  +  2HBr; 
(C2H4)2N2H2  +  C2H4Br2  =  (CgH^N,  +  2HBr. 


The  primary,  secondary,  and  tertiary  bases,  which  are  formed 
simultaneously,  can  be  separated  by  fractional  distillation. 

The  hydroxy  amines  (or  alkines,  Ladenburg)  are  obtained  in 
an  analogous  manner  by  using  ethylene  chlorhydrin,  thus:  — 

C2H4(OH)C1  -f  NH3 


In  this  case  also  primary,  secondary,  and  tertiary  bases  are 
produced  at  the  same  time,  and  are  separated  by  the  fractional 
crystallization  either  of  their  hydrochlorides  or  of  their  platini- 
chlorides. 

Ethylene  chlorhydrin  yields  choline  chloride  (p.  196)  with 
trimethylamine. 

2.  Primary  diamines  are  formed  by  the  reduction  of  the 
nitriles,  CnH2n(CN)a,  e.g.  by  adding  metallic  sodium  to  the 
hot  alcoholic  solution: 


CN.CH2.CH2.CN-f  8H 

Butylene  diaraine. 

Ethylene  diamine,  C2H4(NH2)2,  Diethylene  diamine, 
(C2H4)2N2H2,  &c.,  are  colourless  liquids  distilling  without  de- 
composition. The  former  boils  at  123°,  and  has  an  ammoni- 
acal  odour;  the  latter  melts  at  104°  and  boils  at  146°,  and 

is  identical  with  piperazine,  i.e.  hexahydro-pyrazine.     Hence 

/~ITT    r^TT 
it  possesses  the  constitutional  formula  NH<^QTT2  ^Tr^NH, 

and  has  a  closed-chain  constitution  (Hofmann,  B.  23,  3297). 

Tetr  amethylene  -  diamine,  Butane  -1:4-  diamine,  putrescine, 
butylene-diamine,  NH2  •  CH2  •  CH2  •  CH2  •  CH2  .  NH2,  is  prepared 
according  to  method  2,  and  is  also  formed  during  the  putre- 


196  VIII.    POLYHYDRIC   ALCOHOLS 


faction  of  flesh.  As  a  "  y-diamine  ",  i.e.  the  diamine  of  a 
y-glycol,  it  is  closely  related  to  pyrrole,  from  which  it  is 
formed  by  the  action  of  hydroxylamine  (whereby  a  dioxime 
is  first  produced),  and  subsequent  reduction  (B.  22,  1968). 

Pentamethylene  diamine,  cadaverine,  NH2»(CHA'NHo,  is 
formed  by  the  reduction  of  trimethylene  cyanide,  CN  •  (CH2)3  • 
CN,  which  on  its  part  is  prepared  from  trimethylene  bromide 
CH2Br.CH2.CH2Br,  and  KCN  (Ladenburg).  It  is  a  colourless 
syrupy  liquid  of  very  pronounced  spermaceti  and  piperidirie 
odour,  solidifies  in  the  cold,  and  boils  at  178°-179°.  It  possesses 
especial  interest,  because,  being  a  S-diamine,  it  gives  up  ammonia 

CH  •  CH 

and  yields  the  cyclic  base  piperidine,  C  ' 


(see  this). 

Many  of  these  poly  acid  bases  are  found  in  decaying  albumen 
and  in  corpses,  and  are  designated  ptomaines  or  toxines  (cf 
e.g.  B.  19,  2585). 

Choline,  bilineurine,  ethykl  -  trimethyl  -  ammonium  hydroxide, 
OH.CH2.CH2.NMe3.OH  (Strecker),  is  found  in  the  bile 
(x°^?>  bile),  brain,  yolk  of  egg,  &c.,  being  present  in  these 
combined  with  fatty  acids  and  gly  eery  1-  phosphoric  acid  as 
lecithin.  It  is  also  found  in  herring  brine,  hops,  beer,  and 
in  many  fungi,  &c.,  and  is  obtained  by  boiling  sinapine  with 
alkalis  (the  old  name  for  this  product  was  "  Sincaline  "). 
Choline  is  a  strong,  deliquescent  base,  and  readily  absorbs 
carbon  dioxide  from  the  air.  It  is  not  poisonous.  The 
chloride  has  the  formula  OH  'CoH^NMegCl.  Concentrated 
HN03  oxidizes  choline  to  muscarine,  C5H15N03  =  (OH)2CH- 
CH2  •  NMea  •  OH,  an  excessively  poisonous  base,  which  is 
present  in  toad-stool,  Agaricus  muscarius. 

By  transforming  choline,  by  means  of  hydriodic  acid,  into 
its  iodide,  CH2I-CH2'NMe3I,  and  treating  the  latter  with 
moist  oxide  of  silver,  and  also  from  the  putrefaction  of  choline, 
neurine  (vevpov,  nerve),  trimethyl  -vinyl  -ammonium  hydroxide, 
CH2:CH«NMe3-OH  (Hofmann),  is  obtained.  This  base,  con- 
taining the  unsaturated  radical  "  vinyl  ",  C2H3,  is  very  similar 
to  choline,  and  can  also  be  prepared  from  brain  substance;  it 
is  only  known  in  solution,  and  is  very  poisonous.  It  can  be 
re-transformed  into  choline.  (For  this,  and  also  for  deriva- 
tives, see  e.g.  A.  267,  249;  268.) 

Another  natural  compound  related  to  hydroxy  ethylamine 
is  taurine,  C2H7NS03  (Gmelin),  which  is  present  in  combina- 
tion with  choljc  acid  as  tauroeholic  acid  in  the  bile  of  oxen 


TRIHYDRIC  ALCOttOLS  19? 

and  many  other  animals,  also  in  the  kidneys,  lungs,  &c.  It 
crystallizes  in  large  monoclinic  prisms,  is  readily  soluble  in  hot 
water,  but  insoluble  in  alcohol,  and  decomposes  when  strongly 
heated.  Its  constitution  follows  from  its  synthesis. 

Isethionic  acid,  hydroxy-ethyl-sulphonic  acid,  OH •  GEL* 
CH2«S02»OH,  is  obtained  when  carbyl  sulphate,  C2H4S206 
(from  C2H4  and  S03),  is  boiled  with  water;  its  constitution 
follows  from  its  properties,  and  also  from  the  fact  that  it 
may  be  obtained  by  the  oxidation  of  the  hydroxymercaptan, 
OH-CH^CEL-SH.  Isethionic  acid  with  PC15  yields  the 
chloride  CH2C1  •  CH2  •  S02C1,  and  this  with  water  gives  chloro- 
ethyl-sulphonic  acid,  CH2C1  •  CH2  •  S02  •  OH,  which  with  am- 
monia yields  taurine;  its  constitution  must,  therefore,  be 
NH2.CH2.CH2-S02.OH,  amino-ethyl-sulphonic  acid,  and  in 
accordance  with  this  constitution  it  unites  in  itself  the  pro- 
perties of  an  alcoholic  amine  and  a  sulphonic  acid,  and  is 
therefore  at  the  same  time  a  base  and  an  acid.  It  forms 
unstable  salts  with  alkalis,  but  not  with  acids,  the  groups 
NH2  and  S03H  in  the  molecule  practically  neutralizing  one 
another,  so  that  its  reaction  is  neutral.  Nitrous  acid  converts 
it  into  isethionic  acid,  a  reaction  analogous  to  the  decom- 
position of  the  primary  amines  by  this  reagent.  As  an  alky  1 
sulphonic  acid,  it  is  not  hydrolysed  by  boiling  with  alkalis  and 
acids.  It  is  sometimes  represented  as  a  cyclic  ammonium  salt, 

CH2.NH3 
CH2-SO3. 

B.  Trihydric  Alcohols 

The  molecule  of  each  trihydric  alcohol  contains  three  hy- 
droxyl  groups,  each  attached  to  a  different  carbon  atom.  They 
may  be  regarded  as  analogous  to  the  hydroxides  of  tervalent 
meteU  e.g.  CSH6(OH)8  arid  A1(OH)3.  They  can  give  rise  to 
three  distinct  groups  of  derivatives  according  as  one,  two,  or 
three  of  the  hydroxyls  react,  e.g.  chlorides— C3H5C1(OH)2, 
monochlorhydrin;  C3H5C12-OH,  dichlorhydrin;  and  C3H5C13, 
trichlorhydrin  of  glycerol.  Similarly  for  acetates,  amino- 
derivatives,  &c. 

Although  the  compound  CH(OH)3,  ortho-formic  acid,  is  not 
known,  derivatives,  e.g.  ethyl  ortho-formate,  CH(OEt)3,  (p.  142), 
and  similarly  ethyl  ortho-acetate,  CH8-C(OEt)3,  can  readily  be 
prepared. 


19$  Vtlt.   fOLYHYDHIC  ALCOHOLS 

Glycerine,  glycerol,  propane-I:2:3-triol,  OH  •  CH2 .  CH(OH)  • 
CH2-OH.  (Scheek,  1779;  formula  established  by  Pelouze  in 
1836,  and  constitution  by  Berthelot  and  Wurtz.) 

Synthesis. — By  heating  1 : 2 : 3-trichlorpropane  with  water  tc 
170°: 

CH2C1  CH2.OH 

CHC1  +3H-OH  =  CH-OH  +  3HC1. 
CH2C1  CH2.OH 

The  trichlorpropane  is  itself  obtainable  from  isopropyl  iodide 
(which  can  also  be  prepared  synthetically)  by  conversion  into 
propylene,  addition  of  C12,  and  heating  the  propylene  dichloride 
thus  formed  with  iodine  chloride  (Friedel  and  Silva,  Bull.  Soc. 
Chim.  20,  98): 

CH3.CHI.CH3  —  CH3.CH:CH2 

—  CH3.CHC1-CH2C1  —  CH2C1.CHC1.CH2C1. 

Glycerol  is  also  produced  when  allyl  alcohol  is  oxidized  with 
very  dilute  potassium  permanganate : 

CH2:CH-CH2.OH  —  OH.CH2.CH(OH).CH2.OH. 

The  constitution  of  glycerol  follows  from  these  syntheses  and 
also  from  its  relation  to  tartronic  acid  (p.  199);  each  of  the 
three  hydroxyls  is  attached  to  a  separate  carbon  atom. 

Preparation. — Glycerol  is  usually  prepared  by  hydrolysing 
the  natural  fats  and  oils  (especially  olive-oil),  which  are  the 
glyceryl  salts  of  fatty  and  other  acids  (p.  158).  The  hydro- 
lysis may  be  effected  by  means  of  superheated  steam,  by 
heating  with  lime  and  water,  or  with  sulphuric  acid.  They 
are  thus  resolved  into  their  components,  glycerol  and  acid; 
the  glycerol  distils  over  with  the  superheated  steam,  and  may 
be  purified  by  animal  charcoal.  Hydrolysis  by  means  of  an 
enzyme  contained  in  castor-oil  seeds  is  used  commercially. 

In  the  manufacture  of  stearic  acid  (p.  161)  the  fats  are 
hydrolysed  with  sulphuric  acid,  when  the  glycerol  is  con- 
verted into  glyceryl-sulphuric  acid,  C3H5(OH)2(0*S03H),  from 
which  it  can  be  obtained  by  boiling  with  water  or  with  lime. 
In  the  preparation  of  plaister,  by  boiling  fats  with  lead  oxide 
and  water  (p.  160),  an  aqueous  solution  of  glycerol  is  obtained 
together  with  the  insoluble  lead  plaister. 

Large  quantities  of  glycerol  are  now  recovered  from  the 
liquors  from  which  the  hard  soaps  (p.  158)  have  separated. 

Properties. — It  is  a  thick,  colourless  syrup,  of  specific  gravity 


GLYCEROL  199 

1-27,  solidifies,  when  strongly  cooled,  to  crystals  like  those  of 
sugar-candy,  which  melt  at  17°.  It  boils  at  290°,  but,  when 
impure,  can  be  distilled  without  decomposition  under  diminished 
pressure  only,  viz.  at  170°  under  12  mm.  It  is  very  hygro- 
scopic, and  mixes  with  water  and  alcohol  in  all  proportions, 
but  is  insoluble  in  ether. 

Uses. — In  the  manufacture  of  liqueurs,  fruit  preserves,  wine, 
&c.;  for  non-drying  stamp  colours  and  blacking;  when  mixed 
with  glue,  in  book  printing;  as  a  healing  ointment  for  external 
use;  but  especially  in  the  manufacture  of  nitro-glycerine  and 
in  the  colour  industry. 

Behaviour. — 1.  With  alkalis  and  other  metallic  hydroxides 
it  forms  alcoholates,  which  are  readily  decomposed  again  into 
their  components. 

2.  As  a  trihydric  alcohol  the  hydrogen  atoms  of  the  OH 
groups  can  be  replaced  by  alkyl  radicals  yielding  ethers,  e.g. 
mono-ethylin,  C3H5(OH)2(OC2H5),and  triethylin,  C3H5(OC2H5)3, 
liquids  which  boil  without  decomposition. 

3.  As  an  alcohol  it  forms  the  most  various  esters :  thus,  with 
sulphuric  acid,  the  easily  saponifiable  glyceryl-sulphuric  acid, 
C3H5(OH)2(0  •  S03H);  with  phosphoric  acid,  glyceryl-phosphoric 
acid,  C3H5(OH)2(O.P03H2);  with  nitric  acid,  glyceryl  trini- 
trate,  C3H^(0'N02)3;  with  hydrochloric  acid  the  chlornydrins ; 
and  with  the  higher  fatty  acids  the  fats.     For  its  behaviour 
with  hydriodic  acid,  or  iodine  and  phosphorus,  see  p.  60. 

4.  It  yields  compounds  of  a  mercaptan  or  aminic  character 
by  exchange  of  OH  for  SlTor  NH2. 

5.  When  distilled  with  dehydrating  agents,  e.g.  phosphorus 
pentoxide,  or,  better,  anhydrous  potassium  hydrogen  sulphate, 
two  molecules  of  water  are  eliminated  from  each  molecule  of 
glycerol,  and  acrolein  (p.  130)  is  formed.    By  the  indirect  sepa- 
ration of  one  mol.  H20,  glycide  alcohol,  C3H602,  is  obtained. 

6.  Oxidizing  agents  convert  it,  according  to  circumstances, 
either   into   glyceric,   OH  •  CH2 .  CH(OH) .  C025,  tartronic, 
C02H.CH(OH).C02H,  or  mesoxalic  acid,  C02JB^  CO .  CO  JEt, 
or  acids  with  a  smaller  number  of  carbon  atoms.     The  for- 
mation  of   the   three   above-mentioned   acids   indicates   that 
glycerol  molecule  must  be  built  up  of  two  primary  and  one 
secondary   alcoholic  groups,  as   represented   in   the  formula 
already  given.     Halogens  oxidize  and  do  not  substitute. 

7.  It  yields 'normal  butyl  alcohol,  caproic  acid,  and  butyric 
acid  by  certain  fermentations.     (Cf.  B.  16^  884.) 

8.  It  is  largely  used  in  the  preparation  of  allyl  alcohol  (p.  82), 


200  VIII.  POLYttYDRIC  ALCOHOLS 

acrolein  (p.  130),  allyl  iodide  (p.  65),  isopropyl  iodide  (p.  60), 
and  formic  acid  (p.  148). 

DERIVATIVES 

Chlorhydrins  (hydrochloric  esters).  Mono-  and  dichlor- 
hy  drills  are  formed  by  the  action  of  hydrochloric  acid  on 
glycerol,  and  trichlorhydrin  by  the  action  of  phosphorus 
pentachloride  on  the  mono-  or  di-compounds.  Each  of  the 
two  first-named  exists  in  two  isomeric  modifications. 

a-Monochlorhydrin,  S-Chloro-propane-l-.Z-diol,  CH2(OH)' 
CH(OH).CH2C1,  is  formed  from  epichlorhydrin,  C3H5O.C1, 
(see  below),  and  water;  a-dichlorhydrin,  I:3-dichloro-propane-2-ol, 
CH2C1  •  CH(OH)  .  CH2C1,  from  epichlorhydrin  and  HC1;  /3-mono- 
chlorhydrin,  CH2(OH).CHC1-CH2(OH),  and  ^-dichlorhydrin, 
CH2C1.CHC1-CH2.OH,  by  the  addition  of  hypochlorous  acid 
to  allyl  alcohol  or  to  allyl  chloride. 

The  chlorhydrins  are  liquids  sparingly  soluble  in  water,  and 
readily  soluble  in  alcohol  and  ether.  Their  boiling-points  are 
much  below  that  of  glycerol. 

Glycide  Compounds.  —  By  the  elimination  of  water  from 
glycerol  a  compound  is  obtained  which  unites  within  itself 
the  properties  of  ethylene  oxide  and  of  a  monohydric  alcohol, 
viz.  glycide  alcohol, 

OH-CHjj.CH.OH  OH.CH2.CH\ 

CHj-OH    "  CH2/' 

which  is  isomeric  with  propionic  acid. 

It  may  be  prepared  by  the  abstraction  of  HC1  from  a-mono- 
chlorhydrin  by  means  of  baryta,  just  as  ethylene  chlorhydrin 
yields  ethylene  oxide.  It  is  a  colourless  liquid,  boiling  at  162°, 
and  miscible  with  water,  alcohol,  and  ether.  It  combines  with 
H20,  yielding  glycerol,  and  with  HC1  yielding  the  chlorhydrin, 
and,  as  an  alcohol,  forms  esters  (glycide  esters),  &c.  Its  hydro- 
chloric ester  is  epichlorhydrin, 

CH2C1- 


isomeric  with  chlor-acetone  and  propiony)  chloride,  a  mobile 
liquid  of  chloroform  odour,  boiling  at  117°,  which  is  formed  by 
the  elimination  of  HC1  from  either  of  the  dichlorhydrins.    Like 
ethylene  oxide  it  is  capable  of  combining  with  ELO,  HC1,  &c. 
Esters  of  Nitric  Acid.—  Mononitrin,  C3H6(OH)2(O  • 


POLYHYDRIC  ALCOHOLS  201 

and  trinitrin  or  nitre-glycerine,  C3H5(0'N02)3,  are  known. 
The  latter  is  prepared  by  treating  glycerol  with  a  cold  mix- 
ture of  concentrated  nitric  and  sulphuric  acids  (B.  1899,  32, 
1444).  It  is  a  colourless  oil,  insoluble  in  water,  poisonous, 
and  of  a  sweet,  burning,  aromatic  taste.  Sp.  gr.  1*6.  M.-pt. 
about  11°-12°.  It  burns  without  explosion,  but  explodes  with 
terrible  violence  when  quickly  heated  or  when  struck  (Nulel's 
explosive  oil).  When  mixed  with  kieselguhr  in  the  proportion 
of  three  parts  to  one  it  forms  dynamite  (Nobel,  1867),  which 
is  exploded  by  fulminate  of  mercury  with  frightful  force.  It 
is  hydrolysed  by  alkalis  and  by  ammonium  sulphide,  yielding 

glycerol  and  nitric  acid,  and  hence  its  constitution  as  a  nitrate, 
3H5(0  •  N02)3,  and  not  a  nitro-derivative,  e.g.  C3H2(N02)3(OH)3. 

The  esters  derived  from  glycerol  and  the  fatty  acids  are 
largely  met  with  in  vegetable  and  animal  oils  and  fats.  Most 
of  these  are  the  normal  esters,  e.g.  glyceryl  tripalmitate,  tripal- 
mitin,  C3H5(0 •  CO •  C15H31)3,  tristearin,  &c.  (see  p.  158,  et  seq.). 

These  esters  can  also  be  obtained  artificially,  as  can  also  the 
mono-  arid  dihydric  esters,  e.g.  monopalmitin,  (OH)2C3H5.O 
CO.C15H31,  and  dipalmitin,  OH . C3H5(0 •  CO •  C15H31)2. 

Most  are  wax-like  solids,  and,  on  hydrolysis,  yield  as  ulti- 
mate products  glycerol  and  the  fatty  acid.  With  the  normal 
esters  this  hydrolysis  occurs  in  stages  yielding  the  mono- 
hydroxy  ester,  then  the  dihydroxy,  and  finally  glycerol. 

C.  Tetra-,  Penta-,  and  Hexahydric  Alcohols 

These  alcohols  can  react  respectively  with  4,  5,  or  6  mole- 
cules of  a  monobasic  acid  to  form  neutral  esters,  and  conse- 
quently 4,  5,  or  6  alcoholic  hydroxyls  are  to  be  assumed  as 
present  in  their  molecules. 

The  number  of  hydroxyls  present  in  an  alcohol  is  usually 

determined  from  the  number  of  acetyl  groups  present  in  the 

ester  which  is  formed  when  the  alcohol  is  heated  with  acetic 

anhydride  and  anhydrous  sodic  acetate,  thus:— 

C6H8(OH)6  +  6(CH3.CO)20  =  C6H8(0-CO.CH3)6+  6CH..CO.H. 

One  of  the  simplest  methods  of  determining  the  number  of 
acetyl  groups  is  to  hydrolyse  the  acetate  by  distilling  with  ben- 
zene sulphonic  acid  in  steam,  and  to  titrate  the  acetic  acid  in 
the  distillate  with  standard  barium  hydroxide,  using  phenol- 
phthalein  as  indicator  (Sudborough  and  Thomas,  J.  C.  S.  1905, 
1752). 


202  VIII.   POLYHYDRIC  ALCOHOLS 

The  ester  of  any  alcohol  in  question  may  also  be  prepared  by 
the  aid  of  an  acid  containing  halogen,  bromo-benzoic  acid  being 
especially  suitable  for  this;  and  from  the  percentage  of  bromine 
found  in  the  ester,  the  number  of  acid  radicals  which  have  entered 
the  molecule,  i.e.  the  number  of  hydroxyls,  can  be  deduced. 

The  polyhydric  alcohols  are  solid  crystalline  compounds  of 
sweet  taste.  Many  occur  as  natural  products,  and  they  may 
be  obtained  by  the  reduction  of  the  corresponding  hydroxy 
aldehydes,  hydroxy  ketones,  or  hydroxy  monobasic  acids  (man- 
nonic  acid,  &c.)  by  sodium  amalgam.  (E.  Fischer,  B.  22,  2204.) 
Conversely,  cautious  oxidation  by  bromine  water  transforms 
them  first  into  sugars  (hydroxy  aldehydes),  and  then  into  the 
corresponding  acids.  As  a  rule  they  cannot  be  volatilized 
without  decomposition.  Their  derivatives  are  exactly  analo- 
gous to  those  of  glycol  and  glycerol. 

Their  constitution  follows  from  the  generalization  already 
repeatedly  referred  to,  viz.  that  not  more  than  one  hydroxyl 
group  can  be  attached  to  the  same  carbon  atom  without  the 
immediate  separation  of  water,  so  that  a  tetrahydric  alcohol 
must  contain  at  least  4,  and  a  hexahydric  alcohol  at  least  6, 
atoms  of  carbon.  The  tetrahydric  alcohol  erythritol,  C4H6(OH)4, 
has  thus  the  formula: 

OH  •  CH2  •  CH(OH)  •  CH(OH)  •  CH2  •  OH, 

and  mannitol,  the  simplest  of  the  hexahydric  alcohols,  C6H8(OH)6, 
the  formula: 

OH.CH2(CH.OH)4.CH2.OH. 

All  the  common  polyhydric  alcohols  have  a  normal  carbon 
chain,  as  on  reduction  with  hydriodic  acid  they  yield  normal 
secondary  iodides,  e.g.  erythritol  yields  2-iodo-butane,  CH3- 
CHI.CH2.CH3. 

1.  Tetrahydric  Alcohols.— Ortho-carbonic  ether,  C(OC2HJ4, 
is  to  be  regarded  as  the  ether  of  the  hypothetical  alcohol,  C(OH)4, 
which  may  be  looked  upon  as  the  hydrate  of  carbonic  acid, 
but  is  itself  incapable  of  existence.     It  is  a  liquid  of  ethereal 
odour,  boiling  at  159°. 

Erythritol  (Butane-tetrol)  occurs  in  the  free  state  in  Proto- 
coccus  vulgaris,  and  combined  with  orsellinic  acid  as  an  ester 
(erythrin),  in  many  lichens  and  algas.  It  forms  large  quad- 
ratic crystals,  sparingly  soluble  in  alcohol  arid  insoluble  in 
ether.  M.-pt.  112°;  b.-pt.  about  300°. 

2.  Pentahydric  Alcohols,  Arabitol,  OH .  CH2 .  (CH  -  OH)3 . 


HEXAHYD&IC  ALCOttOLS  203 

CH2«OH  (from  arabinose  by  reduction).  Xylitol,  by  the 
reduction  of  xylose,  is  stereo  -  isomeric ;  and  rhamnitol, 
OH  •  CH2  •  (CH .  OH)4 .  CH8,  m.-pt.  121°,  from  rhamnose,  is 
homologous. 

3.  Hexahydric  Alcohols,— Mannitol,  OH.CH2.(CH.OH)4. 
CH2»OH  (Proust,  1800),  is  found  in  many  plants,  for  instance 
in  the  larch,  in  Viburnum  Opulus,  in  celery,  in  the  leaves  of 
Syringa  vulgaris,  in  sugar-cane,  in  Agaricus  integer  (of  the  dry 
substance  of  which  it  forms  20  per  cent),  in  rye  bread,  and 
especially  in  the  manna  ash,  Fraxinus  ornus,  the  dried  juice 
of  which  constitutes  manna.  It  can  be  prepared  from  grape- 
sugar,  or  still  better  from  fruit  sugar,  from  which  it  only 
differs  in  composition  by  containing  two  atoms  of  hydrogen 
more  in  the  molecule,  by  reduction  with  sodium  amalgam. 

It  crystallizes  in  fine  needles  or  rhombic  prisms,  and  is 
readily  soluble  in  cold  water  and  boiling  alcohol.  It  is 
dextro-rotatory,  but  a  laevo-rotatory  and  an  inactive  modi- 
fication are  also  known.  (See  Mannonic  Acid.)  M.-pt.  166°. 
When  heated  it  is  converted  into  its  anhydrides,  mannitan, 
C6H1205,  and  mannide,  C6H1004.  Cautious  oxidation  converts 
mannitol  into  a  mixture  of  mannose,  OH  •  CH2(CH  •  OH)4  •  CHO, 
and  fructose,  OH.CH2(CH.OH)3.CO.CH2.OH.  Nitric  acid 
oxidizes  it  to  saccharic  acid,  C02H .  (CH  •  OH)4  •  COJE ;  hydri- 
odic  reduces  it  to  secondary  hexyl  iodide,  CH3  •  CHI  •  (CH2)3  • 
CH8  (p.  59). 

The  molecule  of  mannitol  contains  4  asymmetric  carbon 
atoms,  e.g. : 

OH.CH2.CH(OH).CH(OH).CH(OH).OH(OH).CH2OH, 

and  hence  a  number  of  stereo-isomerides  are  known,  e.g.  d-,  1-, 
and  r-mannitol,  d-,  1-,  ?--sorbitol,  and  dulcitol,  which  is  optically 
inactive  owing  to  the  fact  that  its  molecule  is  symmetrical  in 
configuration.  (See  Stereochemistry  of  the  Sugars.) 

The  sugars  are  closely  related  to  the  penta-  and  hexa- 
hydric  alcohols,  being  the  corresponding  polyhydric  aldehydes 
or  ketones.  The  alcohols  as  a  rule  are  not  fermented  by 
yeast,  and  do  not  reduce  an  alkaline  cupric  solution,  dulcitol 
excepted. 
OXIDATION  PRODUCTS  OF  THE  POLYHYDRIC  ALCOHOLS 

Just  as  the  monohydric  alcohols  are  oxidized  to  aldehydes, 
ketones,  and  acids,  so  the  polyhydric  alcohols  pass,  on  oxida- 
tion, into  aldehydes,  ketones,  and  polybasic  acids. 


204 


VIII.   POLYHYDRIC  ALCOHOLS 


Further,  by  this  oxidation  of  the  polyhydric  alcohols  we 
obtain  not  only  aldehydes,  ketones,  and  acids,  but  also 
numerous  compounds  which  possess  a  double  chemical  char- 
acter in  so  far  as  they  unite  in  themselves  the  properties  of 
more  than  one  of  these  classes  of  compounds.  These  are  the 
hydroxy  aldehydes,  which  are  at  the  same  time  aldehyde  and 
alcohol,  the  hydroxy  ketones,  at  the  same  time  ketone  and 
alcohol,  the  hydroxy  acids,  aldehyde  acids,  ketone  acids,  and 
ketone  aldehydes. 

An  aldehyde  acid,  for  instance,  is  capable,  as  an  acid,  of 
forming  salts,  esters,  and  amides  on  the  one  hand;  and  on  the 
other,  as  an  aldehyde,  it  is  able  to  reduce  an  ammoniacal 
silver  solution,  to  combine  with  NaHS03,  and  to  react  with 
hydroxylamine,  &c. 


SUMMARY  OF  THE  OXIDATION   PRODUCTS 
(a)  Of  the  di-primary  alcohols. 
CHO 


CH2-OH 

CH2-OH 
Glycol 


CH2-OH 

"^CHO 

Glycollic  aldehyde 


CHO 

Glyoxal 


CH2-OH 
CO-OH 

Glycollic  acid 


^  CHO 

*  CO-OH^ 

Glyoxalic  acid. 


CO- OH 
CO-OH 

Oxalic  acid 


Possible    products:    Di-aldehydes,    dibasic   acids,    hydroxy 
aldehydes,  hydroxy  acids,  aldehyde  acids. 

(b)  Of  the  hydroxy  primary-secondary  alcohols. 


CH, 


Methyl-glyoxal 


CH2-OH 

•-Propylene 
glycol 


CH-OH    - 
CHO 

(Lactic  aldehyde, 
unknown) 


CH3 
CH-OH 
CO- OH 

Lactic  acid 


CO-  OH 


.=0° 


If 

I! 


MONOHYDROXY  FATTY  ACIDS  205 

Possible  products:  hydroxy  aldehydes,  hydroxy  ketones, 
ketone  aldehydes,  hydroxy  acids,  ketone  acids. 

(c)  Of  the  di-secondary  alcohols:  hydroxy  ketones,  di- 
ketones.  (No  dibasic  acids  or  alcohol  acids,  Cn.)  e.g. : 


CHg-CH-OH  CH3.CH.OH  CH3.CO 

CH3.CH.OH    "    "    CH3.CO  '    CH3.CO 

Di-secoudary  butylene  glycol       Dimethyl-ketol  Di-acetyl. 

(d)  The  tri-  and  polyhydric  alcohols  are  capable  of  yielding 
the  most  various  products  upon  oxidation,  especially  poly- 
hydroxy  ketones,  polyhydroxy  acids,  keto-acids,  and  polybasic 
acids. 

Of  all  these  oxidation  products,  the  most  important  are  the 
hydroxy  acids,  the  polybasic  acids,  and  the  keto-acids.  For 
the  sake  of  convenience  the  hydroxy  monobasic  acids  will  be 
treated  of  first. 


IX.  HYDROXY  MONOBASIC  ACIDS  AND  COM- 
POUNDS RELATED  TO  THEM 

A.  Monohydroxy  Fatty  Acids 

These  compounds  may  be  regarded  as  monohydroxy  deri- 
vatives of  the  fatty  acids,  e.g.  OH-CHg-COnH,  hydroxy  acetic 
acid,  or  glycollic  acid,  OH  •  CH2  •  CH2  •  C02H,  ^-hydroxy  pro- 
pionic  acid,  or  /2-lactic  acid,  &c. 

They  combine  within  themselves  the  properties  of  a  mono- 
basic acid  and  of  an  alcohol,  and  are  consequently  capable 
of  forming  derivatives  as  alcohols,  as  acids,  and  as  both 
together. 

The  lowest  members  of  the  series,  which  are  the  most  im- 
portant, are  glycollic  acid  and  lactic  acid,  both  syrupy  liquids 
which  solidify  to  crystalline  masses  in  the  desiccator,  and  readily 
give  up  water  to  form  anhydrides.  They  cannot  be  volatilized 
without  decomposition;  and  are  readily  soluble  in  water,  and 
for  the  most  part  also  in  alcohol  and  ether. 

Formation. — 1.  By  the  regulated  oxidation  of  the  glycols. 
(See  Summary,  p.  204.) 

2.  From  the  fatty  acids,  through  their  monohaloid  substi- 
tution products,  the  halogen  of  these  being  easily  replaced  by 


206  IX.  HTDROXY  MONOBASIC  ACIDS 

hydroxyl,  either  by  means  of  moist  oxide  of  silver  or  often  by 
prolonged  boiling  with  water  alone: 

CH2C1.C02H  +  H20  =  CH,(OH).C02H 


This  reaction  is  conditioned  by  the  halogen  having  the 
a-position  with  respect  to  the  carboxyl  (cf.  pp.  169  and  170). 

For  a  reaction  of  these  haloid-substitution  products  in  a 
different  direction,  see  fi-  and  y-hydroxy  acids. 

3.  From  the  aldehydes  and  ketones  containing  1  atom  of 
carbon  less,  by  the  preparation  of  their  hydrocyanic  acid  com- 
pounds, cyanhydrins  (see  pp.  126  and  135),  and  hydrolysis 
of  the  latter.  Thus,  irom  aldehyde  is  produced  ethylidene 
cyanhydrin,  and  from  this  a-lactic  acid: 


CH3.CH(OHXCN)  +  2H20  =  CH3.CH(OH).CO2H  +  NH3. 

Since  the  aldehydes  and  ketones  are  easily  obtained  from 
the  corresponding  alcohols,  this  reaction  furnishes  a  means  of 
preparing  the  acids,  CnH2n(OH)  (C03H),  from  the  alcohols, 
CnH3n+l(OH),  i.e.  of  introducing  carboxyl  into  the  latter  in 
place  of  hydrogen;  this  is  a  most  important  synthesis. 

4.  From  the   glycollic  cyanhydrins   by  saponification,  e.g. 
/2-lactic  acid  from  ethylene  cyanhydrin: 

OH.CH2.CH2.CN  +  2H20  =  OH-CH^CHa-CO.^  -f  NH3. 

As  the  cyanhydrins  can  be  readily  obtained  from  the  glycols 
(p.  191),  this  formation  of  hydroxy  acids  represents  an  exchange 
of  a  hydroxyl  of  the  glycol  for  carboxyl,  and  is  analogous  to 
the  formation  of  acetic  acid  from  methyl  alcohol.  Thus  :  — 

OH.CH2.CH2-OH  —  OH-CH2.CHoCl 

—  OH.CH2-CH2.CN  —  OH.CH2.CH2.C02H 

and  CHj-OH  —  CH3C1  —  CH3.CN  —  CH3.CO2H. 

5.  By  the  reduction  of  aldehyde  acids  or  ketonic  acids,  e.g. 
lactic  from  pyruvic  acid  (p.  225).     This  reaction  corresponds 
with  the  formation  of   the  alcohols   from  the  aldehydes  or 
ketones  by  reduction. 

6.  By  the  action  of  nitrous  acid  upon  amino  acids  (see  Gly- 
cocoll);  a  reaction  analogous  to  the  formation  of  alcohols  from 
amines  (p.  108). 

7.  Hydroxy  acids  of  the  fatty  series  containing  an  equa] 
number  of  carbon  atoms  result  by  direct  oxidation,  if  a  CH 


NOMENCLATURE  OF  HYDROXY  ACIDS        207 

group,  i.e.  a  "tertiary"  hydrogen   atom,  is  present  in  the 
original  acid  (E.  Meyer,  B.  11,  1283;  12,  2238): 


(CH3)2CH.C02H 

laobutyric  acid  a-Hydroxy-isobutyric  acid. 

Constitution  and  Isomers.  —  As  hydroxy  compounds  of  the 
fatty  acids,  the  acids  of  the  foregoing  series  can  exist  in  as 
many  modifications  as  the  monohaloid  fatty  acids.  Thus  there 
is  only  one  glycollic  acid,  corresponding  with  monochloracetic 
acid,  but  two  lactic  acids  —  corresponding  with  a-  and  /2-chloro- 
propionic  acids  —  are  possible,  and  both  actually  exist;  they 
are  designated  as  a-  and  /3-hydroxy  propionic  acids: 


O^  (a-chloro-propionic  acid). 
CH3»CH(OH)-CO^[  (a-hydroxy  -propionic  acid  or  common  lactic 

acid). 

CH2I«CH2-CO2H  (/3-iodo-propionic  acid). 
OH-CH2-CH2-CO2H  (jS-hydroxy  propionic  acid  or  /3-lactic  acid) 

From  the  two  butyric  acids  can  be  theoretically  derived: 

(a)  From  the  normal  acid: 

CH3.CH2.CH2.CO2H, 

y        ft 

an  a-,  ft-,  and  y-hydroxy  butyric  acid. 

(b)  From  isobutyric  acid  : 


an  a-  and  /3-hydroxy  isobutyric  acid. 

Systematic  Nomenclature.—  OH  .  CH2  •  CH2  •  C02H,  Propane-3- 
jlrl-acid;  (CH3)2  •  C(OH)  •  C02H,  2  -Methyl-propane-  2  -ol-l-add] 
OH.CH2.CH2.CH2.C02H,  Butane4-ol-\-add,  &c. 

The  constitution  of  these  hydroxy  acids  can  often  be  deduced 
from  their  methods  of  formation.  Thus  the  preparation  of 
common  lactic  acid  from  aldehyde,  CH3-CHO,  according  to 
method  3,  shows  that  it  contains  the  group  CH3-CH:,  "ethy- 
lidene";  it  is  therefore  termed  "ethylidene  lactic  acid"  On 
the  other  hand,  the  formation  of  /3-hydroxy  propionic  acid 
from  glycol  cyanhydrin,  according  to  4,  is  a  proof  of  its  con- 
taining the  group  .CH2.CH2.,  "ethylene";  hence  the  name 
"ethylene  lactic  acid". 

The  constitution  can  also  frequently  be  deduced  from  a 
study  of  their  oxidation  products;  if  they  can  be  oxidized, 
for  instance,  to  dibasic  acids  (which  contain  two  carboxyls), 


208  IX.    HYDROXY  MONOBASIC  ACIDS 

then  they  must  contain  a  primary  alcohol  group,  •  CH2  •  OH, 
since  only  such  a  group  yields  a  new  carboxyl  on  oxidation. 
Ethylene  lactic  acid  is  therefore  a  "primary"  alcohol  acid. 
Its  isomer,  ethylidene  lactic  acid,  is  similarly  a  "secondary" 
alcohol  acid,  while  a-hydroxy  isobutyric  acid  is  a  "  tertiary 
alcohol  acid,  i.e.  acid  and  tertiary  alcohol  at  the  same  time. 

Behaviour. — 1.  The  double  chemical  character  of  the  hydroxy 
acids  will  be  dealt  with  more  in  detail  under  Glycollic  Acid. 
As  acids  they  form  salts,  esters,  and  amides;  as  alcohols  they 
yield  ethers,  amines,  &c.  Of  these  derivatives  the  alcoholic 
amines  of  the  acids,  the  so-called  amino  acids,  are  of  especial 
interest.  (See  Glycocoll,  p.  211.) 

2.  The  hydroxy  acids  form  different  kinds  of  anhydrides, 
viz.:  (a)  as  alcohols  (see  Di-glycollic  Acid);  (b)  one  molecule 
as  alcohol  forms  with  a  second  molecule  as  acid  an  ester,  with 
elimination  of  H20  (see  Glycollic  Anhydride);  (c)  operation  b 
is  repeated,  the  first  molecule  acting  as  acid,  and  the  second 
as  alcohol  (see  Glycolide);  (d)  one  molecule  loses  H20,  with 
formation  of  an  "  intramolecular  "  anhydride,  a  so-called  ladone 
(see  p.  217). 

3.  For  behaviour  upon  oxidation  see  p.  207,  and  also  the 
individual  compounds. 

4.  Just  as   the   alcohols   readily   give  up  water,  yielding 
olefines,  so  many  of  the  hydroxy  acids,  especially  the  ft-,  can 
be  transferred  into  unsaturated  monobasic  acids.     (See  Hydra 
cry  lie  Acid,  p.  216.) 

5.  When  warmed  with  hydriodic  acid,  the  hydroxy  acids 
are  reduced   to   the   corresponding  fatty  acids,    just  as  the 
alcohols  are  converted  by  this  reagent  into  hydrocarbons. 

6.  When  the  a-hydroxy  acids  are  warmed  with  dilute  sul- 
phuric acid,  formic  acid  is  produced  together  with  the  alde- 
hyde or  ketone  which  would  give  rise  to  the  acid,  according 
to  method  3.    The  /2-hydroxy  acids,  on  the  other  hand,  decom- 
pose into  water  and  acids  of  the  acrylic  series.     Thus : — 


CH3.CH:0-f  H- 
OH.CH2.CH2.CO2H  =  CH2:CH.CO2H  + 

The  a-,  /?-,  -y-,  &c.,  hydroxy  acids  also  differ  from  each 
other  in  the  facility  with  which  they  form  anhydrides.  (See 
Lactones,  p.  217.) 


GLYCOLLIC  ACID  209 

Glycollic  Acid,  Hydroxy-acetic  acid,  Ethanolic  add,  OH-CH2. 
C02H  (Strecker,  1848),  occurs  in  unripe  grapes,  in  the  leaves  of 
the  wild  vine,  &c. 

Formation. — 1.  By  the  oxidation  of  glycol  with  dilute  HN03 
( Wurtz). 

2.  Together  with  glyoxal  and  glyoxylic  acid,  by  the  oxida 
tion  of  alcohol  with  dilute  HN03. 

3.  By  the  reduction  of  oxalic  acid  with  Zn  +  H2S04. 

4.  From  formic  aldehyde  synthetically,  according  to  method 
3,  y.  206. 

5.  It  is  usually  prepared  by  boiling  chloro-acetic  acid  with 
water   in   the    presence   of   marble,    the    marble    serving  to 
neutralize  the  HC1  formed  in  the  reaction  (A.  200,  76): 

CH2C1.C02H  +  H20  ^±  OH.CH2.C02H  +  HC1. 

Properties. — It  forms  colourless  needles  or  plates,  is  readily 
soluble  in  water,  alcohol,  and  ether,  and  melts  at  80°.  Nitric 
acid  oxidizes  it  to  oxalic  acid.  The  alkaline  salts  are  hygro- 
scopic, the  calcium  salt  and  the  magnificent  blue  copper  salt 
are  sparingly  soluble  in  water.  K  =  0*0152. 

Derivatives. — (See  table,  p.  210.)  As  an  acid,  gly collie  acid 
forms  salts,  esters — e.g.  ethyl  glycollate — a  chloride,  glycollyl 
chloride,  and  glycollamide,  all  of  which  are  readily  hydro- 
lysed,  some  of  them  even  on  warming  with  water.  All  those 
derivatives  still  retain  their  alcoholic  character.  If,  on  the 
other  hand,  glycollic  acid  forms  derivatives  as  an  alcohol,  the 
properties  of  the  alcoholic  derivatives  in  question  are  combined 
with  those  of  an  acid,  since  the  hydroxyl  of  the  alcoholic 
group,  -CHg-OH,  enters  into  reaction,  while  the  carboxyl 
group  remains  unchanged.  These  derivatives  are  either 
ethers,  such  as  ethyl-glycollic  acid  (see  table),  or  e.g.  amines, 
such  as  glycocoll,  and,  as  alcoholic  derivatives,  they  are  not 
readily  hydrolysed;  or  they  are  esters  ^f  glycollic  acid,  as 
alcohol,  e.g.  acetyl-glycollic  acid,  CH2(0 .  CO  •  CH3) .  C02H,  or 
monocMoracetic  acid,  CH2C1-C02H  (the  hydrochloric  ester 
of  glycollic  acid),  and  then  they  are  of  course  saponifiable. 
These  latter  compounds  still  retain  their  acid  character,  and 
therefore  form,  on  their  part,  esters,  chlorides,  and  amides, 
which  are  also  readily  hydrolysed.  The  following  table  gives 
a  summary  of  the  more  important  derivatives  of  glycollic 
•acid : — 

(B480)  ° 


210 


IX.   HYDROXY  MONOBASIC  ACIDS 


Acid  Derivatives 

Alcoholic  Derivatives. 

Mixed  Derivatives. 

HO.CH2.CO-ONa 

Sodium  glycollate. 

NaO.CH2.CO-ONa 
Di-sodium  glycollate. 
Hygroscopic;   decomp. 
by  H^.0  into  Na  salt 
and  NaOH. 

HO.CH2.CO-OC2H5 
Ethyl  glycollate. 
Liquid,  b.-pt.  160°. 

OCiHs-CHa-CO-OH 

Ethyl-glycollio  acid. 
Liquid,  b.-pt.  206°. 

C2HS.O.CH2.CO.OC2H5 
Ethylic  ethyl-glycollate. 
Liquid,  b.-pt.  152°. 

HO-CH2.CO.C1 

Glycollyl  chloride. 
Oil  ;  decomposes  on 
volatilizing. 

CH2C1.CO.OH 
Moiiochloracetic 
acid. 

CH2C1-COC1 

Mon  ochloracety  1 
chloride.    Liquid,  b.-pt. 
120°,  of  suffocating 
odour. 

HO.CH2.CO.NHS 

Glycollamide. 
Crys.     M.-pt.  120°; 
does  not  form  salts 
with  bases. 

NH2.CH2.CO-OH 

Glycocoll. 
Crys.    M.-pt.  236°. 
Forms  salts  with 
acids  and  bases. 

NH2.CH2.CO.NH2 
Glycocollamide. 
Crys. 

It  is  easy  to  see  that  the  corresponding  derivatives  of  the 
first  and  second  vertical  rows  are  always  isomeric. 

Anhydrides  of  Glycollic  Acid. — 1.  Glycollic  acid  can  yield 
different  types  of  anhydrides:  (1)  the  elimination  of  one  mol. 
of  water  from  the  alcoholic  hydroxyls  of  two  molecules  of  the 
acid  produces  diglycollic  acid, 

2-CO2H 
2-C02H, 

which  is  obtained  by  boiling  monochloracetic  acid  with  lime. 
It  forms  large  rhombic  prisms,  is  a  dibasic  acid,  and,  as  an 
ether,  is  not  saponified  when  boiled  with  alkalis,  but  is  decom- 
posed when  heated  with  concentrated  hydrochloric  acid  to  120°. 
2.  Diglycollic  acid  loses  water  when  heated,  yielding  the 
diglycollic  anhydride, 


3.  Glycollic  anhydride,  OH.CH2.CO.O.CH2.CO2H,  is  an 
ester,  which  is  formed  when  glycollic  acid  is  heated  at  100°. 
It  becomes  hydrated  again  when  boiled  with  water,  and  may 
be  regarded  as  an  ester  derived  from  glycollic  acid  acting  as 
an  alcohol  and  as  an  acid. 


GLYCOCOLL  211 

CH2.O.CO 

4.  Glycohde,   -  .      ,  is  also  an  ester  anhydride,  and 

OU   •  U  •  Oiig 

is  isomeric  with  2  (and  with  fumaric  acid).  It  is  formed  when 
sodium  bromo-acetate  is  distilled  in  a  vacuum.  Lustrous 
plates;  m.-pt.  87°.  It  becomes  hydrated  again  when  boiled 
with  water. 

Glycocoll  (Ammo  -ethane  acid),  glycine,  amino-  acetic  add., 
NH2.CH2.C02H  (Braconnot,  1820).  This  is  the  simplest 
representative  of  the  important  class  of  amino  acids,  so  called 
because  they  are  derived  from  the  fatty  acids  by  the  exchange 
of  a  hydrogen  atom  of  the  hydrocarbon  radical  for  an  amino 
group,  e.g.  CH3.C02H,  acetic  acid;  CH2(NH2)  •  C02H,  amino- 
acetic  acid. 

Formation.  —  1.  By  the  action  of  concentrated  ammonia  upon 
monochloracetic  acid  (Heintz,  A.  122,  261;  Kraut,  A.  266,  292): 

CH2C1.C02H 


(cf.  also  B.  23,  Eef.  654).  Di-  and  triglycollamic  acids, 
NH(CH2.C02H)2  and  N(CH2  .  C02H)3,  are  produced  at  the 
same  time. 

a-Chloropropionic  acid  in  like  manner  yields  alanine  with 
ammonia  (see  Lactic  Acid).  The  method  is  a  general  one 
for  the  production  of  amino  acids. 

2.  By  boiling  glue  with  alkalis  or  acids. 

3.  Together  with  benzoic  acid,  by  decomposing  hippuric  acid, 
i.e.  benzoyl-glycocoll,  with  concentrated  hydrochloric  acid: 


Properties.  —  Glycocoll  forms  large  colourless  rhombic  prisms, 
readily  soluble  in  water,  but  insoluble  in  absolute  alcohol  and 
ether.  It  has  a  sweet  taste,  hence  the  name  "  glue  sugar  "  or 


glycocoll  (yXvKvs,  sweet,  KoAXa,  glue).  It  melts  and  decom- 
poses at  236°.  Glycocoll,  like  all  the  amino  acids,  possesses 
the  properties  of  both  an  amine  and  an  acid.  It  therefore 
forms  salts  with  acids  as  well  as  with  bases,  e.g.  glycocoll 
hydrochloride,  C2H5N02«HC1,  which  crystallizes  in  prisms,  and 
the  characteristic  copper  salt,  copper  glycocoll,  (C2H4N02)2Cu 
+  H2°>  which  crystallizes  in  blue  needles,  the  latter  being 
obtained  by  dissolving  cupric  oxide  in  a  solution  of  glycocoll. 
Most  of  the  other  amino  acids  also  form  characteristic  copper 
salts  of  this  nature,  which  serve  for  their  separation.  Glycocoll 


212  IX.   HYDROXY  MONOBASIC  ACIDS 

also  yields  compounds  with  salts,  and,  as  an  acid,  forms  an 
ethyl  ester,  an  amide,  &c.  (see  table,  p.  210).  When  heated 
with  BaO  it  is  decomposed  into  methyl-amine  and  C02,  while 
nitrous  acid  converts  it  into  glycollic  acid  (the  normal  reaction 
of  the  primary  amines).  With  ferric  chloride  it  produces  an 
intense  red,  and  with  copper  salts  a  deep-blue  coloration. 
Ethyl  armno-acetate  (b.-pt.  43°/ll  mm.)  and  nitrous  acid 

N\ 
yield  the  interesting  ethyl  diazo-acetate,  ||  yCH'CO'OC2H5, 

from  which  hydrazine,  NH2«NH2,  and  its  hydrate  were  first 
prepared;  and  from  the  latter  the  remarkable  compound, 
hydrazoic  acid,  N3H  (Curtius,  J.  pr.  Ch.  (2)  38,  396,  472;  43, 
207;  B.  24,  3341;  29,  759;  33,  58).  See  also  Di  and  Triazo 
Derivatives,  Chap.  LI. 

Constitution  (see  B.  16;  2650).  —  Free  glycocoll  may  possibly 
be   an  intramolecular  salt,  corresponding  with   the   formula 

CH2<Q^30>  (see  Taurine,  p.  197,  and  Betaine  below). 
Alkyl  and  Acyl  Derivatives  of  Glycocoll: 

Methyl-glycocoll      Trimethyl-glycocoll          Acetyl-glycocoll 
or  Sarcosine,  or  Betaine,  or  Aceturic  Acid, 

CH2.NHCH3  CH2.N(CH3 


00-  OH  CO-0  -  '  CO-OH. 

Most  of  these  alkyl  derivatives  are  interesting,  as  they 
either  occur  as  such  in  natural  products,  or  may  be  obtained 
by  the  decomposition  of  certain  natural  compounds.  Sar- 
cosine is  obtained  by  the  decomposition  of  the  complex 
natural  substances  creatine  or  caffeine.  Betaine  occurs  in 
beet-root,  and  is  present  in  large  quantities  in  the  molasses 
from  beet-root  sugar.  It  crystallizes  with  1  H20,  which  it  . 
readily  gives  up  on  heating.  This  hydrate  may  possibly  be 
C02H  •  CH2  •  NMe3  •  OH.  When  heated  at  293°  betaine  is 
transformed  into  the  isomeric  methyl  ester  of  dimethylamino- 
acetic  acid,  NMe2-CH2.CO«OMe;  at  higher  temperatures  it 
yields  trimethylamine.  It  has  been  synthesised  by  the  action 
of  trimethylamine  on  monochloracetic  acid  (B.  1902,  35,  603): 

d-CHj-COOH  ->  (CH3)3N(C1).CH2.CO.OH  —  (CH3)3N.CH2.CO. 

Numerous  other  compounds  of  a  similar  type  are  known,  and 
are  all  usually  termed  betaines. 


LACTIC  ACIDS 


213 


Lactic  Acids  (Hydroxy-propionic  acids).  (Wislicenus,  A.  128, 
1;  166,  3;  167,  302,  346.)— As  has  been  already  mentioned, 
two  isomeric  lactic  acids  are  theoretically  possible,  viz.  a-  and 
/3-hydroxy-propionic  acids,  a-  and  /?-lactic  acids,  or  ethylidene- 
and  ethylene-lactic  acids,  and  both  of  these  are  known. 

The  minute  investigation  of  the  different  lactic  acids  has 
been  of  very  great  importance  for  the  development  of  chemical 
theory;  they  were  formerly  held  to  be  dibasic,  and  the  recog- 
nition of  their  hydroxy-monobasic  nature  has  materially  con- 
tributed to  the  acceptation  of  the  theory  of  the  linking  of 
atoms. 

The  molecule  of  a-hydroxy-propionic  acid  contains  an 
asymmetric  carbon  atom, 


CHo-CH 


II 


and  hence  should  exhibit  exactly  the  same  kind  of  isomerism 
as  was  met  with  in  the  case  of  active  valeric  acid. 

In  reality  two  optically  active  a-lactic  acids  are  known,  one 
of  which  is  dextro  (d\  and  the  other  laevo  (I)  rotatory.  These 
two  acids  are  identical  in  all  their  properties,  with  the  excep- 
tion of  optical  activity.  A  mixture  (or  compound)  of  the 
two  in  equal  quantities  is  optically  inactive,  and  is  known  as 
inactive  (dl)  or  racemic  (r)  lactic  acid. 

The  molecule  of  /?-hydroxy-propionic  acid  does  not  contain 
an  asymmetric  carbon  atom,  and  hence  exists  in  only  one 
modification,  which  is  optically  inactive. 


i 
Modes  of  Formation. 

Fermentation  Lactic  Acid. 

Ethylene-lactic  Acid. 

i 
1.  By  the  regulated! 
oxidation  of       / 

a-Propylene  glycol, 
CH3.CH(OH).CH2OH. 

jS-Propylene  glycol, 
OH.CH2.CH2.CH2OH 

2.  By  the  exchange"! 
of   halogen   for  >- 

a-Chloro-propionic 
acid, 

S-Iodo-propionic  acid, 
CH2I.CH2.CO.OH. 

hydroxyl  in       J 

CH3.CHC1.CO-OH. 

3.  By  hydrolysis  of-! 

Aldehyde-cyanhydrin, 
CH3.CH(OH)-CN. 

E  t  hy  lene-cy  anhy  drin  , 
OH.CH2.CH2-CN. 

4.  B}f  action  of  ni-\ 

Alanine, 

irons  acid  upon/ 

CH3.CH(NH2).CO.OH. 

5.  By  the  reduction! 

Pyro-racemic  acid, 

of 

CHs-CO-CO-OH. 

6.  By  the  lactic  fermentation  of  sugar,  etc. 

214  IX.    HYDROXY  MONOBASIC  ACIDS 

1.  dl-Ethylidene- lactic  Acid  (Propane-2-ol-l-acid),  ordinary 
fermentation  lactic  acid,  CH3  •  CH  •  (OH)  •  C02H.  Discovered  by 
Scheele,  and  recognized  as  hydroxy-propionic  acid  by  Kolbe. 
Occurs  in  opium,  sauerkraut,  and  in  the  gastric  juice. 

Preparation. — This  depends  upon  the  so-called  lactic  fer- 
mentation of  sugars,  e.g.  milk,  cane-  and  grape-sugars,  and  of 
substances  related  to  them,  such  as  gum  and  starch;  it  is 
induced  by  certain  species  of  bacteria  commonly  spoken  of  as 
the  lactic  bacilli.  The  fermentation  proceeds  best  at  a  tempera- 
ture of  34°-35°  in  a  nearly  neutral  solution,  this  last  condition 
being  attained  by  the  addition  of  chalk  or  zinc-white  to  the 
fermenting  mixture.  The  free  acid  can  then  be  liberated 
from  the  lactate  of  zinc  by  sulphuretted  hydrogen.  When 
a  non-homogeneous  ferment  (e.g.  decaying  cheese)  is  used,  the 
lactic  acid  at  first  produced  is  readily  transformed  by  other 
organisms  into  butyric  acid  (p.  152). 

Lactic  acid  is  also  produced  in  large  quantity  by  heating 
grape-  or  cane-sugar  with  caustic-potash  solution  of  a  certain 
degree  of  concentration  (B.  15,  136).  The  relations  of  lactic 
acid  to  the  sugar  varieties  appear,  at  a  superficial  glance,  to 
be  very  simple;  thus  grape-sugar,  C6H1206,  and  lactic  acid, 
C3H603,  are  polymers. 

Lastly,  the  inactive  acid  is  produced  by  mixing  equal  quan- 
tities of  the  two  active  modifications.  In  syntheses  the  latter  are 
formed  in  equal  amounts,  and  hence  the  inactive  acid  is  obtained. 

Properties. — When  its  solution  is  evaporated  in  a  desiccator, 
a  thick,  non-crystallizing  and  hygroscopic  syrup  is  obtained, 
which  is  miscible  with  water,  alcohol,  and  ether,  and  which 
gradually  loses  water,  yielding  the  solid  lactic  anhydride, 
C6H1005,  before  all  the  water  of  solution  has  been  got  rid  of. 
To  obtain  the  pure  acid  it  is  necessary  to  distil  under  very 
low  pressures,  when  a  crystalline  solid  melting  at  18°  is 
obtained.  K  =  O0138.  When  heated,  it  is  partially  con- 
verted into  the  anhydride,  lactide,  C6H804,  and  partially  into 
aldehyde,  CO,  and  H20.  Similarly  it  decomposes  into  alde- 
hyde and  formic  acid  when  heated  with  dilute  sulphuric  acid 
to  130°,  concentrated  sulphuric  giving  rise  to  carbon  monoxide 
instead  of  formic  acid : 

CH3.CH(OH).CO2H  =  CH3.CHO  +  HCO2H. 

When  oxidized,  it  yields  acetic  and  carbonic  acids;  hydro- 
bromic  acid  converts  it  into  a-bromo-propionic  acid,  and  boiling 
hydriodic  acid  into  propionic  acid  itself. 


LACTIC  ACIDS  2l5 

The  inactive  acid  is  split  up  into  the  two  active  modifications 
by  the  crystallization  of  the  strychnine  salts  (Purdie  and 
Walker,  J.  C.  S.  1892,  754);  further,  when  green  mould,  Peni- 
cillium  glaucum,  is  sown  in  a  solution  of  the  ammonium  salt 
of  the  inactive  acid,  the  Isevo-acid  is  assimilated  more  rapidly 
than  the  dextro-,  and  the  solution  thus  becomes  optically 
active  (Linossier,  B.  1891,  24,  660).  A  very  simple  resolution 
has  been  accomplished  by  Purdie  (J.  C.  S.  1893,  1143)  by  crys- 
tallizing the  zinc  ammonium  salt,  ZnC6H1006,  NH4C3H503, 
2H20.  (Cf.  Eesolution  of  Racemic  Acid.) 

A  number  of  well-defined  salts  are  known,  e.g.  Calcium 
lactate,  (C3H503)2Ca  +  5H20;  zinc  lactate,  (C3H503)2Zn 
+  3H20;  ferrous  lactate,  (C3H503)2Fe  +  3H20.  When 
sodium  lactate  is  heated  with  sodium,  di- sodium  lactate, 
CH3  •  CH(ONa)  •  C02Na,  which  is  at  the  same  time  a  salt 
and  an  alcoholate,  is  formed. 

The  derivatives  of  lactic  acid  are  derivatives  of  it  either  as 
acid  or  as  alcohol,  and  are  perfectly  analogous  to  those  of 
glycollic  acid  (see  table,  p.  210).  Thus  ethyl-lactic  acid, 
a-ethoxy-propionic  acid,  CH3  •  CH(OC2H5)  •  C02H,  a  thick  acid 
liquid  which  boils  almost  without  decomposition,  corresponds 
with  ethyl-glycollic  acid;  ethyl  lactate,  which  can  be  distilled 
without  decomposition,  with  ethyl  glycollate;  lactamide, 
CH3.CH(OH).CO.NH9,  with  glycollamide;  and  alanine, 
CH3.CH(NH2).CO.OS,  with  glycocoll. 

By  the  action  of  PC15,  lactyl  chloride,  CHg-CHCl-CO-Cl 
(p.  171),  is  formed;  as  the  chloride  of  a-chloro-propionic  acid 
it  is  decomposed  by  water,  yielding  the  latter  acid  and  HC1. 

The  following  anhydrides  of  lactic  acid  are  known : — 

(1)  Lactylic  acid  or  Lactic  anhydride,  C6H1005,  which  is 
analogous  to  glycollic  anhydride,  and  forms  a  yellow  amor- 
phous mass.  (2)  Lactide,  C6H804,  analogous  to  glycolide 
(plates  melting  at  125°).  (3)  Dilactic  acid,  C6H1005,  the 
alcoholic  anhydride,  analogous  to  diglycollic  acid. 

2.  d-Ethylidene-lactic  acid,  Sarco-ladic  add,  para-lactic  acid 
(Liebig).  This  occurs  in  the  juice  of  flesh,  and  is  therefore  to 
be  found  in  Liebig's  extract  of  meat.  It  results  from  certain 
fermentations.  Its  chemical  properties  are  exactly  similar  to 
those  of  ordinary  lactic  acid;  thus  it  readily  yields  lactide  or 
aldehyde.  Its  salts  differ  to  some  extent,  however,  from  those 
of  the  latter;  thus,  the  zinc  salt,  +  2H20,  is  much  more  easily 
soluble,  and  the  calcium  salt  +  4H20,  much  more  sparingly 
soluble  than  the  corresponding  common  lactates.  Such  differ- 


216  ix.  HYDROXY  MONOBASIC  ACIDS 

ences  are  usually  met  with  between  d-  and  ^-compounds  on 
the  one  hand,  and  their  r-isomeride  on  the  other. 

3.  1-Ethylidene-lactic  acid  is  obtained  from  the  fermenta- 
tion of  cane-sugar  by  means  of  the  l-ladic  bacillus.     Its  salts 
correspond  exactly  with  the  salts  of  d-lactic  acid.     They  have 
the  same  formulae,  same  solubilities,  &c. 

4.  Ethylene-lactie  acid  (Propane-3-ol-l-acid),  hydracrylic  acid 
(Wislicmus,  A.  128,  1),  forms  a  syrupy  mass.     It  differs  from 
lactic  acid  (a)  by  its  behaviour  upon  oxidation,  yielding  car- 
bonic and  oxalic  acids,  and  not  acetic;  (b)  by  not  yielding  an 
anhydride  when  heated,  but  by  breaking  up  into  water  and 
acrylic  acid,  hence  the  name  hydracrylic  acid: 

CH2(OH).CH2.COOH  =  CH2:CH.COOH  +  H20; 

(c)  in  solubility,  and  in  the  amount  of  water  of  crystallization 
of  its  salts  (e.g.  zinc  salt,  +  4H20,  very  readily  soluble  in  water; 
calcium  salt,  +  2  H20).  It  is  not  so  strong  an  acid  as  a-lactic 
acid.  K  =  0-00311. 

It  may  be  synthesised  from  ethylene  by  means  of  the  fol- 
lowing series  of  reactions:  (a)  the  addition  of  hypochlorous 
acid,  (b)  conversion  of  the  chlorhydrin  into  the  corresponding 
nitrile,  and  (c)  hydrolysis,  e.g. : 

CH2:CH2  — *•  OH.CH2.CH2C1  -*  OH.CH2.CH2.CN 
-^  OH.CH2.CH2.C02H. 

Hydroxy-caproic  Acids,  Leucine  or  a-Amino-caproic  acid, 
CH3.CH2.CH2.CH2.CH(NH2).C02H,  is  a  derivative  of  a-hy- 
droxy-caproic.  It  forms  glistening  plates,  and,  like  other 
amino  acids,  is  closely  related  to  albumen.  It  is  found  in  old 
cheese,  also  abundantly  in  the  animal  organism  in  the  gastric 
gland,  and  in  the  shoots  of  the  vetch  and  gourd,  &c.  It  forms, 
along  with  tyrosine,  a  constant  product  of  the  digestion  of  al- 
bumen in  the  small  intestine  and  of  the  decay  of  albuminous 
substances,  and  is  formed  when  the  latter  are  boiled  with  alkalis 
or  acids.  It  has  also  been  prepared  synthetically.  It  closely 
resembles  glycocoll,  and  forms  a  characteristic  sparingly  soluble 
blue  copper  salt.  Leucine  is  dextro-rotatory.  A  laevo-  and  an 
inactive  modification  are  also  known  (B.  24,  669). 

LeSueur  (J.  C.  S.  1904,  827;  1905, 1888)  has  prepared  several 
hydroxy  derivatives  of  the  higher  fatty  acids,  e.g.  a-hydroxy- 
margaric  and  a-hydroxy-stearic  acids,  and  has  found  that  a 
good  yield  (35-60  per  cent)  of  an  aldehyde  can  be  obtained 
when  the  acid  is  heated  to  240-250°.  The  molecule  of  the 


LACTONES  217 

aldehyde  so  obtained  contains  a  carbon  atom  less  than  the 
molecule  of  the  hydroxy  acid,  and  water,  formic  acid,  carbon 
monoxide,  and  a  lactide  are  obtained  as  by-products. 

LACTONES 

All  hydroxy  acids  tend  to  lose  water  under  certain  con- 
ditions, yielding  anhydro-compounds. 

The  manner  in  which  this  water  is  eliminated  is  very 
different  in  the  various  types  of  hydroxy  acids. 

1.  In  the  case  of  the  a-hydroxy  acids,  1  or  2  mols.  of  water 
are  usually  eliminated  from  2  molecules  of  the  acid,  yielding 
compounds  of  the  type  of  diglycollic  acid,  glycollic  anhydride, 
&c. 

2.  In  /2-hydroxy  acids  1  molecule  of  water  is  usually  elimi- 
nated from  1  molecule  of  the  acid,  and  an  a-/3-unsaturated  acid 
is  formed,  e.g.  : 

CH3.CH(OH).CH2.C02H  ->  CH3.CH:CH.C02H  (crotonic  acid). 

3.  In  the  case  of  y-hydroxy  acids,  e.g.  y-hydroxy-butyric 
acid,  OH.CH2.CH2.CH2l.C02H,  1  molecule  of  water  is  elimi- 
nated from  1  molecule  of  the  acid,  and  an  inner  anhydride  or 
lactone  is  formed, 

2        2 


=  butyro-lactone  or  butanolid. 
CH2«CO  / 

The  formation  of  such  a  lactone  is  characteristic  of  y-hydroxy 
acids.  Many  of  these  acids  are  so  unstable  in  the  free  state, 
that  when  mineral  acid  is  added  to  their  salts  the  lactones  and 
not  the  free  acids  are  obtained. 

The  "y-lactones"  are  for  the  most  part  neutral  liquids  of 
faint  aromatic  odour,  readily  soluble  in  alcohol  and  ether,  and 
distilling  without  decomposition.  They  dissolve  in  alkalis, 
yielding  the  salts  of  the  corresponding  hydroxy  acids,  and  form 
brominated  fatty  acids  with  HBr,  and  amino  acids  or  amides 
of  y-hydroxy  acids  with  NH3  (B.  23,  Ref.  234). 

8-  and  /?-,  but  only  a  few  a-lac  tones,  from  8-,  /?-,  and  a-hy- 
droxy acids,  are  also  known.  They  show  marked  differences 
in  the  ease  with  which  they  are  formed  and  in  their  stability, 
the  y-lactones  being  the  most  stable.  (For  a-Lactones,  see  B. 
1891,  24,  4070;  for  ft-,  B.  1897,  30,  1954.) 

The  formation  of  lactones  by  warming  the  isomeric  unsatu- 
rated  acids,  CJI^f)^  which  contain  the  double  bond  in  the 


218  IX.    HYDHOXY  MONOBASIC  ACIDS 

/?-y  or  7-8  position,  with  HBr  or  with  moderately  concentrated 
H2S04,  is  worthy  of  note,  e.g. : 

E.CH:CH.CH2.CO2H  -*  K.CH.CH2.CH2.Cp. 


(For  details,  see  Fittig  and  his  pupils,  A.  208,  37,  111;  216, 
26;  255,  1,  275;  256,  50;  268,  110.) 

The  reaction  is  generally  regarded  as  the  addition  of  HBr 
or  H2O  to  the  double  bond,  and  then  the  elimination  of  the 
Br  or  OH  in  the  y-position  with  the  H  of  the  carboxyl  group. 

B.  Polyhydrie  Monobasic  Acids 

Just  as  glycol  on  oxidation  can  yield  the  monohydroxy 
monobasic  acid,  glycollic  acid,  so  the  polyhydric  alcohols  on 
careful  oxidation  with  nitric  acid  can  yield  polyhydroxy 
monobasic  acids,  e.g.: 

OH.CH2.CH(OH).CH2.OH  —  OH.CH2.CH(OH).C02H. 

They  are  usually  designated  according  to  the  number  of 
alcoholic  hydroxyl  groups  present.  This  number  can  be 
determined  by  converting  the  acid,  or  better,  its  ester,  into 
the  acetyl  derivative,  and  estimating  the  number  of  acetyl 
groups  by  analysis  or  by  hydrolysis  (p.  201). 

In  none  of  these  acids  do  we  find  more  than  one  OH  group 
attached  to  the  same  carbon  atom.  All  have  the  properties  of 
monobasic  acids  and,  in  addition,  the  properties  of  polyhydric 
alcohols.  Those  which  contain  a  hydroxyl  group  in  the 
y-position  yield  lactones. 

Most  of  the  compounds  belonging  to  this  class  either  crys- 
tallize badly  or  are  gum-like.  A  number  of  these  acids  are 
formed  by  the  cautious  oxidation  of  the  sugars  or  of  the 
unsaturated  acids,  CJi^.flz  (see  p.  162). 

I.  DIHYDROXY  MONOBASIC  ACIDS 

Glyceric  acid  (Propane-2:3-diol-l-acid),  OH.CH2-CH(OH). 
C02H,  is  a  syrupy  liquid  which  is  obtained  by  the  cautious 
oxidation  of  glycerol.  The  molecule  contains  an  asymmetric 
carbon  atom,  the  artificial  acid  is  optically  inactive,  but  a  d- 
and  an  /-modification  are  known  (Frankland,  J.  0.  S.  1891,  96). 

Various  compounds  obtained  from  natural  sources  are  closely 
related  to  the  dihydroxy  acids,  viz.  serine,  a-amino-^-hydroxy 


POLYHYDRIC  MONOBASIC  ACIDS  219 

propionic  acid,  obtained  by  boiling  silk  glue  with  dilute  acids; 
ornithine,  aS-diamino- valeric  acid;  and  lysine,  ae-diamino- 
caproic  acid,  obtained  by  the  hydrolysis  of  casein. 

II.  TETBA-  AND  PENTAHYDROXY  MONOBASIC  ACIDS 

The  tetra-  and  pentahydroxy  acids,  e.g.  OH  •  CH2  •  (CH  •  OH),  • 
C02H  and  OH.CH2.(CH.OH)4.C02H,  are  of  particular  im- 
portance, on  account  of  their  close  connection  with  the  simple 
sugars.  They  are  obtained  either  by  the  cautious  oxidation 
of  the  corresponding  sugars,  e.g.  by  means  of  bromine  water : 
or  by  the  reduction  of  the  corresponding  dibasic  acids  (sac- 
charic acid,  &c.);  or,  lastly,  by  the  addition  of  hydrocyanic 
acid  to  the  polyhydroxy  aldehydes  or  ketones,  just  as  lactic 
acid  is  formed  from  aldehyde.  Conversely,  the  acids,  in  the 
form  of  their  lactones,  are  on  the  one  hand  reconverted  into 
the  sugars  by  reduction  with  sodium  amalgam;  while,  on  the 
other  hand,  they  are  oxidized  by  nitric  acid  to  the  correspond- 
ing dibasic  acids. 

The  acids  are  named  according  to  the  sugar  to  which  they 
are  related:          Arabinose  ->  Arabonic  Acid, 
Glucose       — *•  Gluconic  Acid. 

(See  Sugars,  p.  300,  &c.) 

Some  of  the  acids  are  known  in  the  form  of  their  lactones 
only.  The  phenyl-hydrazones  are  frequently  made  use  of  for 
their  isolation. 

A  number  of  different  acids,  e.g.  mannonic,  gluconic,  gulonic, 
galactonic,  and  talonic  acid,  have  been  obtained  by  the  oxida- 
tion of  the  hexoses  (p.  307)  and  by  other  methods.  Inves- 
tigation has  shown  that  those  acids  all  possess  the  same 
structural  formula, 

OH  •  CH2 .  CH(OH)  •  CH(OH) .  CH(OH)  •  CH(OH)  •  CO2H, 

which  is  seen  to  contain  4  distinct  asymmetric  carbon  atoms. 

The  acids  are  thus  stereo-isomeric ;  their  differences  depend 
on  the  arrangement  in  space  of  the  different  radicals  (cf.  the 
Sugars). 

The  number  of  stereo-isomerides  possible  is  the  same  as  for 
the  sugars  (the  corresponding  aldo-hexoses),  viz.  eight  pairs 
of  optically  active  isomerides  and  eight  racemic  compounds. 
Most,  but  not  all,  of  these  have  been  obtained. 

Three  extremely  important  methods  have  been  employed 
(mainly  by  E.  Fischer)  for  the  preparation  of  these  acids:— 


220  IX.   HYDROXY  MONOBASIC  ACIDS 

1.  Oxidation  of  the  corresponding  aldehyde  (a  sugar),  e.g. 
ordinary  glucose  when  carefully  oxidized  with  chlorine-  or 
bromine-  water  yields  d-gluconic  acid: 

OH.CH2.(CH-OH)4.CH:O  ->  OH.CH2.(CH.OH)4.CO-OH. 

2.  From  a  stereo-isomeric  acid  by  intramolecular  transfor- 
mation under  the  influence  of  high  temperature,  and  generally 
in  the  presence  of  an  organic  base,  e.g.  d-gluconic  heated  with 
quinoline  and  water  yields  d-mannonic;  galactonic  —  *•  talonic. 

The  reaction  is  a  reversible  one,  and  hence  the  final  product 
is  a  mixture  of  the  two  acids,  which  can  be  separated  by  the 
difference  in  solubility  of  certain  of  their  salts. 

3.  The  addition  of  hydrogen  cyanide  to  a  polyhydric  alde- 
hyde or  ketone  and  subsequent  hydrolysis,  e.g.  : 


-OHVCHO  —  OH-CH2.(CH.OH)3.CH(OH).CN 
OH.CH2.(CH.OH)3.CH(OH).C02H. 

It  is  obvious  that  an  additional  asymmetric  carbon  atom  is 
introduced  by  the  addition  of  the  HCN,  and  thus  a  mixture 
of  two  stereo-isomeric  nitriles  is  formed,  and  on  hydrolysis  a 
mixture  of  two  stereo-isomeric  acids,  e.g.  : 

7  A  ,1  .         _  __  »-Z-Glucomc  acid 
-^-Mannonic  acid. 

This  reaction  is  somewhat  similar  to  the  addition  of  HCN 
to  acetaldehyde,  the  main  difference  is  that  the  original  com- 
pound is  optically  active,  and  hence  its  molecule  is  asymmetric. 
By  the  addition  of  HCN  two  compounds  are  obtained,  as  a 
rule  not  in  equal  amounts,  both  of  which  are  optically  active, 
but  do  not  stand  in  the  relationship  of  object  to  mirror  image. 

This  reaction  has  been  extended,  and  hydroxy  acids  con- 
taining 7,  8,  and  9  carbon  atoms  have  thus  been  obtained. 

C.  Hydroxy  Aldehydes 

As  examples,  we  have  glycollic  aldehyde,  OH  •  CH2  •  CH  :  0, 
aldol,  CH3.CH(OH).CH2-CH:0  (see  p.  131),  and  glyceric 
aldehyde,  OH.CH2.CH(OH).CH:O.  The  last-named  is  con- 
tained in  glycerose,  a  product  obtained  by  oxidizing  glycerol 
with  bromine  water.  Alkalis  convert  it  into  a  mixture  of 
sugars,  C6H1206  (see  a-Acrose).  (For  further  examples  of  hy- 
droxy aldehydes  and  ketones,  see  Sugars,  p.  300.) 


DIKETONES  221 

D.  Dialdehydes  (cf.  p.  97) 

Glyoxal  (Ethane-dial),  CHO-CHO  (Debus,  1856),  is  formed 
by  the  careful  oxidation  of  alcohol,  or  better,  of  aldehyde;  it 
possesses  all  the  characteristic  properties  of  aldehydes;  one 
molecule  of  the  aldehyde  is  capable  of  combining  with  two 
of  hydrogen  cyanide  or  of  sodium  hydrogen  sulphite. 

E.  Diketones 

1.  Diacetyl,  Butane-dione,  a-diketo-butane,  CH3«CO«GO«CH3, 
b.-pt.  87°-88°.     This  can  be  prepared  by  boiling  iso-nitroso- 
methyl  acetone,  CH3  -  C(  :  N  •  OH)  •  CO  •  CH3,  a  product  obtained 
by  the  action  of  nitrous  acid  on  methyl  ethyl  ketone,  with 
dilute  H2S04,  when  the  oximino  group  is  replaced  by  oxygen. 
It  is  a  yellow-green  liquid,  its  vapour  having  the  colour  of 
chlorine,  and  an  odour  similar  to  that  of  quinone  (v.  Pechmann, 
B.  20,  3162;  24,  3594;  Fittig  and  his  pupils,  A.  249,  182). 
Reduction  converts  it  into  dimethyl-ketol.     Homologues  are 
known  (cf.  B.  22,  2115). 

2.  Acetyl-acetone,  CH3.CO.CH2.CO-CH3,  is  formed  by 
the  action  of  aluminic  chloride  upon  acetyl  chloride  and  sub- 
sequent decomposition  of  the  aluminium  compound,  or  better 
(B.  22,   1009),  by  the  action  of  sodium  upon  a  mixture  of 
ethyl  acetate  and  acetone  (see  Aceto-acetic  ester  synthesis, 
p.  224): 

CH3.CO-OC2H6  +  CHo-CO 


It  is  a  liquid  which  boils  at  137°. 

3.  Acetonyl-  acetone,  y-diketo-hexane,  CH3»CO«CH2«CH2' 
CO-CH3,  may  be  prepared  from  monochlor-acetone  and  ethyl 
aceto-acetate  (B.  17,  2756);  also  from  diaceto-succinic  ester 
(B.  22,  168,  2100).  It  is  a  liquid  of  pleasant  odour,  and 
boils  at  188°. 

These  three  compounds  are  the  simplest  representatives  of 
the  a-,  ft-,  and  y-diketones,  or  of  the  1:2-,  1:3-,  and  l:4-di- 
ketones,  i.e.  of  those  diketones  whose  carbonyl  groups  are 
either  next  to  one  another  (a-position),  or  separated  by  ona 
carbon  atom  (^-position),  or  separated  by  two  (y-position). 

As  diketones  they  yield  mono-  and  dioximes,  and  also 
mono-  and  dihydrazones.  Such  dihydrazones,  and  also  those 


222  IX.   HYDROXY  MONOBASIC  ACIDS 

from   the   dialdehydes,    are    termed    osazones,    e.g.    diacetyl 
osazone. 

C6H6.NH.N:CMe.CMe:N.NH.C6H6. 

Osazones  are  also  formed  by  the  action  of  phenylhydrazino 
on  polyhydroxy  aldehydes  or  ketones,  e.g.  glucose  and  fructose, 
an  atom  of  oxygen  being  at  the  same  time  taken  up;  they  are 
mostly  yellow  in  colour  (cf.  the  phenyl-hydrazine  compounds 
of  the  carbohydrates). 

The  diketones  show  the  most  varied  behaviour  on  condensa- 
tion. By  the  action  of  alkali  on  the  a-diketones,  they  yield 
benzene  derivatives  (see  Quinone);  the  /3-diketones  readily 
pass  into  pyrazole  and  isoxy-azole  derivatives,  and  serve  for 
the  synthesis  of  derivatives  of  quinoline;  while  the  y-diketones 
are  easily  converted  into  derivatives  of  pyrrole,  furane,  and 
thiophene,  and  the  S-diketones  into  derivatives  of  pyridine  and 
tetrahydrobenzene. 

The  constitution  of  the  above  compounds  is  usually  deduced 
directly  from  their  mode  of  formation,  but  as  certain  of  them 
react  as  tautomeric  substances  (cf.  Ethyl  Aceto-acetate)  special 
physical  methods  have  also  been  used  (cf.  W.  H.  Perkin,  J.  C.  S. 
1892,  800). 

F.  Aldehydic  Monobasic  Acids 

Glyoxalic  acid  (Ethanal  add),  glyoxylic  acid,  CHO»C02H, 
occurs  in  unripe  fruits  such  as  grapes,  gooseberries,  &c.,  and 
may  be  prepared  by  superheating  dichloracetic  acid,  CHC12- 
C02H,  with  water,  2C1  being  here  exchanged  for  2  (OH),  and 
water  being  eliminated.  It  crystallizes  in  rhombic  prisms, 
dissolves  readily  in  water,  and  is  volatile  with  steam.  The 
acid  and  most  of  its  salts  contain  one  molecule  of  water  of 
crystallization,  which  points  to  the  formula  CH(OH)2  •  C02H, 
analogous  to  that  of  chloral  hydrate. 

Glycuronic  acid,  CHO  •  [CH(OH)]4  •  C02H.  The  lactone  of 
this  acid  forms  colourless  crystals,  which  melt  at  about  175°. 
The  acid  itself  is  obtained  from  saccharic  acid  by  reduction 
with  sodium  amalgam.  It  is  found  as  a  camphor  compound  in 
the  urine  of  dogs  after  camphor  is  administered  to  them. 

G.  Monobasic  Ketonie  Acids 

Ketonic  acids  are  compounds  which  contain  both  a  carbonyl 
and  a  carboxylic  group;  they  react  as  acids,  and  also  as  ketones; 


KETONIC  ACIDS  223 

thus,  besides  being  capable  of  forming  salts,  esters,  &c.,  they 
also  combine  with  sodium  bisulphite,  yield  oximes  with  hy- 
droxylamine  hydrochloride  (see  p.  135),  are  reduced  by  nascent 
hydrogen  to  hydroxy  acids,  and  so  on.  The  most  important 
members  of  this  class  are  pyroracemic  acid,  CH3»CO«C02H, 
aceto-acetic  acid,  CH3  •  CO  -  CH2  •  C02H,  and  Isevulic  acid, 
CH3.CO.CH2.CH2.C02H. 

Constitution  and  Nomenclature.  —  The  ketonic  acids  are  charac- 
terized theoretically  by  the  presence  of  carboxyl  and  of  car- 
bonyl,  the  latter  being  linked  to  carbon  on  both  sides.  They 
may  be  regarded  either  as  fatty  acids,  in  which  a  hydrogen 
atom  of  the  alkyl  group  has  been  replaced  by  acyl,  E»CO-,  as 
indicated  in  the  name  aceto-acetic  acid;  laevulic  acid  is  then 
/5-aceto-propionic  acid,  and  pyroracemic  acid  is  aceto-fonnic 
acid  ;  or  they  may  be  regarded  as  derived  from  the  fatty  acids 
by  the  replacement  of  the  two  hydrogen  atoms  of  a  CH2» 
group  by  an  atom  of  oxygen. 

In  the  latter  case  aceto-acetic  acid  is  to  be  designated 
j3-ketobutyric  acid,  or  butane-3-one-l-acid.  This  last  is  the  sys- 
tematic name  (Geneva  Congress);  the  expression  one  indicates 
the  presence  of  a  ketonic  group,  and  the  number  indicates  the 
relative  positions  of  the  ketonic  and  carboxylic  groups. 

The  constitution  of  a  ketonic  acid  is,  as  a  rule,  easy  to  deter- 
mine, either  from  its  synthesis  or  from  its  transformation  into 
the  corresponding  hydroxy  acids  of  known  constitution  by 
means  of  nascent  hydrogen. 

The  ketonic  acids  are  usually  divided  into  a,  /?,  and  y,  or 
1,  2,  and  3  ketonic  acids,  according  to  the  relative^positions  of 
the  carbonyl  and  carboxylic  groups.  CH3'CO'C02H,  pyro- 
racemic or  pyruvic  acid,  is  a  type  of  an  a-acid;  CH3'CO« 
CH2.C02H,  aceto-acetic  acid,  is  a  type  of  a  /3-acid;  and 
CH3.CO.CH2.CH2.C02H,  Isevulic  acid,  is  a  type  of  ay-acid. 
The  a-  and  y-acids  are  relatively  stable;  many  can  be  distilled 
without  undergoing  decomposition;  but  the  /3-acids  are  remark- 
ably unstable,  and  readily  lose  carbon  dioxide,  yielding  ketones. 
All  the  ketonic  acids  on  careful  reduction  yield  hydroxy  acids. 

Modes  of  Formation.—  I.  a-Ketonic  acids  are  formed  when 
the  acyl  cyanides  are  hydrolysed  (Claisen  and  SJiadwell)  (cf 
p.  179  and  B.  1898,  31,  1023): 


CH3.CO.CN  +  2H20  =  CH3.(X).C02H4-NH3 

Acetyl-cyanide  Pyroracemic  acid. 

The  constitution  follows  from  this  method  of  formation. 


224  IX.    HYDROXY  MONOBASIC  ACIDS 

2.  Aceto-acetic  and  other  /3-ketonic  acids  are  obtained  as 
esters  by  the  action  of  sodium  or  sodium  ethoxide  on  ethyl 
acetate  and  its  homologues: 

2(CH3.CO.OC2H5)  =  CH3.CO.CH2.CO.OC2H5  +  C2H6OH. 

According  to  Claisen  and  Lowman  (B.  20,  651;  26,  2130; 
38,  713),  the  ethyl  acetate  is  first  converted  by  the  sodium 
ethoxide  into  an  additive  compound: 

-C2H 


Na 

a  derivative  of  ortho-acetic  acid  (p.  142),  which  then  reacts 
with  another  molecule  of  ethyl  acetate,  thus:  — 


CH3 


=  CH3  .  C(ONa)  :  CH  .  CO2Et+2EtOH 


CH3.C(OH):CH.C02Et  —  CH3.CO.CH2.CO2Et. 

From  the  sodium  salt  thus  obtained,  the  aceto-acetic  ester 
can  be  liberated  by  acetic  acid,  probably  first  as  the  enolic  com- 
pound, which  is  immediately  transformed  into  the  ketonic. 

As  shown  in  the  above  formation  of  aceto-acetic  ester,  one 
molecule  of  ethyl  acetate  reacts  with  a  second  molecule.  Many 
reactions  of  an  analogous  nature,  in  which  the  two  reacting 
molecules  are  different,  may  be  brought  about  in  the  same 
way  by  the  aid  of  sodium  ethoxide  (W.  Wislicenus,  A.  246,  306). 
Thus  ethyl  oxalate  and  ethyl  acetate  react  in  the  presence  of 
sodium  ethoxide,  yielding  the  sodio  derivative  of  ethyl  oxal- 
acetate: 

(X)2Et.O);pEt+KCH2.CO2Et  =  C02Et.CO.CH2.CO2Et-f  EtOH. 

Esters  also  readily  react  with  ketones,  with  the  formation  of 
diketones  (L.  Claisen): 

CH3.CO-OEt  +  CH3.CO.CH3  =  CH3.CO-CH2.CO.CH3  +  EtOH 

Acetyl-acetone. 

When  ethyl  formate  is  employed,  ketonic  aldehydes  are  not 
obtained,  but  their  structural  isomers,  hydroxy-methylene 
compounds;  with  acetone,  for  example,  hydroxy-methylene- 
acetone,  thus:  — 

H  •  CO  •  OC2H5+CH3  •  CO  •  CH3  =  CH(OH)  :  CH  •  CO  -  CH3+C2H5  •  OH 

Ethyl  formate  Hydroxy-methylerie-acetone. 


a-KETONIC  ACIDS  225 

This  condensation  between  esters,  or  between  esters  and 
ketones,  in  the  presence  of  sodic  ethoxide  is  usually  known  as 
Claisen's  reaction,  and  is  of  extreme  importance  as  a  synthe- 
tical process.  (For  summary  see  B.  1905,  38,  709.) 

In  all  cases,  according  to  Claisen,  the  condensation  is  pre- 
ceded by  the  formation  of  an  additive  compound  between  the 
sodium  ethoxide  and  the  ester.  As  a  rule,  metallic  sodium 
and  not  sodium  ethoxide  is  added  to  the  ester  (e.g.  to  ethyl 
acetate  in  the  preparation  of  ethyl  aceto-acetate),  but  the 
reaction  only  proceeds  when  the  ester  contains  free  alcohol, 
and  can  thus  give  rise  to  sodic  ethoxide.  Quite  recently  (Ber. 
1905,  38,  693)  the  same  chemist  has  shown  that  sodamide, 
Na«NH2,  may  be  used  in  place  of  sodic  ethoxide. 

Michael  (B.  1900,  33,  3731,  and  1905,  38,  1922)  considers 
that  the  Claisen  condensation  proceeds  in  a  different  manner, 
and  that  it  may  be  compared  with  the  aldol  condensation. 
Compare  also  Stoermer  and  Kippe  (B.  1905,  38,  1953). 

3.  Higher  homologues  of  aceto-acetic  ester  (/3-ketonic  acids) 
are  easily  obtained  from  it  by  the  action  of  sodium  ethoxide 
and  alkyl  halides  (p.  228). 

4.  Ketonic  acids  are  produced  by  the  cautious  oxidation  of 
hydroxy  acids  containing  the  secondary  alcoholic  group: 


CH3.CH(OH).CO.OH  +  0  =  CH^CO-CO-OH  + 

Lactic  acid  Pyroracemic  acid. 

a-Ketonic  Acids,  —  Pyruvic  or  pyroracemic  acid,  GEL-  CO* 
C02H,  is  a  liquid  which  is  readily  soluble  in  water,  alcohol, 
and  ether,  boils  with  slight  decomposition  at  165°-170°,  and 
smells  of  acetic  acid  and  extract  of  beef.  It  is  formed  by  the 
dry  distillation  either  of  tartaric  or  of  racemic  acid,  hence  its 
name. 

In   this    decomposition    carbon    dioxide   is    probably   first 
evolved  and  gly  eerie  acid  formed: 
CO?:H.CH(OH).CH(OH).C02H  ->  CH2(OH).CH(OH).GX32H. 

This  then  loses  water,  yielding  pyruvic  acid. 

It  may  also  be  obtained  by  methods  1  and  4. 

Pyroracemic  acid  has  a  tendency  to  polymerize.  Nascent 
hydrogen  reduces  it  to  ethylidene-lactic  acid: 

CH3.CO.C02H  +  2H  =  CH3.CH(OH).C02H. 
It  is  a  relatively  strong  acid  owing  to  the  negative  nature 

(B480)  ? 


226  IX.   HYDROXY  MONOBASIC  ACIDS 

of  the  CO  group,  K  =  0*56.  It  reacts  as  a  ketone  with 
phenyl-hydrazine,  hydroxylamine,  and  hydrogen  cyanide. 

The  phenyl-hydrazone  crystallizes  readily,  melts  at  192° 
when  quickly  heated,  and  is  largely  made  use  of  in  detecting 
the  acid.  The  acid  also  resembles  the  ketones  in  the  readiness 
with  which  it  forms  condensation  products,  yielding  either 
benzene  derivatives  (B.  5,  956),  or — in  presence  of  ammonia — 
those  of  pyridine. 

The  electrolysis  of  a  concentrated  solution  of  the  potassium 
salt  proceeds  in  the  normal  manner,  the  CH3  •  CO  •  COO  • 
groups  formed  at  the  anode  yield  diacetyl  and  carbon  dioxide 
(cf.  Electrolysis  of  potassium-acetate  solution),  but  secondary 
reactions  also  occur,  and  acetic  acid  is  formed  to  a  certain 
extent. 

/2-Ketonic  Acids.— Aceto-aeetic  acid,  CH3.CO.CH2-C02II, 
is  a  strongly  acid  liquid,  miscible  with  water,  and  breaking  up 
into  acetone  and  carbonic  acid  when  warmed.  It  is  prepared 
by  the  cautious  hydrolysis  of  its  ethyl  ester  (B.  15,  1376, 1871). 
Its  aqueous  solution  is  coloured  violet-red  by  ferric  chloride. 
The  Na-  or  Ca-salt  is  sometimes  contained  in  urine  (B.  16, 
2314).  Its  constitution  as  acetone-carboxylic  acid  follows  from 
the  products  of  decomposition. 

The  ethyl  ester,  ethyl  aceto-acetate,  or  commonly  called 
aceto -acetic  ether,  is  prepared  by  the  Claisen  condensation 
method  (general  method  2).  It  is  liberated  from  the  sodium 
derivative  by  the  addition  of  acetic  acid,  and  purified  by 
distillation  under  reduced  pressure.  It  boils  at  181°,  or  at 
71°  under  12'5  mm.  pressure,  is  only  slightly  soluble  in  water, 
but  readily  in  alcohol  and  ether,  and  has  a  pleasant  fruity 
odour.  Ferric  chloride  colours  its  aqueous  solution  violet-red. 
Extremely  characteristic  are  the  products  to  which  it  can  give 
rise  on  hydrolysis. 

1.  Normal  Hydrolysis. — As  an  ester,  it  can  be  hydrolysed 
to  the  corresponding  acid  and  alcohol,  viz.  aceto -acetic  acid 
and  ethyl  alcohol.     This  reaction  occurs  only  when  the  ester 
is  extremely  carefully   hydrolysed   in   the  cold   with  dilute 
alkali. 

2.  Ketonic  Hydrolysis. — This  hydrolysis  is  best  accomplished 
by  the  aid  of  dilute  sulphuric  acid  or  baryta  water, 

CH3.CO.CH2.:COOiC2H6 
H;         iOH, 

the  products  being  acetone,  carbon  dioxide,  and  ethyl  alcohol 


ETHYL  ACETO-ACETATE  227 

3.  Add  Hydrolysis.  —  This  takes  place  most  readily  when  the 
ester  is  heated  with  concentrated  alcoholic  potash  or  soda, 

CH3.CO:  .CH2.COO:C2H5 

HO;H        Hiofe, 

the  products  being  acetic  acid  and  ethyl  alcohol. 

Ethyl  aceto-acetate  has  been  represented  by  the  formula 
CH3  •  CO  •  CH2  •  C02Et,  and  undoubtedly  numerous  arguments 
can  be  brought  forward  in  favour  of  this  constitution;  e.g.  it 
reacts  with  sodic-hydric  sulphite,  with  hydrogen  cyanide,  and 
with  hydroxylamine  as  a  ketone,  and  hence  should  contain 
the  C-CO'C  group;  a  further  argument  for  the  ketonic  con- 
stitution is  to  be  found  in  the  decomposition  of  the  acid  into 
acetone  and  carbon  dioxide  ;  on  the  other  hand,  with  ammonia 
or  amines  it  gives  /5-amino,  or  substituted  /3-amino  crotonic 
acids,  e.g.  CH3  •  CH(NH2)  :  CH  •  C02H,  and  with  phosphorus 
pentachloride  it  yields  /5-chloro-crotonic  acid,  CH3-CC1:CH- 
C02H.  These  latter  reactions  could  be  most  readily  explained 
by  assuming  the  constitution  CH3  •  C(OH)  :  CH  •  C02Et,  i.e.  ethyl 
/3-hydroxy-crotonate  for  ethyl  aceto-acetate.  The  ester  is  thus 
a  typical  tautomeric  substance,  reacting  as  though  it  possessed 
two  distinct  constitutions,  and  a  study  of  the  chemical  proper- 
ties alone  will  not,  as  a  rule,  permit  us  to  settle  with  certainty 
which  of  the  two  is  the  more  probably  correct. 

The  following  suggestions  have  been  made  to  account  for 
the  tautomerism:  — 

(a)  The  ester  is  really  a  mixture  of  the  two  distinct  com- 
pounds. 

(b)  The  pure  ester  is  unstable,  and  although  it  may  have 
the  one  constitution,  e.g.  ethyl  aceto-acetate  or  ketonic  con- 
stitution, in  the  presence  of   various  reagents  it  is  readily 
transformed  into  the  isomeric  compound  with  the  enolic  con- 
stitution, i.e.  ethyl  /3-hydroxy  crotonate.     This  type  of  tauto- 
merism is  thus  often  spoken  of  as  keto-enolic  tautomerism^ 
and  is  frequently  met  with  (see  Phloroglucinol,  &c.).     Accord- 
ing to  this  view,  it  consists  in  the  wandering  of  a  hydrogen 
atom  and  a  change  in  position  of  a  double  bond  (desmotropism). 


(c)  According  to  Van  Laar,  the  tautomerism  is  due  to  an 
oscillatory  hydrogen  atom,  which  cannot  be  regarded  as  per- 


228  IX.   HYDROXY  MONOBASIC  ACIDS 

manently  attached  to  C  or  to  0,  but  as  continually  oscillating 
between  the  two. 

Physical  methods  have  been  used  for  elucidating  the  consti- 
tution of  such  compounds.  The  most  important  of  these  are 
the  molecular  refraction  (Gladstone,  Bruhl),  the  molecular  mag- 
netic rotation  (W.  H.  Perkin,  Sen.,  J.  C.  S.  1892,  800),  and 
the  absorption  of  electric  waves  (Drude,  B.  1897,  30,  940). 
[Compare  chapter  on  Relationship  between  Physical  Properties 
and  Chemical  Constitution.]  The  conclusions  arrived  at  from 
such  a  study  are  (a)  that  ethyl  aceto-acetate  is  a  mixture  in 
chemical  equilibrium  of  the  ketonic  and  enolic  forms,  but  con- 
sists mainly  of  the  ketonic  compound,  and  (b)  that  a  rise  of 
temperature  favours  the  ketonic  form.  (See  also  Baly  and 
Desch,  J.  C.  S.  1904,  1029;  1905,  766.) 

The  metallic  derivatives  are  enolic  compounds. 

1.  Ethyl  Aceto-acetate  as  a  Synthetical  Reagent.— One 
atom  of  hydrogen  in  the  aceto-acetic  ester  molecule  is  readily 
replaceable  by  metals  (Geuther;  Conrad,  A.  188,  269).  The  sodio 
derivative  is  formed  together  with  hydrogen  on  the  addition 
of  sodium,  and  also  when  an  alcoholic  solution  of  the  ester 
is  mixed  with  the  calculated  amount  of  sodium  ethoxide  in 
absolute  alcohol: 

CH3.CO.CHNa.CO2Et    or    CH3.C(ONa):CH.CO2Et. 

This  sodio  derivative  forms  long  needles  or  a  faintly  lustrous 
loose  white  mass.  The  copper  salt  crystallizes  in  bright-green 
needles. 

The  sodium  is  readily  replaced  by  alkyl  radicals  when  the 
sodio  derivative  is  heated  with  an  alkyl  bromide  or  iodide; 
sodium  bromide  or  iodide  is  thus  formed  together  with  alky- 
lated  aceto-acetic  esters,  which  are  of  great  interest  in  various 
syntheses,  e.g.:  ethyl  methylacetoacetate,  CH3-CO.CH(CH)3. 
C02C2H5,  and  the  corresponding  ethyl-  and  propyl-acetoacetic 
esters,  &c.  In  these  compounds  the  hydrogen  atom  of  the  CH 

rup  may  be  again  replaced  by  Na,  and  this  again  substituted 
alkyl,  with  the  production  of  dialkylated  aceto-acetic  esters, 
e.g.:  dimethylacetoacetic  ester  or  ethyl  dimethylacetoacetate, 
CH3.CO.C(CH3)2.C02C2H5;   methylethylacetoacetic  ester, 
CH3.CO.C(CH3)(C2H5).C02C2H5,  and  so  on. 

These  alkylated  aceto-acetic  esters  exactly  resemble  the 
mother  substance,  especially  in  the  manner  in  which  they 
can  be  decomposed  by  either  the  "ketonic  hydrolysis"  or 
the  "acid  hydrolysis"  (cf.  p.  226).  The  formation  of  ketone 


ACYL  DERIVATIVES  OF  ETHYL  ACETO ACETATE    2^9 

largely  predominates  when  dilute  acid  is  employed,  and  of 
fatty  acids  when  concentrated  alkali  is  used. 

In  the  ketonic  hydrolysis  the  alkyl  groups  introduced  are 
left  attached  to  a  carbon  atom  of  the  acetone  molecule,  e.g. : 

_  =  EtOH  +  C02  +  CH3.CO.CHMeEt. 

This  affords  a  very  general  method  for  the  synthesis  of  some 
of  the  higher  ketones. 

In  the  acid  hydrolysis  the  alkyl  groups  remain  attached  to 
a  carbon  atom,  which  is  united  to  a  carboxylic  group,  e.g. : 

EtOH. 


This  affords  a  simple  method  for  synthesising  any  mono-  or 
dialkylated  acetic  acid,  e.g.:  CH3 •  CH2 •  C00H ;  C2H5-CH2. 
C02H;  (CH3)(C2H5)CH.C02H;  (CH3)(C3Hr)CH . C02H.  (Cf. 
Ethyl  malonate  synthesis,  p.  237;  also  Wislicenus  and  his 
pupils,  A.  186,  161.) 

2.  Acyl  groups  may  be  introduced  in  place  of  alkyl  radi- 
cals into  aceto-acetic  ester  by  similar  methods,  e.g.  from  acetyl 
chloride,  diaceto- acetic  ester,  (CH3 .  CO)2CH .  C02C2H5.    The 
product  obtained  varies  with  the  conditions.     When  an  acyl 
chloride  reacts  with  the  sodio-derivative  of  ethyl  acetoacetate 
the  chief  product  is  the   C-acyl  derivative,  viz.  (CH3»CO) 
(R.CO)CH-C02Et,  but  when  the  free  ester  is  treated  with 
an  acyl  chloride  in  the  presence  of  pyridine  the  isomeric  0-acyl 
derivative  is  obtained,  e.g.  R .  CO  •  0 .  C .  CMe :  CH  -  C02Et.    The 
0-derivatives,  when  heated  or  when  warmed  with  potassium 
carbonate,  are  transformed  into  the  isomeric  C-compounds. 

Ethyl  chlorocarbonate  and  the  sodio-derivative  yield  the 
0-derivative  CH3 .  C(0  •  C92Et) :  CH  -  C02Et  together  with  a 
small  amount  of  the  C-derivative,  aceto-malonic  ester,  (CH3* 
CO)  •  CH(C09CJEL)9;  from  monochloracetic  ester,  CH2C1  • 
C02C2H5,  aceto-succinic  ester,  CH3.CO.CH(CH2.C02C2H5) 
(C02C2H5)  may  be  similarly  obtained  (see  Malonic  and  Suc- 
cinic  acids,  and  also  the  Synthesis  of  dibasic  acids),  &c. 

3.  Iodine  acts  upon  sodio-aceto-acetic  ester,  yielding  diaceto- 
succinic  ester: 

CH3.CO.CHNa.C02C2H5  CH3.O).CH.C02C2H6 

+  l2  ""  GH.-CO.CH.CO.C.H. 


230  IX.    HYDKOXY   MONOBASIC  ACIDS 

4.  In  addition  to  the  above-mentioned  simple  syntheses,  d 
number  of  more  complex  syntheses  may  be  effected  by  means 
of  ethyl  acetoacetate.  Many  of  these  lead  to  the  formation  of 
closed-chain  compounds,  and  will  be  described  in  connection 
with  the  various  groups  of  ring  compounds.  The  following 
may  be  mentioned  as  the  more  important: — 

(a)  Hantzsch's  synthesis  of  pyridine  derivatives,  e.g.  ethyl 
dihydrocollidine  dicarboxylate, 

<Me:C(C02Et)>CHMe) 


!:C(C02Et) 

by  heating  ethyl  acetoacetate  with  aldehyde  ammonia. 

(b)  The  formation  of  oxyuvitic  acid  (a  benzene  derivative), 
C6H2(CH3)(OH)(C02H)2,  by  the  action  of  chloroform  on  the 
sodio-derivative. 

(c)  The  formation  of  methyluracyl  by  the  condensation  of 
ethyl  acetoacetate  with  urea, 

*       nn^NH2  i  Et°  •  OOxnTT  nn/NH  •  CO v  nTT 

^•vXTTT     T  OTT      CV^s^^      2     ™     "     ^-^\"\TTT    rVr~<TT\  *&***•"•• 
^1»  X±2          vXlg  •  \j\J'  ^1>  ±1  •  \j\\jl±)^ 

(See  p.  287  and  Synthesis  of  Uric  Acid,  p.  291.) 

(d)  The  production  of  furane  and  pyrrole  derivatives  by 
heating  ethyl  diacetosuccinate  (see  Synthesis  3)  with  acids 
or  with  ammonia  and  amines. 

(e)  The  synthesis  of 


Phenylmethylpyrazolone  Phenyldimethylpyrazolone 

by  the  condensation  of  ethyl  acetoacetate  with  phenylhydra- 
zine  and  methylphenylhydrazine  respectively. 

Chlor-  and  dichlor-aceto-acetic  esters,  which  are  very  active 
chemically,  are  produced  by  the  replacement  of  the  H  of  the 
methylene  group  by  Cl.  The  two  methylene  hydrogen  atoms 
are  also  replaceable  by  the  isonitroso  group,  :N'OH  (by  the 
action  of  NoOA  and  by  the  imido  group,  :NH  (cf.  A.  226. 
294;  B.  28,  2683). 

Laevulic  acid,  CH3 .  CO  •  CH2 .  CH2  •  C02H,  forms  crystalline 
plates,  melts  at  33°,  and  boils  at  239°.  It  is  formed  by  the 
action  of  acids  upon  cane-sugar,  laevulose,  cellulose,  gum, 
starch,  and  other  carbohydrates  (A.  175,  181;  206,  207),  and 
has  also  been  prepared  synthetically.  (For  its  constitution, 
cf.  A.  256,  314.)  It  is  employed  in  cotton  printing  and  for 
the  preparation  of  anti-thermine,  &c. 


DIBASIC  ACIDS 


231 


X.  DIBASIC  ACIDS 

Dibasic  acids  are  those  which  are  capable  of  forming  two 
series  of  salts,  viz.  acid  and  normal,  and  likewise  two  series  of 
esters,  chlorides,  amides,  &c.  They  are  characterized  by  the 
presence  of  two  carboxyl  groups  in  the  molecule. 

A.  Saturated  Dibasic  Acids,  CUH2U_204>  OP  Acids 
of  the  Oxalic  Series 


Name. 

Formula. 

Melting-pt. 

K. 

Oxalic  

CO2H- 

C02H- 
CO9H- 
COgH- 
CO,H. 

CO^H. 

C02H. 

C02H 

CH9. 
[CHlo] 

cnr 
'CH;S 

'CH2 

;cH2. 

C02H 
2-CO2H 
3.C02H 
4-CO2H 
5-CO2H 
6-C02H 

)'  Sublimes  1 
\  150°-160°  J 
132° 
185° 
97'5° 
149° 
105° 
140° 

10-0 

0-016 
0-0065 
0-0047 
0-00371 
0-00323 
0-00258 

Malonic  

Succinic  

Grluteivic 

Adipic  
Pimelic 

Suberic  .       . 

The  above  are  solid  crystalline  compounds  of  strongly  acid 
character,  and  most  of  them  are  readily  soluble  in  water. 
When  heated,  they  either  yield  an  anhydride,  or  carbon  di- 
oxide is  eliminated  and  a  monobasic  acid  formed;  but  most  of 
them  can  be  volatilized  in  vacuo. 

Formation. — 1.  By  the  oxidation  of  the  di-primary  glycols. 
(See  table,  p.  204.) 

la.  By  the  oxidation  of  hydroxy-acids  and,  generally,  of 
many  complex  compounds,  such  as  fats,  fatty  acids,  and  carbo- 
hydrates. 

2.  By  the  hydrolysis  of  the  corresponding  nitriles;  thus, 
oxalic  acid  is  formed  from  cyanogen,  and  succinic  acid  from 
ethylene  cyanide: 

(CN)2  +  4H20  =  (C02H)2  +  2NH3. 
)2.CN  +  4H20  =  C02H.(CH2)2-C02H. 


CN.(CH2)2. 

Since  ethylene  cyanide  is  a  glycol  derivative,  its  conversion 
into  succinic  acid  represents  the  synthesis  from  a  glycol  of  an 
acid  containing  two  atoms  of  carbon  more  than  itself,  i.e.  the 
oxcnange  of  2  (OH)  *or  2'/XX,H),  or  the  indirect  combination 
of  ethylene  with  2(CO?H/. 


232  x.  bl&Aslo 

3.  By  the  hydrolysis  of  the  cyano-fatty  acids  (p.  170),  and 
consequently  from  the  halogen  fatty  acids  also.     Thus  chloro- 
or  cyaho-acetic  yields  malonic  acid,  /3-iodo-  (or  cyano-)  propionic 
acid,  common  succinic  acid,  and  a-iodo-  (or  cyano-)  propionic 
acid,  methyl  malonic  acid. 

A  dibasic  acid  can  therefore  be  formed  from  each  hydroxy- 
acid  by  the  exchange  of  OH  for  C02H,  or  indirectly  from  a 
fatty  acid  by  the  replacement  of  H  by  C02H.  Thus : — 

02H--  CH2(CN).C02H-> CH2(C02H)2. 

4.  The  homologues  of  malonic  acid  can  be  prepared  from 
malonic  acid  itself  by  a  reaction  exactly  analogous  to  the  aceto- 
acetic  ester  synthesis  (the  "Malonic  ester  synthesis",  p.  238). 

The  dibasic  acids  are  also  obtained  by  means  of  the  aceto- 
acetic  ester  synthesis.  Aceto-malonic  and  aceto-succinic  acids, 
which  have  already  been  mentioned  at  p.  229,  yield  respec- 
tively malonic  and  succinic  acids  by  the  elimination  of  acetyl 
("  acid  decomposition  "). 

5.  Higher  homologues  are  obtainable  by  the  electrolysis  of 
the  ethyl  potassium  salts  (p.  234)  of  the  simpler  dibasic  acids, 
e.g.  adipic  acid  from  potassium  ethyl  succinate. 

The  reaction  is  exactly  analogous  to  the  formation  of  ethane 
by  the  electrolysis  of  potassium  acetate.  For  example,  with 

potassium  ethyl  succinate  the  anions  C02Et  •  CH,  •  CH2  •  C0,2  • 

+ 

and  kations  K  are  present.  When  these  become  discharged  at 
the  electrodes  during  electrolysis,  each  C02Et  •  CH2  •  CH2  •  C02 
group  splits  up  into  carbon  dioxide  and  the  monovalent  radical 
CO2Et  •  CH2  •  CH2  • .  Two  such  radicals  then  combine,  yielding 
ethyl  adipate,  C02Et  •  CH2  •  CH2  •  CH2  •  CH2  •  C02Et.  The  potas- 
sium formed  at  the  cathode  reacts  with  the  water,  yielding 
hydrogen  and  potassium  hydroxide. 

The  constitution  of  the  acids  CnH2n_204  is,  as  a  rule,  very 
easy  to  determine  from  the  above-mentioned  modes  of  for- 
mation, especially  2,  3,  and  4.  According  to  these,  one  has 
to  decide  between  the  malonic  acids  proper,  i.e.  malonic  acid 
and  its  alkyl  derivatives  (p.  238),  whose  two  carboxyl  groups 
are  both  linked  to  one  carbon  atom: 

CH2(CO2H)2,        E  -  CH(CO2H)2,        EE'C(CO2H)2, 

and  ordinary  succinic  acid  and  its  homologues,  which  contain 
the  carboxyls  bound  to  two  different  carbon  atoms. 


PROPERTIES  OF  DIBASIC  ACIDS  233 

The  bivalent  acid  residues,  C202  =  oxalyl,  C3H202  =  malonyl, 
and  C4H402  =  succinyl,  which  are  combined  with  the  two  hy- 
droxyls,  are  termed  the  radicals  of  the  dibasic  acids,  and  are 
examples  of  bivalent  acyl  radicals. 

homers. — Isomers  of  oxalic  and  malbnic  acids  ate  neither 
theoretically  possible  nor  actually  known.  We  know,  how- 
ever, two  succinic  acids,  viz. : 

CX)2H.CH2.CH2.C!O2H    and    CH3.CH(CO2H)2. 

The  former  corresponds  with  ethylene  chloride  and  the  latter 
with  ethylidene  chloride,  from  which  they  are  respectively 
derived  by  the  exchange  of  two  chlorine  atoms  for  two  car- 
boxyls.  Hence  the  names  ethylene-  and  ethylidene-succinic 
acids,  or  more  commonly  succinic  acid  and  methylmalonic  acid. 

Since  ethylene  cyanide  can  be  prepared  from  the  chloride, 
the  above  derivation  of  ethylene-succinic  acid  is  also  an  experi- 
mental one.  This  is  not  the  case,  however,  with  the  isomeric 
acid,  since,  as  a  rule,  when  several  chlorine  atoms  are  bound 
to  the  same  carbon  atom,  as  in  ethylidene  chloride,  they  cannot 
be  exchanged  for  cyanogen. 

Behaviour. — Many  of  the  dibasic  acids,  in  the  molecules  of 
which  the  carboxyls  are  attached  to  different  carbon  atoms, 
yield  intramolecular  anhydrides  by  the  elimination  of  a  mole- 
cule of  water  from  one  of  the  acid.  These  anhydrides  may 
be  obtained  either  (1)  by  heating  the  acids  alone,  or  (2)  more 
generally  by  the  action  of  phosphorus  pentachloride,  acetyl 
chloride,  or  carbonyl  chloride  upon  the  acids  (B.  10,  1881;  17, 
1285).  They  recombine  slowly  with  water  to  form  the  free 
acids.  This  formation  of  anhydride  is  favoured  by  the  presence 
of  substituents  in  the  molecule  (B.  23,  101,  620;  26,  1925). 

The  elimination  of  water  occurs  most  readily  with  succinic 
and  glutaric  acids  and  their  substituted  derivatives;  in  fact, 
with  the  acids  containing  a  chain  of  4  or  5  carbon  atoms : 

C02H.C.C.C02H    and    C02H.C.C.C. 

This  is  undoubtedly  to  be  attributed  to  the  spatial  relation- 
ships of  the  atoms  within  the  molecule.  Assuming  that  the 
four  valencies  of  a  carbon  atom  are  symmetrically  distributed 
in  space  (i.e.  directed  towards  the  solid  angles  of  a  tetra- 
hedron), then  it  can  be  readily  seen  by  the  aid  of  models  that 
in  acids  of  the  above  types  the  C02H  groups  are  brought 


234 


X.   DIBASIC  ACIDS 


sufficiently  near  to  one  another  for  water  to  be  eliminated, 
and  for  a  closed  ring  to  be  formed  (compare  Polymethylene 
Derivatives). 

The  derivatives  of  the  dibasic  acids,  i.e.  their  esters,  amides, 
&c.,  show  precisely  the  same  characteristics  as  the  analogous 
derivatives  of  the  monobasic  acids,  especially  in  the  readiness 
with  which  they  are  hydrolysed. 

DERIVATIVES  OF  DIBASIC  ACIDS 


Derivatives. 

Salts. 

Esters. 

Chlorides. 

Amides. 

CO-ONa 

CO-OC2H6 

CO  -01 

CO-NH2 

Acid. 

CO-  OH 

Acid  sodium 
oxalate. 

CO-  OH 

Ethyl-oxalic 
acid. 

CO-O(H) 

(only  known  in 
derivatives). 

CO-  OH 

Oxamic 
acid. 

Neutral 
or 
normal. 

CO-ONa 

CO-ONa 

Neutral  sodium 
oxalate. 

CO-OC2H5 

CO-OC,H6 
Ethyl 
oxalate. 

CO-C1 

CO-C1 
Oxalyl 
chloride. 

CO-NH2 

'CO-NH2 

Oxamide. 

As  in  the  case  of  the  glycols,  complications  arise  from  the 
formation  of  mixed  derivatives,  e.g.  partly  ester  and  partly 
amide,  as  in  the  case  of  ethyl  oxamate  (p.  237),  and  also  from 
the  fact  that  many  of  the  acids  form  imides.  Such  imides  are 
derived  from  the  hydrogen-ammonium  salts  of  the  acids  by 
the  elimination  of  two  molecules  of  water,  thus: — 


Succinic  acid 


Succinimide. 


Like  the  amides  they  are  readily  hydrolysed  (cf.  Succini- 
mide). 

Oxalic  acid  (Ethane  diadd),  (C02H)2,  2H20,  is  one  of  the 
oldest  known  organic  acids,  and  occurs  as  its  acid  potassium 
salt  in  many  plants,  especially  in  Oxalis  Acetosella  (wood-sorrel), 
and  in  varieties  of  Rumex,  and  as  the  free  acid  in  varieties  of 
Boletus,  as  normal  sodium  salt  in  varieties  of  Salicornia,  and 
as  calcium  salt  in  rhubarb  root,  &c. 

It  may  be  prepared  by  a  variety  of  different  reactions. 


at  360C 


the  direct  co    bination  of  carbon  dioxide  with  sodium 

04Na2. 


OXALIC  ACID  235 

2.  By   quickly    heating   sodium   formate   to  a  high   tem- 
perature: 2HC02Na  =  H2  +  C204Na2. 


3.  It  is  often  met  with  as  an  oxidation  product  of  relatively 
complex  carbon  compounds,  e.g.  by  the  oxidation  of  alcohol 
by  permanganate,  and  of  sugar,  starch,  wood,  &c.,  by  nitric 
acid.     The  oxidation  of  cane-sugar  with  concentrated  nitric 
acid  is  often  employed  for  the  preparation  of  pure  oxalic  acid. 
The  crystallized   acid   readily  separates  when  the  liquid   is 
cooled  or  evaporated. 

4.  On  the  commercial  scale,  oxalic  acid  is  manufactured  by 
the  fusion  of  cellulose  (see  Carbohydrates)  in  the  form  of  saw- 
dust with  a  mixture  of  sodium  and  potassium  hydroxides  at 
200°-220°  in  flat  iron  pans.    The  sodium  and  potassium  oxalates 
are  extracted  with  water,  then  precipitated  as  calcium  oxalate, 
and  finally  converted  into  the  acid   by  treatment  with  the 
requisite  amount  of  sulphuric  acid. 

It  crystallizes  from  water  in  large,  transparent,  monoclinic 
prisms  containing  two  molecules  of  water  of  crystallization. 
They  slowly  effloresce  in  the  air,  and  readily  become  an- 
hydrous when  heated  at  100°.  At  higher  temperatures  the 
acid  partly  decomposes  into  carbon  dioxide  and  formic  acid, 
and  partly  sublimes  unaltered. 

The  acid  is  readily  soluble  in  water,  moderately  in  alcohol, 
and  somewhat  sparingly  in  ether.  The  aqueous  solution  de- 
composes when  exposed  to  light. 

Concentrated  sulphuric  acid  decomposes  it  into  carbon  mon- 
oxide, carbon  dioxide,  and  water: 


C2H2O4  =  CO2 

Oxalic  acid  is  stable  as  regards  nitric  acid  and  chlorine,  but 
permanganate  of  potash  or  manganese  dioxide  in  acid  solution 
oxidizes  it  to  carbonic  acid: 

C2H204  +  0  =  2C02  +  H2O. 

It  is  reduced  by  nascent  hydrogen  to  glycollic  acid. 

The  strength  of  an  aqueous  solution  of  the  acid  may  bo 
determined  by  titration  with  standard  alkali,  using  phenol 
phthalein  as  indicator,  or  by  means  of  standard  permanganate 
in  the  presence  of  sulphuric  acid. 

Its  salts  are  known  as  oxalates.  The  alkaline  salts,  both  acid 
and  normal,  are  readily  soluble  in  water,  the  normal  sodium 


236  fc.  DIBASIC 

salt  being  the  least  so.  The  "  salt  of  sorrel "  of  commerce  is 
a  mixture  of  C2O4HK  and  a  salt,  C204HK  +  C204H2  +  2H20 
(cf.  p.  144).  The  calcic  salt,  Cs040a  +  H20  (or  3H20),  is 
insoluble  in  water  arid  acetic  acid,  and  serves  for  the  recog- 
nition of  oxalic  acid.  Ferrous-potassic  oxalate,  (C204)2FeK2 
+  H20,  finds  application  in  photography  as  a  powerful  reduc- 
ing agent  (the  "oxalate  developer  ). 

Ethyl  oxalate,  (CO«OC2H6)2,  which  can  be  directly  pre- 
pared from  the  anhydrous  acid  and  ethyl  alcohol  without  a 
catalytic  agent,  is  liquid,  while  methyl  oxalate,  (CO»OCH3)2, 
is  a  solid,  crystallizing  in  plates  which  melt  at  54°;  both  of 
them  possess  an  aromatic  odour,  distil  without  decomposition, 
and  are  extremely  readily  hydrolysed.  Partial  hydrolysis,  with 
alcoholic  potash  solution,  produces  potassium  ethyl-oxalate, 
COOK-COOC2H5,  from  which  the  free  ethyl -oxalic  acid, 
COOH  •  COOC2H5,  which  is  readily  hydrolysed,  and  its 
chloride,  ethyl-oxalyl  chloride,  COC1 .  COOC2H5,  can  easily 
be  prepared.  Oxalic  ester  yields,  with  an  excess  of  ammonia, 
oxamide,  and  with  one  equivalent  the  mixed  derivative,  am- 
monic  oxamate,  COONH4.CQ.NH2. 

Oxalyl  chloride,  (COC1)2,  has  been  obtained  by  the  action  of 
excess  of  phosphorus  pentachloride  on  ethyl  oxalate.  It  is  a 
liquid,  b.-pt.  70°,  and  has  a  pungent  odour  (B.  41,  3558). 

Oxamide,  NH2«CO»CO«NH2,  the  normal  amide  of  oxalic 
acid,  is  obtained,  among  other  methods,  by  the  distillation  of 
ammonium  oxalate,  by  the  partial  hydrolysis  of  cyanogen, 
but  is  most  readily  obtained  by  the  addition  of  ammonium 
hydroxide  solution  to  ethyl  oxalate.  It  is  a  white  crystalline 
powder,  is  readily  hydrolysed,  and  by  the  abstraction  of  water 
may  be  converted  into  cyanogen.  When  heated  it  sublimes 
unchanged. 

Oxamic  acid,  NH2  •  CO  •  CO  •  OH,  the  amic  acid  correspond- 
ing with  oxalic  acid,  is  prepared  by  heating  ammonium  hy- 
drogen oxalate.  It  is  a  crystalline  powder,  sparingly  soluble 
in  cold  water,  possesses  acid  properties,  and  yields  salts,  esters, 
&c.  It  melts  and  decomposes  at  210°. 

Ethyl  oxamate,  oxamethane,  NH2  •  CO  •  CO  •  OC2H5,  is  a  crys- 
talline compound,  and  melts  at  114°-115°.  The  action  of 
PC15  on  this  compound  is  first  to  form  NH2  •  CC12  -  CO  •  OC2H5, 
ethyl-examine  chloride,  which  re,-idily  loses  hydrogen  chlo- 
ride yielding  NH  :  CC1  •  CO  .  OC2H5  and  finally  NjC-Cp. 
OC2H5,  cyano- carbonic  ester.  Corresponding  with  oxamide 
we  have  dimethyl-oxamide,  CH3 .  NH .  CO .  CO .  NHCH3,  and 


MALONICJ  ACID  237 

r 

corresponding  with  oxamethane,  ethyl  -  dimethyl  -  oxamate, 
(CH3)2N  •  CO  •  CO  •  OCgHg,  both  of  which  were  mentioned  at 
p.  106. 


Oximide,  -^NH,  is  prepared  by  the  action  of  PC15  upon 

oxamic  acid.  It  forms  colourless  prisms  readily  soluble  in 
water  and  of  neutral  reaction,  is  quickly  hydrolysed  by  hot 
water,  and  is  transformed  into  oxamide  by  the  action  of  am- 
monia (B.  19,  3228). 

Cyanogen,  N:C-C:N,  is  the  nitrile  corresponding  with  oxalic 
acid  (see  p.  265). 

Malonic  acid,  Propane  diadd,  CH2(C02H)2,  occurs  in  beet- 
root as  its  calcium  salt,  and  may  be  obtained  by  the  following 
methods : — 

^(1)  By  the  oxidation  of  malic  acid  by  means  of  chromic 
acid,  hence  its  name;  (2)  by  the  hydrolysis  of  malonyl-urea 
(p.  288),  (Baeyer}-,  (3)  by  the  hydrolysis  of  cyano-acetic  acid 
(Kolbe,  Milllei-,  A.  131,  348;  204,  121): 

CN.CH2.C02H  +  2H20  =  CH2(CO2H)2  +  NH3. 

It  crystallizes  in  large  plates,  dissolves  readily  in  water, 
alcohol,  and  ether,  melts  at  132°,  and  decomposes  when  heated 
to  a  slightly  higher  temperature. 

Ethyl  malonate,  malonic  ester,  CH2(CO  •  OC2H5)2,  is  usually 
obtained  by  passing  hydrogen  chloride  into  a  solution  of  cyano- 
acetic  acid  (from  chloracetic  acid)  in  absolute  alcohol.  It  is 
a  liquid  of  faint  aromatic  odour  boiling  at  198°,  and  having  a 
remarkable  similarity  to  aceto-acetic  ester.  Thus  the  hydro- 
gen of  the  methylene  group  is  replaceable  by  sodium,  through 
the  influence  of  the  carbonyl  groups  CO,  which  are  also  bound 
to  the  methylene;  and  the  resulting  sodio-malonic  ester  readily 
exchanges  the  metal  for  alkyl  when  treated  with  an  alkyl 
iodide.  By  this  means  the  higher  homologues  of  ethyl 
malonate,  e.g.  methyl-,  ethyl-,  propyl-,  &c.,  malonic  esters,  are 
obtained.  Further,  the  second  hydrogen  atom  in  these  can 
be  exchanged  in  exactly  the  same  manner  for  sodium  and 
then  for  alkyl,  whereby  dialkyl  malonic  acids  are  formed. 
This  so-called  "malonic  ester"  synthesis  is  an  important 
method  for  the  preparation  of  the  higher  dibasic  acids,  being 
applicable  even  in  complicated  cases.  (Cf.  Conrad  and  Bischoff, 
A.  204,  121.)  It  is  also  of  importance  for  the  preparation  of 
some  of  the  higher  fatty  acids,  as  the  substituted  malonic 


238  X.  DIBASIC  ACIDS 

acids  when   heated   above   their  melting-points   lose  carbon 
dioxide  and  yield  fatty  acids: 


When  ethyl  malonate  is  heated  with  its  sodium  compound, 
a  derivative  of  phloroglucinol  is  formed.  (See  this.) 

Malonic  anhydride,  carbon  suboxide,  C302,  0:C:C:C:0, 
is  formed  when  malonic  acid  is  heated  in  a  suitable  apparatus 
at  140°-150°.  (Diels  and  Wolf,  B.  1907,  40,  355;  cf.  also  1906, 
39,  689;  Standinger  and  St.  Bereza,  B.  1908,  41,  4461.)  The 
yield  is  only  10-12  per  cent,  and  acetic  acid  and  carbon  dioxide 
are  also  formed.  It  is  a  colourless  liquid,  b.-pt.  -\-  7°,  m.-pt. 
—  107°,  and  Dj»  I'll.  It  reacts  readily  with  water,  hydrogen 
chloride,  dry  ammonia,  and  aniline,  yielding  respectively  mal- 
onic acid,  malonyl  chloride,  malonamide,  and  malonanilide.  It 
is  stable  at  low  temperatures,  but  decomposes  rapidly  at  100°. 

Succinic  acid,  Butane  diacid,  ethylene-succinic  add,  symmetriwl 
ethane-dicarboxylic  acid  (from  succinum  =  amber),  C02H»CH2- 
CH2«C02H.  This  acid  has  been  known  for  a  long  time;  its 
composition  was  determined  by  Berzelius.  It  exists  in  amber, 
in  various  resins  and  lignites,  in  many  Composite,  in  Papa- 
veraceae,  in  unripe  wine  grapes,  urine,  blood,  &c. 

It  may  be  obtained  by  most  of  the  general  methods  described 
on  p.  231,  e.g.-.  1.  By  the  hydrolysis  of  ethylene  cyanide.  This 
is  an  extremely  important  method,  as  it  affords  a  synthesis  of 
succinic  acid  and  also  establishes  its  constitution,  since  it  can 
be  shown  that  in  ethylene  dibromide  the  two  bromine  atoms 
are  attached  to  distinct  carbon  atoms: 

CH2:CH2  —  CH2Br.CH2Br  —  CN-CHo-CHo-CN 
^*  C02H.CH2.CH2.C02H. 

2.  From  ^-iodo-propionic  acid   by   conversion    first    into 
/5-cyano-propionic  acid  and  subsequent  hydrolysis. 

3.  By  the  reduction  of  f  umaric  and  maleic  acids,  C02H  •  CH  : 
CII-C02H. 

4.  By  heating  its  hydroxy-  acids,   malic  or  tartaric,  with 
hydriodic  acid: 

=  C02H.CH2.CH2.CO2H+I2. 


5.  It  may  also  be  obtained  by  the  fermentation  of  the  salts 
of  these  hydroxy-acids  by  means  of  certain  micro-organisms, 
e.g.  certain  species  of  bacteria, 


SUCCINIO  ACID  239 

It  is  also  formed  in  small  quantities  as  a  by-product  in  the 
alcoholic  fermentation  of  sugar,  and  by  the  oxidation  of  fats, 
fatty  acids,  and  paraffins  by  means  of  nitric  acid. 

It  is  usually  prepared  from  calcic  malate  according  to  5, 
or  by  the  distillation  of  amber. 

6.  It  may  also  be  synthesised  from  ethyl  malonate.  The 
sodio- derivative  of  this  ester  reacts  not  merely  with  alkyl 
iodides  or  bromides,  but  also  with  the  esters  of  haloid  fatty 
acids,  e.g.  ethyl  bromoacetate. 

(C02Et)2CHNa  +  Br.CH2.CO2Et 

=  NaBr  +  (CO2Et)2 .  CH .  CH2 .  CO2Et. 

The  product  is  ethyl  ethane-tricarboxylate,  and  when  this 
is  hydrolysed,  alcohol,  carbon  dioxide,  and  succinic  acid  are 
formed.  This  method  is  of  general  interest,  as  various  sub- 
stituted succinic  acids  may  be  synthesised  by  this  method. 
In  place  of  sodio-ethyl  malonate,  the  sodio-derivatives  of  esters 
of  mono-substituted  malonic  acids  may  be  used,  and  in  place 
of  ethyl  bromo-acetate  the  esters  of  other  halogen  fatty  acids, 
e.g.  ethyl  iodo-propionate  or  ethyl  bromo-valerate.  It  has 
recently  been  shown  (Bone  and  Sprankling,  J.  C.  S.  1899,  839) 
that  better  yields  can  be  obtained  by  using  ethyl  cyano-acetate 
and  its  derivatives  in  place  of  ethyl  malonate  and  its  derivatives. 

Properties. — It  crystallizes  in  monoclinic  prisms  or  plates 
with  an  unpleasant  faintly  acid  taste,  is  readily  soluble  in 
water,  melts  at  185°,  and  boils  at  235°,  but  is  at  the  same 
time  partially  converted  into  its  anhydride.  (For  its  electro- 
lysis, see  pp.  46  and  232.)  Is  very  stable  towards  oxidizing 


Of  the  salts  of  succinic  acid,  the  basic  ferric  salt,  obtained 
by  the  addition  of  a  ferric  salt  to  ammonium  succinate,  is 
used  in  analysis  for  the  separation  of  the  ferric  and  aluminic 
radicals.  The  calcic  salt  is  soluble  in  water. 

The  derivatives  of  succinic  acid  correspond  closely  with 
those  of  oxalic,  e.g.  succinamic  acid,  NH2  •  CO  •  CH2  •  CH2  • 
CO -OH,  is  analogous  to  oxamic  acid,  and  succinamide, 
NH2  •  CO  •  CH2  •  CH2  •  CO  •  NH2,  to  oxamide.  There  also  exists, 
as  in  the  case  of  other  dibasic  acids,  an  imide,  succinimide, 

C2H4<f!c)>NH.  The  latter  crystallizes  in  rhombic  plates, 
and  is  formed  by  heating  ammonium  hydrogen  succinate. 
The  basic  properties  of  the  NH  are  so  modified  by  the  two 
carbonyl  groups  of  the  acid  radical  that  the  imido-hydrogen  is 


240  X.   DIBASIC  ACIDS 

replaceable  by  metals,  such  as  K,  Ag,  &c.     (Cf.  B.  25,  Kef. 
283.)     Succinyl  chloride  reacts  as  though  it  were  dichloro- 


butyro-lactone,    C2H4^QQ_^>0.      It  is   a   colourless   liquid 

boiling  at  190°,  and  is  obtained  by  the  action  of  phosphorus 
pentachloride  (2  mols.)  on  the  acid,  or  of  1  mol.  on  the  anhy- 
dride. In  many  of  its  properties  it  resembles  the  acid  chlorides, 
but  on  reduction  yields  butyro-lactone  ;  with  benzene  and  alu- 
minium chloride  it  yields  mainly  y-diphenyl-butyro-lactone, 

PPh 

,  and  with  zinc  ethyl  y-diethyl-butyro-lactone. 


The  chloride  is  probably  a  mixture  of  dichloro-butyro-lactone 
with  a  small  amount  of  the  normal  chloride.  Succinic  an- 

PO 
hydride,  C2H4<^pQ^>0,  is  best  obtained  by  the  action  of  acetic 

anhydride  on  the  acid.  It  crystallizes  in  glistening  plates, 
melts  at  120°,  and  distils  without  decomposition.  It  slowly 
combines  with  water,  yielding  the  acid;  more  readily  with 
alkalis,  and  also  with  alcohols  at  a  higher  temperature,  yield- 
ing the  acid  esters,  e.g.  HO.CO-CH2.CH2.CO.OEt.  This  is 
the  most  convenient  method  for  the  preparation  of  acid  esters. 
The  other  methods  sometimes  employed  are:  (a)  the  partial 
hydrolysis  of  the  neutral  ester,  and  (b)  the  partial  esterifi- 
cation  of  the  acid  by  means  of  very  dilute  solution  of  hydrogen 
chloride  in  the  requisite  alcohol  (Bone,  Sudborough,  and  Spunk- 
ling,  J.  C.  S.  1904,  534). 

Of  the  higher  acids  the  following  are  of  interest  :  — 
Glutaric  acid,  Pentane  diacid,  C02H-CH2.CH2.CH2.C02H. 
—  It  may  be  obtained  from  glutamic  acid  (p.  249),  and  also  by 
condensing  formaldehyde  with  ethyl  malonate  in  the  presence 
of  a  small  amount  of  diethylamine  : 

CH2:O  +  2H-CH(C02Et)2 

(CO2Et)2.CH.CH2.CH(CO2Et)2. 


This  is  a  further  example  of  the  readiness  with  which  alde- 
hydes condense  with  compounds  containing  a  methylene  group 
adjacent  to  carbonyl  or  negative  groups.  The  product,  ethyl 
propane-tetracarboxylate,  on  hydrolysis  yields  ethyl  alcohol, 
carbon  dioxide,  and  glutaric  acid.  The  last  crystallizes  in 
prisms,  melts  at  97°,  is  readily  soluble  in  water,  and  yields 
an  anhydride,  an  imide,  &c.  The  imide  can  be  obtained 
when  piperidine  is  oxidized  with  hydrogen  peroxide,  and  when 
distilled  with  zinc  dust  yields  a  small  amount  of  pyridine, 


UNSATURATED  DIBASIC  ACIDS  241 

Isomeric  with  glutaric  acid  is  methyl-succinic  or  pyro- 
tartaric  acid,  C02H  .  CHMe  •  CH2  •  C02H,  an  acid  closely 
resembling  succinic  acid,  and  obtained  by  dry  distillation  of 
tartaric  acids. 

The  s-  dimethyl-  and  s-dibromo-  succinic  acids,  C02H» 
CHBr'CHBr»C02H,  occur  in  the  same  number  of  stereo- 
isomeric  modifications  as  the  tartaric  acids  (p.  249). 

Mono-  and  dibromo-succinic  acids,  C2H3Br(C02H)2  and 
C2H2Br2(C02H)2,  are  easily  prepared,  and  are  valuable  for  the 
syntheses  of  the  hydroxy-succinic  acids. 

Sodium  reacts  with  ethyl  succinate,  yielding  ethyl  succinylo- 
succinate,  a  compound  related  to  benzene. 

Isosuccinic  acid,  Methyl  -  propane  diacid,  ethylidene  -  succinic 
add,  or  methyl -malonic  acid,  CH3  •  CH(C02H)2,  is  formed  by 
the  malonic  ester  synthesis,  or  from  a-chloro-  (or  iodo-)  pro- 
pionic  acid  (pp.  237  and  232).  It  is  a  solid,  when  heated 
decomposes  into  C02  and  propionic  acid,  and  yields  no  an- 
hydride (p.  234). 

Relative  strengths  of  the  dibasic  acids: 

K 

Oxalic 10-0  (about) 

Malonic 0'163 

Succinic 0'0066 

Glutaric 0'0047 

The  strengths  of  alkylated  succinic  acids  are  not  so  very 
different  from  that  of  succinic  acid,  and  those  of  alkyl  glutaric 
acids  are  of  the  same  order  as  that  of  glutaric. 

B.  Unsaturated  Dibasic  Acids 

The  unsaturated  acids  stand  in  the  same  relation  to  the 
saturated  dibasic  acids  as  acrylic  acid  does  to  propionic.  As 
dibasic  acids  they  yield  derivatives  analogous  to  those  of  oxalic 
acid,  while  as  unsaturated  compounds  each  molecule  possesses, 
in  addition,  the  property  of  combining  with  two  atoms  of  hy- 
drogen or  halogen,  or  with  one  molecule  of  halogen  hydride. 

Common  Methods  of  Formation. — 1.  By  the  elimination  of 
water  from  the  hydroxy  dibasic-acids.  Thus  malic  acid  when 
distilled  yields  water  and  maleic  anhydride,  which  volatilizes, 
and  also  fumaric  acid,  which  remains  behind : 

CO2H.CH(OH).CH2.CO2H  -  H2O  =  CO2H.CH:CH.CO2H. 

The  actual  product  obtained  by  the  elimination  of  water 

(U480)  Q 


242  X.   DIBASIC   ACIDS 

from  malic  acid  varies  considerably  with  the  conditions  of 
the  experiment.  Thus,  when  malic  acid  is  maintained  at  a 
temperature  of  140°-150°  for  some  time,  the  chief  product  is 
fumaric  acid;  when  the  malic  acid  is  rapidly  -heated  at  a 
higher  temperature,  maleic  anhydride  is  largely  formed. 

Citric  acid  yields,  in  a  similar  way,  C02,  H20,  itaconic  acid, 
CH2:C(C02H).CH2.C02H,  and  citraconic  anhydride  (methyl- 
maleic  anhydride). 

2.  By  the  separation  of  halogen  hydride  from  the  mono- 
haloid  derivatives  of   succinic  acid  arid  its  homologues,  e.g. 
monobromo-succinic  acid  yields  fumaric,  thus: — 

CO2H.CHBr.CH2.CO2H-HBr  =  CO2H.CH:CH.CO2H. 

3.  Fumaric   acid   has   been    prepared    synthetically    from 
acetylene  di-iodide,  just  as  succinic  acid  has  been  from  ethy- 
lene  dibromide. 

Constitution. — The  acids  of  this  series  may  be  regarded  as 
dicarboxylic  acids  of  the  olefines,  e.g.  fumaric  and  maleic  acids, 
C2H2(C02H)2,  as  those  of  ethylene.  Their  mode  of  formation 

1  corresponds  exactly  with  the  production  of  ethylene  from 
alcohol,  or  with  that  of  acrylic  from  ethylene  lactic  acid,  while 

2  agrees  with  that  of  ethylene  from  ethyl  iodide. 

Maleic  acid  (ds-Butene  diacid),  C02H.CH:CH.C02H,  crys- 
tallizes in  large  prisms,  possesses  a  grating,  nauseous  acid 
taste,  and  is  very  readily  soluble  in  cold  water.  It  distils 
unchanged,  excepting  for  partial  transformation  into  maleic 
anhydride.  It  is  conveniently  prepared  by  heating  the  acetyl 
derivative  of  malic  acid  (see  p.  247),  or  from  fumaric  acid  and 
POC18  (A.  268,  255). 

Fumaric  acid  (trans-Butene  diacid),  C2H2(C02H)2,  crystallizes 
in  small  prisms  with  a  strong,  purely  acid  taste,  and  is  almost 
insoluble  in  cold  water.  It  does  not  melt,  but  sublimes  at  about 
200°  with  formation  of  maleic  anhydride.  It  occurs  in  Fumaria 
offidnalis,  various  fungi,  truffles,  Iceland  moss,  &c.,  and  is 
obtained  from  maleic  acid  either  by  prolonged  heating  of  the 
latter  at  130°,  or  by  the  action  upon  it  of  hydrobromic  or 
other  acids.  (For  its  preparation,  see  A.  268,  255.) 

Both  acids  are  converted  into  esters  when  their  silver  salts 
are  heated  with  alkyl  iodide,  and  these  esters  stand  in  very 
close  relationship  to  one  another,  as  do  the  free  acids;  thus 
ethyl  maleate  is  changed  into  ethyl  fumarate  when  warmed 
with  iodine,  and  the  latter  ester  is  formed  by  saturating  an 
alcoholic  solution  of  maleic  acid  with  dry  hydrogen  chloride. 


STEREO-CHEMISTRY   OF  UNSATURATED   DIBASIC   ACIDS      243 

Isomerism  of  Funiaric  and  Maleic  Acids.— The  isomerism 
of  these  two  acids  is  a  problem  which  has  attracted  the  atten- 
tion of  numerous  chemists.  Attempts  were  first  made  to 
account  for  the  difference  by  polymerism  or  structural  iso- 
merism, e.g.  Fittig  has  suggested 

CO2H.CH:CH.CO2H    and    C02H.CH2.C-C02H; 

A 

but  isomerism  of  this  type  is  impossible,  since  both  acids 
when  oxidized  yield  one  or  other  of  the  tartaric  acids  C02H  • 
CH(OH)  •  CH(OH) .  C02H. 

Anschutz  has  brought  forward  the  formulae 

CH-CO , 

CO2H.CH:CH.CO2H    and     ||  >O. 

CH.C(OH)/ 

Such  a  formula  as  the  latter  is  not  at  all  probable,  as  in  this 
case  maleic  acid,  which  is  the  stronger  acid  (K  =  1'17,  and 
for  fumaric  K  =  0'093),  would  not  possess  a  carboxylic,  but 
merely  a  hydroxy  lactone  structure  (PFegscheider,  B.  1903, 
36,  1543).  This  formula  is  also  found  to  be  quite  unten- 
able when  the  products  of  bromi  nation  and  of  oxidation  are 
considered. 

The  fact  that  the  two  acids  are  structurally  identical,  and 
must  both  be  represented  as  ethylene  dicarboxylic  acids,  is  now 
generally  recognized,  and  the  conclusion  is  largely  based  on 
the  following  facts: — (1)  Both  acids  when  reduced  with 
sodium  amalgam  yield  ordinary  succinic  acid.  (2)  Both  acids 
combine  with  hydrogen  bromide,  yielding  the  same  bromo- 
succinic  acid.  (3)  Both  acids  combine  with  water  at  moderate 
temperatures,  yielding  the  same  malic  acid.  In  most  of  these 
additive  reactions  the  maleic  acid  reacts  somewhat  more  readily 
than  the  fumaric,  and  is  at  the  same  time  partially  transformed 
into  fumaric.  (4)  When  carefully  oxidized,  the  two  acids 
yield  stereo-isomeric  tartaric  acids,  maleic  being  transformed 
into  meso-tartaric,  and  fumaric  into  racemic  acid.^  (5)  Simi- 
larly, on  addition  of  bromine  they  yield  stereo-isomeric  di- 
bromo-succinic  acids. 

As  the  two  acids  are  structurally  identical,  the  isomerism 
can  only  be  accounted  for  by  a  different  spatial  relationship 
of  the  atoms  within  the  molecule.  The  stereo-isomerism  of 
these  unsaturated  compounds  is  quite  distinct  from  that  of 
the  saturated  compounds,  such  as  lactic  and  tartaric  acids. 


244  X.   DIBASIC  ACIDS 

We  are  forced  to  assume  that  in  saturated  compounds  where 
two  C  atoms  are  united  by  a  single  bond,  there  is  free  rotation 
around  the  axis  represented  by  the  bond;  otherwise,  the 
number  of  isomerides  Cabc-Cdef,  or  even  Caab-Caab, 
would  be  much  greater  than  what  is  actually  found.  When, 
however,  the  two  carbon  atoms  become  united  by  a  so-called 
double  bond,  free  rotation  is  completely  prevented,  and  we 
have  the  centres  of  gravity  of  the  two  C  atoms  and  of  the 
four  substituents  all  lying  in  the  same  plane,  viz.  the  plane 
of  the  paper,  e.g.  C2H4  may  be  represented  as 

H-C-H 

H.C.H. 

No  stereo-isomerism  is  possible  with  such  a  compound,  nor 
yet  with  any  compound  in  which  the  2  radicals  attached  to 
the  one  carbon  atom  are  the  same,  e.g.  CH2:CC1«C02H;  but 
immediately  each  carbon  atom  has  2  different  radicals  attached 
to  it,  isomerism  is  theoretically  possible,  e.g.  crotonic  acid, 
CH3.CH:CH.C02H,  and  maleic  acid,  C02H . CH : CH . C02H, 
viz.: 

CH3.C-H  CH3.C-H 

C02H.C.H  H.C.C02H, 

C02H-C.H  C02H.C.H 

C02H.C.H  H.C.C02H; 

and  similarly  for  oleic  and  elaidic  acids,  erucic  and  brassidic 
acids,  cinnamic  and  allocinnamic  acids  and  its  derivatives,  and 
also  for  numerous  other  compounds. 

As  the  centres  of  gravities  of  the  carbon  atoms  and  of  their 
substituents  all  lie  in  one  plane,  the  molecules  are  not  perfectly 
asymmetric,  and  therefore  possess  no  optical  activity,  and 
cannot  be  resolved  into  optically  active  components. 

The  two  isomerides  are  not  so  closely  related  to  one  another 
as  d-  and  /-valeric  acids,  or  as  d-  and  Z-tartaric  acids;  as  a  rule, 
they  differ  entirely  as  regards  their  ordinary  physical  pro- 
perties, e.g.  crystalline  form,  solubility,  melting-point,  water 
of  crystallization,  dissociation  constant,  &c.,  and  in  many  cases 
considerable  differences  in  chemical  properties  are  met  with, 
e.g.  maleic  acid  yields  an  anhydride  and  fumaric  acid  does  not. 
As  a  rule,  one  of  the  isomerides  is  less  stable  than  the  other, 
and  under  suitable  conditions,  e.g.  influence  of  (a)  heat, 


STEREO-CHEMISTRY   OF  UNSATURATED  DIBASIC  ACIDS      245 

(b)  light,  (c)  chemical  reagents,  especially  small  amounts  of 
halogens  or  halogen  hydracids,  the  labile  compound  is  trans- 
formed into  the  stable.  With  certain  pairs  of  isomerides  the 
transformation  is  mutual,  so  that  whichever  of  the  two  we 
start  with  we  obtain,  under  the  conditions  enumerated  above, 
a  mixture  of  the  two  in  chemical  equilibrium. 

As  examples  of  the  transforming  action  of  heat  we  have  the 
following :— Fumaric  -*  maleic;  allocinnamic  —  cinnamic; 
angelic  —  tiglic,  and  either  chloro-fumaric,  C02H-CC1:CH. 
C02H,  or  chloro-maleic  acid  heated  separately  yields  a  mixture 
of  the  two.  The  effect  of  exposure  to  sunlight  is  often  identical 
with  the  action  of  heat,  but  not  always  so,  e.g.  ethyl  benzyl- 

aminocrotonate,    QH  ph  ^ -^ j|^>C :  CH  •  C02Et,    exists   in   two 

stereo-isomeric  modifications  melting  at  79°  and  21°;  the  effect 
of  heat  is  to  transform  the  higher  melting  ester  into  the  lower 
melting,  and  the  effect  of  sunlight  is  the  exact  opposite.  As 
examples  of  the  influence  of  chemicals,  we  have  the  action 
of  small  amounts  of  nitrous  acid  in  transforming  oleic  into 
elaidic  and  erucic  into  brassidic  acids.  Similarly,  small 
amounts  of  bromine  will  transform  dimethyl  maleate  into 
dimethyl  fumarate. 

Skraup  has  shown  that  either  sulphur  dioxide  or  hydrogen 
sulphide  alone  is  unable  to  transform  maleic  into  fumaric,  but 
that  a  mixture  of  the  two  will  bring  about  the  transformation. 
The  chemical  reaction  between  the  H2S  and  S02  may  be  re- 
garded as  a  type  of  detonator  which  starts  the  transformation 
in  the  maleic  acid.  All  chemical  reactions,  however,  cannot 
act  in  the  same  manner  as  catalysts.  It  has  also  been  shown 
that  the  salts  of  maleic  acid,  e.g.  copper  maleate,  when  decom- 
posed by  hydrogen  sulphide  yield  fumaric  acid  or  a  mixture 
of  fumaric  and  maleic  acids,  although,  as  stated  above,  the 
sulphide  itself  is  incapable  of  transforming  free  maleic  acid 
into  fumaric. 

The  exact  method  of  transformation  is  not  known.  It  may 
be  (a)  that  the  two  radicals  attached  to  the  one  carbon  atom 
actually  exchange  positions  directly;  (b)  the  two  carbon  atoms 
may  not  be  entirely  unable  to  rotate  round  their  common 
axis,  but  may  only  be  in  a  state  of  strain,  and  under  the 
influence  of  light,  heat,  &c.,  a  rotation  through  an  angle  of 
180°  may  occur;  or  (c)  in  the  case  of  change  brought  about  by 
chemical  agents  it  is  possible  that  the  agent  employed  first 
forms  an  additive  compound  and  is  subsequently  removed, 


246  X.   DIBASIC  ACIDS 

but  this  view  has  been  shown  to  be  impossible  in  many  cases 
by  Anschiitz,  Fittig,  and  Michael. 

The  system  of  nomenclature  adopted  to  distinguish  between 
the  two  isomerides  is  to  term  the  compound  in  which  two 
similar  substituents  are  on  the  same  side  of  the  molecule  the 
cis  compound,  and  the  isomeride  in  which  the  two  similar 
radicals  are  on  opposite  sides  of  the  molecule  the  trans: 

C02H.C-H  C02H.C-H 

C02H.C-H  H.C.C02H 

cw-Ethylene  dicarboxylic  acid       trans-Ethylene  dicarboxylic  acid. 

In  cases  where  it  has  not  been  found  possible  to  ascertain 
which  of  the  two  known  compounds  has  the  cis  configuration 
and  which  the  trans,  the  ordinary  name  is  given  to  the  one 
and  the  prefix  iso,  or  better,  allo,  to  the  other,  e.g.  crotonic  and 
isocrotonic  acids,  cinnamic  and  allocinnamic  acids. 

Determination  of  Configuration. — In  the  case  of  fumaric  and 
maleic*  acids  this  has  been  accomplished  with  a  considerable 
degree  of  certainty.  The  arguments  used  for  the  cis  con- 
figuration of  maleic  and  the  trans  configuration  of  fumaric  are 
briefly :  (a)  Maleic  acid  when  heated,  or  treated  with  dehydrat- 
ing agents,  readily  yields  an  anhydride  (cf.  Succinic  anhydride), 

CH-CCK 

/>0,  which  can  combine  with  water  to  re-form  maleic 

acid.  Fumaric  acid  yields  no  distinct  anhydride  of  its  own. 
(b)  Maleic  acid  when  oxidized  yields  meso-tartaric  acid,  whereas 
fumaric  acid  yields  racemic  acid  (see  p.  252) : 

CO2H 

H.C.C02H  H-j-OH 

H.n.C02H  H4-OH 

C02H. 

CO2H  CO2H 

H.C.C02H  HfOH       d  OH-J-H 

C02H.C.H  C02H-M)E  OH-f(X)2H 


Th3  configurations  of  other  pairs  of  olefine  stereo-isomerides 
have  not  been  determined  with  the  same  degree  of  certainty, 
and  many  of  the  methods  described  in  text-boots  as  being 
available  for  this  purpose  cannot  be  relied  on,  e.g.  of  two 


HYDftOXY  DIBASIC  ACIDS  247 

stereo-isomeric  a-  or  /Mialogenated  compounds,  the  one  which 
has  the  halogen  in  the  czs-position  with  respect  to  a  hydrogen 
atom  will  lose  halogen  hydracid  more  readily  under  the 
influence  of  alkali,  e.g.  : 

CH3.C.Br  CH3.C.Br 

H.C.C02H 


In  many  cases  it  is  probable  that  exactly  the  reverse  holds 
good. 

An  admirable  account  of  the  stereochemistry  of  olefine 
derivatives  will  be  found  in  Werner's  "  Stereochemie  ",  1904 
pp.  179-227. 

For  higher  homologues,  see  Fittig,  B.  26,  40. 

Acetylene-dicarboxylic  acid,  Butine  diacid,  C02H«C:C' 
C02H,  is  a  type  of  an  acetylenic  acid;  it  is  obtained  by  the 
elimination  of  two  molecules  of  hydrogen  bromide  from  one  of 
dibromo-succinic  acid.  It  possesses  the  characteristic  proper- 
ties of  a  dibasic  acid,  and  also  of  an  unsaturated  compound, 
but  does  not  yield  metallic  derivatives  of  the  type  of  silver 
acetylene.  It  readily  loses  carbon  dioxide,  yielding  propargylic 
acid,  CH:C-C02H.  Diacetylene-dicarboxylic  acid,  C02H- 
C:C'CiC»C02H,  and  tetracetylene-dicarboxylic  acid,  Deca- 
tetrine  diacid,  C02H  .CiC-CiC-CiC-CiO.  C02H,  have  been 
prepared  by  Baeyer  (B.  18,  678  and  2269).  With  increasing 
length  of  chain  they  show  an  increasing  tendency  to  explode. 
(For  Baeyet's  theory  of  explosions,  see  B.  18,  2277.) 

C.  Hydroxy  Dibasic  Acids 

1.  Tartronic  acid,  Propanol  diacid,  hydroxy-malonic  acid,  OH- 
CH.(C02H)2,  forms   large   prisms   (-f  ^H20),  and   is  ^  easily 
soluble  in  water,  alcohol,  and  ether.     It  cannot  be  distilled 
unchanged,  since  it  breaks  up  on  heating  into  carbon  dioxide 
and  glycolide.     As  hydroxy-malonic  acid  it  may  be  prepared 
by  the  action  of  moist  silver  oxide  on  chloromalonic  acid.     It 
may  also  be  obtained  by  the  reduction  of  the  corresponding 
ketonic  acid,   mesoxalic  acid,  CO(C02H)2,  and  also  by  the 
oxidation  of  glycerol  with  permanganate. 

2.  Malic  acid,  Butanol  diacid,  hydroxy-succinic  acid,  C02H- 
CH2.CH(OH).COJS  (Scheele,  1785),  is  very  widely  distributed 
in  the  vegetable  kingdom,  being  found  in  unripe  apples,  sorb- 
apples,  grapes,  barberries,  mountain-ash  berries,  quinces,  &c. 


248  X.   DIBASIC  ACIDS 

Some  of  the  simpler  methods  of  formation  are  quite  analogous 
to  those  employed  in  the  case  of  hydroxy  monobasic  acids,  e.g. 

(1)  by  the  action  of  moist  silver  oxide  on  bromo-succinic  acid; 

(2)  by  the  reduction  of  tartaric  or  racemic  acid  with  HI,  and 
of  oxal-acetic  acid  (pp.  224  and  260)  with  sodium-amalgam; 

(3)  by  the  action  of  nitrous  acid  on  the  corresponding  amino 
acid,  aspartic  acid;  and  (4)  by  the  addition  of  the  elements  of 
water  to  fumaric  or  maleic  acid  under  the  influence  of  aqueous 
sodic  hydroxide. 

It  crystallizes  in  hygroscopic  needles,  is  readily  soluble  in 
water  and  alcohol,  but  only  sparingly  in  ether.  It  melts  at 
100°,  and  when  it  is  distilled,  maleic  anhydride  passes  over 
and  fumaric  acid  remains  in  the  retort  (p.  241).  K  =  0'04. 

The  molecule  of  malic  acid  contains  an  asymmetric  carbon 
atom,  and  thus  the  acid  should  exist  in  two  optically  active 
and  a  racemic  modification.  The  acid  obtained  from  natural 
sources,  Z-malic  acid,  is  Ia3vo-rotatory  in  dilute  solution,  but  the 
rotation  diminishes  as  the  concentration  increases.  With  a 
34-per-cent  solution  at  20°  no  optical  activity  is  shown,  and  with 
more  concentrated  solutions  dextro-rotation  is  exhibited.  The 
acid  obtained  synthetically  is  optically  inactive  and  constitutes 
the  racemic  form,  and  it  has  been  resolved  into  optically  active 
modification  by  the  usual  methods  (p.  254),  (B.  1898,  31,  528). 

The  alkali  salts  and  the  acid  calcium  salt  of  malic  acid  are 
readily  soluble  in  water,  while  the  normal  calcium  salt  is  only 
sparingly  soluble. 

The  constitution  follows  from  its  methods  of  preparation, 
from  the  fact  that  it  is  readily  reduced  to  succinic  acid,  and 
that  its  esters  react  with  acetic  anhydride,  yielding  mono- 
acetyl  derivatives. 

Amides  and  Amines  of  Malic  Acid. — Like  glycollic  acid, 
malic  acid  forms — as  an  acid — amides  (saponifiable),  and — as 
an  alcohol — an  amine  (not  saponifiable).  The  amides  are: — 

Malamide,  NH2.CO.CH(OH).CH2.CO.NH2,  crystallizing 
in  prisms,  and  malamic  acid,  C02H.CH2.CH(OH).Cp-NH2, 
the  latter  being  only  known  as  ethyl  ester.  The  amino-acid, 
aspartic  acid,  C02H  •  CH(NH2)  -  CH2  •  CO2H,  unites  in  itself, 
like  glycocoll,  the  properties  of  a  base  and  of  an  acid,  but 
the  acid  character  predominates.  Its  acid  amide,  asparagine, 
CO2H.CH(NH2).CH2.CO.NH2,  which  is  isomeric  with  mal- 
amide,  is  very  widely  distributed  in  the  vegetable  kingdom, 
being  present  in  the  young  leaves  of  trees,  in  beet-root, 
potatoes,  the  shoots  of  peas,  beans,  and  vetches,  and  in 


ASPARTIC  ACID.      TARTARIC  ACID  249 

asparagus;  it  was  first  found  in  the  last-named  vegetable  in 
the  year  1805.  It  forms  glistening  rhombic  prisms  (+  H20), 
is  readily  soluble  in  hot  water,  but  insoluble  in  alcohol  and 
ether,  and  yields  aspartic  acid  when  hydrolysed.  It  is  leevo- 
rotatory. 

A  dextro-rotatory  asparagine  has  likewise  been  obtained 
from  the  shoots  of  vetches  (B.  20,  Ref.  510);  it  possesses  a 
sweet  taste,  and  unites  with  the  laevo-rotatory  compound  to 
an  inactive  modification.  For  the  synthesis  of  the  asparagines 
and  their  constitution,  see  Piutti,  B.  22,  Ref.  241  and  243. 

Aspartic  acid,  amino-succinic  add,  is  present  in  beet  molasses, 
and  forms  an  important  product  of  the  decomposition  of 
proteids  with  acids  or  alkalis.  It  has  been  synthesized,  e.g. 
from  bromo-succinic  acid  and  ammonia,  and  crystallizes  in 
small  rhombic  plates  readily  soluble  in  hot  water.  It  exists 
in  optically  active  modifications,  which  differ  in  taste  and 
are  convertible  the  one  into  the  other  (B.  20,  R.  510). 
Nitrous  acid  transforms  both  aspartic  acid  and  asparagine 
into  malic  acid. 

Glutainic  acid,  a-amino-glutaric  acid,  C02H  •  CH(NH2)  •  CH2  • 
CH2^C02H,  and  glutamine  correspond  with  aspartic  acid  and 
asparagine.  The  former  is  found  in  beet-root  and  in  the 
shoots  of  the  vetch  and  gourd,  while  the  latter  is  produced, 
together  with  aspartic  acid  and  leucine,  by  boiling  proteids 
with  dilute  sulphuric  acid. 

D.  Dihydroxy  Dibasic  Acids 

These  acids  are  characterized  by  the  presence  of  two  hy- 
droxyl  radicals  in  the  molecule  in  addition  to  two  carboxyls. 

Tartaric  acid,  Butane  -diol  diacid,  dihydroxy  -  succinic  add, 
C02H  .  CH(OH) .  CH(OH)  •  (C02H),  exists  in  four  distinct 
modifications. 

1.  d-  or  Dextro-tartaric  acid,  m.-pt.  170°. 

2.  /-  or  Laevo-tartaric  acid,  anti-tartaric  add,  m.-pt.  170°. 

3.  Racemic  acid,  d-l-tartaric  add,  para-tartaric  add,  m.-pt. 
206°. 

4.  i-  or  Inactive  tartaric  acid,  meso-tartaric  add,  m.-pt.  143°. 

The  constitution  of  these  acids  follows  from  their  relation- 
ship to  succinic  acid,  from  their  methods  of  formation,  and 
from  the  fact  that  their  esters  with  acetic  anhydride  yield 
diacetyl  derivatives. 

Solutions  of  equal  concentration  of  the  two  first  of  these 


250  X.    DIBASIC  ACIDS 

acids  turn  the  plane  of  polarization  of  light  in  an  equal 
degree,  but  in  opposite  directions.  By  their  union  the  in- 
active racemic  acid  is  formed,  and  this  can,  conversely,  bo 
separated  into  its  components.  The  fourth  tartaric  acid, 
likewise  inactive,  cannot  be  resolved  in  this  way. 

The  common  tartaric  acid  found  in  nature  is  optically 
active,  and  is  the  ^-tartaric  acid,  whereas  the  acids  obtained 
synthetically  are  optically  inactive,  viz.  racemic  acid  or  meso- 
tartaric  acid,  or  a  mixture  of  both,  e.g.  dibromo-succinic  acid 
with  moist  silver  oxide  yields  a  mixture  of  racemic  and  meso- 
tartaric  acids. 

Fumaric  acid  when  oxidized  with  permanganate  is  converted 
into  racemic  acid,  and  maleic  acid  by  a  similar  process  into 
meso-tartaric  acid  (p.  246).  Glyoxal  cyanhydrin  (p.  221)  when 
hydrolysed  yields  racemic  acid,  and  finally,  mannitol  when 
oxidized  with  nitric  acid  yields  racemic  acid,  and  sorbitol 
meso-tartaric  acid. 

Synthesis  : 

CH2:CH2  —  -  CH2Br.CH2Br  —  -  CN.CH2.CH2-CN 
Br  KCN 


—  C02H.CHBr.CHBr.C02H 
Hydrolysis  Br2 

—  C02H.CH(OH).CH(OH).C02H. 
AgOH 

Stereo-isomerism  of  the  Tartaric  Acids.  —  The  isomerism  of 
the  tartaric  acids  is  of  much  the  same  type  as  that  discussed 
in  the  case  of  active  valeric  and  of  a-lactic  acid.  A  glance  at 
the  constitutional  formula  for  the  acids  shows  the  presence  of 
2  asymmetric  carbon  atoms;  to  each  of  these  2  atoms  are 
attached  the  radicals  H,  OH,  and  C02H,  and  the  remaining 
valency  of  each  carbon  is  employed  in  attaching  it  to  the  other 
carbon  atom. 

A  compound  of  this  general  type,  C(a,  b,  c)  •  C(a,  b,  c),  is 
known  as  a  compound  containing  2  similar  asymmetric  carbon 
atoms.  If  one  valency  of  each  carbon  is  employed  in  uniting 
the  2  carbon  atoms  together,  then  the  3  radicals,  a,  b,  c,  which 
are  attached  to  the  remaining  three  valencies  of  a  carbon  atom, 

may  be  arranged  in  two  distinct  ways,  viz.  a~^    ,  positive  order, 
and    V'  ,  negative  order. 


STEREO-CHEMISTRY  OF  TARTARIC  ACIDS 
The  following  combinations  are  thus  possible:  — 


251 


But  Nos.  3  and  4  must  be  identical,  as  the  radicals  attached 
to  the  2  asymmetric  carbon  atoms  are  identical. 
These  spatial  relationships  may  be  represented: 


where  a  =   H,  b  =  OH,  and  c  =  C02H. 

Note. — At  first  sight  it  appears  as  though  the  radicals  a,  b,  c 
in  the  lower  half  of  fig.  1  were  arranged  in  the  —  and  not  the 
-f-  order,  as  indicated.  It  must  be  remembered,  however,  that 
each  part  of  the  molecule  must  be  looked  at  from  the  same 
point  of  view;  and  if  we  take  the  order  of  the  radicals  in  the 
upper  tetrahedron  when  arranged  so  that  the  solid  angle 
which  represents  the  point  of  attachment  to  the  second  tetra- 
hedron is  pointed  down,  then  we  must  regard  the  second 
tetrahedron  from  the  same  point  of  view,  i.e.  we  must  turn 
the  figure  upside  down.  It  is  then  seen  that  the  arrangement 
in  the  lower  half  of  the  molecule  is  the  -f . 

Instead  of  using  the  above  cumbrous  figures,  it  is  usual  to 
regard  such  models  as  projected  upon  a  plane  surface,  and  to 
use  the  projections  thus  obtained  (E.  Fischer,  B.  1891, 24,  2684): 


a— C-b 
u— C— a 


\y 

)_C— a  b— C— a 

Jw 


a— U— b 

i 
e 


I 
b— C-a 

I 

e 


252  X.   DIBASIC  ACID8 

or  c  c 


a-Lb  b-fa  b-U 

b-U  a-Lb  b-L-a 


Note. — The  manner  in  which  these  projection  formulae  are 
obtained  can  be  best  seen  by  means  of  models. 

A  comparison  of  the  three  configurations  at  once  shows  that 
Nos.  I  and  II  are  perfectly  asymmetric,  and  are  related  to 
one  another  as  object  to  mirror  image;  they  should  therefore 
represent  the  two  optically  active  tartaric  acids,  and  the 
compound  of  the  two  should  represent  the  molecule  of  racemic 
acid.  No.  Ill  has  a  plane  of  symmetry,  and  should  therefore 
represent  the  non-resolvable,  inactive  acid — meso-tartaric  acid. 

The  question  as  to  whether  No.  I  represents  d-  or  /-tartaric 
acid  has  been  settled  by  Fischer  (B.  1896,  29,  1377)  in  favour 
of  the  d-acid.  We  thus  have : 

CO2H  CO2H  CO2H 

H-[-OH  OH-Ln  OH-j-H 

OH-j-H  H-K)H  OH-f-H 

C02H  C02H  C02H 

d  I  meso 

1.  Dextro-tartaric  acid,  acidum  tarlaricum,  is  the  tartaric 
acid  found  in  nature.  It  was  discovered  by  Scheele  in  1769. 
It  occurs  in  the  free  state,  but  chiefly  as  acid  potassium  salt, 
in  various  fruits,  especially  in  the  juice  of  grapes,  from  which 
potassic  hydric  tartrate  (cremor  tartari)  separates  in  crystals 
during  fermentation.  When  this  is  boiled  with  chalk  and 
chloride  of  calcium  it  is  transformed  into  the  neutral  calcium 
salt,  from  which  the  acid  is  liberated  on  addition  of  H2S04. 

It  crystallizes  from  water  in  large  transparent  monoclinic 
prisms,  of  a  strong  and  purely  acid  taste,  is  readily  soluble  in 
water,  also  in  alcohol,  but  almost  insoluble  in  ether.  It  melts 
at  170°,  and  its  aqueous  solution  reduces  an  ammomacal  silver 
solution  upon  warming.  When  melted,  it  is  changed  into  an 
amorphous  modification,  and  then  into  an  anhydride,  and  when 
heated  more  strongly  it  carbonizes  with  the  dissemination  of 
a  characteristic  odour  and  formation  of  pyro-racemic  and  pyro- 
tartaric  acids.  Oxidation  converts  it  either  into  dihydroxy- 
tartaric  (p.  260)  or  tartronic  acid,  and  then  into  formic  and 
carbonic  acids,  &c.  It  is  employed  in  medicine,  dyeing,  &c. 


TARTARIC   ACID   DERIVATIVES  253 

Normal  potassic  tartrate,  C4H406K0  +  JH2O,  forms  mono- 
clinic  prisms  easily  soluble  in  water.  "Acid  potassic  tartrate, 
tartar,  or  cremor  tartari,  C4H506K,  small  rhombic  crystals 
of  acid  taste,  sparingly  soluble  in  water,  is  much  used  in 
dyeing,  medicine,  &c.  Potassic  sodic  tartrate,  Rochelle  or 
seignette  salt,  C4H406KNa  +  4H20  (1672),  forms  magnificent 
rhombic  prisms.  Calcic  tartrate,  C4H406Ca  -f  4H90,  is  a 
powder  insoluble  in  water,  but  soluble  in  cold  caustic-soda 
solution;  on  warming  the  solution  it  separates  as  a  jelly, 
which  redissolves  upon  cooling.  Potassic  antimonyl-tartrate, 
tartar  emetic,  C4H406(SbO)'K  +  JH20  (see  B.  15,  1540),  is 
obtained  by  heating  cream  of  tartar  (cremor  tartari)  with  anti- 
mony oxide  and  water.  It  crystallizes  in  rhombic  efflorescent 
octahedra,  readily  soluble  in  water.  It  is  poisonous  and  acts 
as  an  emetic,  and  is  used  as  a  mordant  in  dyeing. 

Fehling's  solution  is  a  solution  of  cupric  sulphate  mixed  with 
alkali  and  Eochelle  salt,  and  is  largely  used  as  an  oxidizing 
agent.  Thus  with  various  carbon  compounds,  such  as  formal- 
dehyde, glucose,  fructose,  &c.,  it  readily  yields  a  precipitate  of 
cuprous  oxide. 

The  diethyl  ester  is  a  thick  oil,  while  the  monoethyl  ester 
crystallizes  in  prisms.  Aceto-tartaric  acid  and  amides  of 
tartaric  acid  are  known,  and  also  various  anhydrides.  As  an 
alcohol,  it  forms  with  nitric  acid  a  dinitric  ester,  the  so-called 
nitro-tartaric  acid,  C2H2(O  •  N02)2(C02H)2,  which  is  readily 
hydrolysed,  yielding  dihydroxy-tartaric  or  tartronic  acid. 

2.  Laevo-tartaric  acid  is  identical  in  its  chemical  and  also 
in  almost  all  its  physical  properties  with  ordinary  tartaric  acid, 
but  differs  from  it  in  that  its  solutions  turn  the  plane  of  polar- 
ization of  light  to  the  left,  in  a  degree  equal  to  that  in  which 
the  other  turns  it  to  the  right.     The  crystallized  salts  show 
hemihedral  faces   like  the  salts  of  dextro-tartaric  acid,  but 
oppositely  situated  (see  p.  254).     When  equal  quantities  of 
both  acids  are  mixed  together  in  aqueous  solution,  the  solu- 
tion becomes  warm,  and  we  obtain: 

3.  Eacemic    acid,    (C4H606)2,    2H20,   the    composition   of 
which  was  first  established  by  Berzelius,  who  recognized  it  as 
being  different  from  tartaric  acid,  and  who  developed  the  idea 
of  isomerism  from  this  first  example  in  1829.     Racemic  acid  is 
obtained  from  tartar  mother  liquor.     It  differs  from  dextro 
tartaric  acid  in  that  its  crystals  are  rhombic  and  efflorescent, 
and  also  less  soluble  in  water  than  the  former;  further,  the  free 
acid  is  capable  of  precipitating  a  solution  of  calcium  chloride 


254 


X     DIBASIC   ACIDS 


and  is  optically  inactive  (see  below).  The  salts,  which  are 
termed  racemates,  and  also  the  esters  (B.  21,  518),  show  small 
differences  from  the  tartrates  in  the  proportions  of  their  water 
of  crystallization,  in  solubility,  and  melting-point  or  boiling- 
point.  Molecular- weight  determinations  of  dilute  aqueous 
solutions  of  racemic  acid  indicate  that  under  these  conditions 
it  is  completely  resolved  into  d-  and  Z-tartaric  acids. 

4.  Meso-tartaric  acid,  a  fourth  tartaric  acid,  is  inactive  like 
the  foregoing,  but  non-resolvable  into  the  active  acids.  When 
heated  with  water  at  170°  it  is  partially  transformed  into 
racemic  acid,  which  can  then  be  resolved.  It  differs  from 
racemic  acid  and  also  from  the  active  acids  in  all  its  physical 
properties.  It  crystallizes  in  efflorescent  rectangular  plates, 
m.-pt.  143°.  The  acid-potassium  salt  is  readily  soluble  in  water. 

Racemic  Compounds.  Resolution  of  Racemic  Compounds  into 
their  Optically  Active  Components. — Racemic  acid  has  been  re- 
solved by  three  distinct  methods,  all  due  to  Pasteur;  and  as 
they  are  also  applicable  to  the  resolution  of  other  racemic 
compounds,  they  are  given  below. 

1.  When  a  solution  of  sodium-ammonium  racemate, 

Na(NH4)C4H406,  2H2O, 

is  evaporated,  beautiful  rhombic  crystals  having  the  compo- 
sition NaNH4C4H4O6,  4H20  and  showing  hemihedral  faces* 

*  Hemihedral  Faces. — These  are  small  faces  which  are  not  perfectly 
symmetrically  situated  with  respect  to  the  other  crystalline  faces;  they 
occur  in  only  half  the  positions  where  they  might  be  expected,  and  thus 
give  the  crystals  a  non-symmetric  structure. 

The  following  figs,  represent  crystals  of  the  d-  and  Z-sodic  ammonic 
tartrates : — 


The  faces  a  and  b  are  the  hemihedral  faces,  and  it  will  be  noticed  that 
the  two  crystals  are  non-superposable,  but  stand  in  the  relationship  of 
object  to  mirror-image. 


RESOLUTION   OF  RACEMIC   COMPOUNDS  255 

are  obtained.  Pasteur  observed  that  these  faces  were  not 
always  similarly  situated,  but  that  certain  crystals  were 
dextro-hemihedral,  while  others  were  Isevo-hemihedral,  so 
that  one  crystal  formed  the  reflected  image  of  the  other. 
The  Isevo-hemihedral  crystals  when  dissolved  exhibit  dextro- 
rotation,  and  vice  versa.  If  now  the  two  kinds  of  crystals  be 
separated  from  one  another  mechanically,  and  the  free  acid 
liberated  from  each,  this  will  be  found  to  consist,  not  of  racemic 
acid,  but  in  the  one  case  of  dextro-  and  in  the  other  of  Isevo- 
tartaric  acid. 

In  the  process  of  crystallization  it  is  essential  that  the  tem- 
perature should  be  below  27°,  as  otherwise,  in  place  of  the 
enantiomorphously  related  crystals  of  sodic-ammonic  d-  and 
/-tartrates,  it  is  found  that  the  crystals  are  all  alike,  possess 
no  hemihedral  faces,  and  consist  of  sodic-ammonic  racemate. 
This  temperature  is  termed  the  transition  point,  and  for  each 
racemic  compound  there  is  a  definite  transition  temperature. 
Thus  for  sodic-potassic  racemate  it  is  3°,  for  rubidic  racemate 
40 '4°,  for  ammonic-hydric  malate  74°. 

In  the  case  of  sodic-ammonic  racemate  the  transition  tem- 
perature may  be  determined  by  means  of  a  dilatometer  (Varit 
Hoff  and  Deventer,  Zeit.  Phys.,  1887,  1,  173).  This  is  a  large 
thermometer,  the  bulb  of  which  is  filled  with  an  equimolecular 
mixture  of  the  two  active  salts  and  covered  with  oil,  the  level 
of  which  can  be  read  off  on  the  stem.  As  the  temperature  of 
the  dilatometer  is  raised  gradually,  a  considerable  increase  in 
volume  is  noticed  at  27°,  due  to  the  change  expressed  by  the 
equation : 

NaNH4C4H406,  4H2O  +  NaNH4C4H406, 4H2O 

=  (NaNH4C4H406)2,  2H2O  +  6H2O. 

Other  racemic  compounds  have  been  resolved  by  this  simple 
method  of  crystallization.  In  all  cases  the  temperature  em- 
ployed must  be  below  the  transition  temperature  of  the  given 
substance,  i.e.  below  the  temperature  at  which  the  mixture 
of  active  components  becomes  transformed  into  the  racemic 
compound.  In  this  method  of  resolution  no  differences  in 
solubility  of  the  two  components  are  met  with,  and  hence  no 
process  of  fractional  crystallization  can  be  employed;  the  two 
salts  are  deposited  side  by  side,  and  must  be  picked  out  indi- 
vidually. The  resolution  of  zinc  ammonic  lactate  has  already 
been  mentioned  (p.  215);  further  examples  are  sodic-potassic 
racemate,  asparagin,  and  camphoric  acid. 


256  X.    DIBASIC   ACIDS 

2.  A  very  common  method  of  resolving  racemic  acids  is  by 
combination  with  an  optically  active  base,  e.g.  an  alkaloid.     In 
the  case  of  racemic  acid  itself,  Pasteur  used  /-cinchonine.     The 
two  salts  formed  are  (a)  d-acid  -f-  /-base,  (b)  /-acid  +  /-base. 
As  these  two  salts   are   not  enantiomorphously  related,  i.e. 
their  molecules  do  not  stand  in  the  relationship  of  object  to 
mirror-image,  they  possess  different  solubilities,  and  may  be 
separated  by  fractional  crystallization. 

The  following  is  a  list  of  some  simple  racemic  compounds 
which  have  been  resolved  by  this  method;  the  salt  named  is 
the  less  soluble  of  the  two,  and  crystallizes  first. 

Acids. — Quinine:  d-tartrate.  Strychnine:  /-lactate,  d-methyl- 
succinate,  ^-methoxy-succinate,  c/-phenyldibromo-propionate. 
Cinchonine:  /-tartrate,  d^-malate,  d-mandelate.  Brucine:  d-tar- 
trate,  /-valerate,  /-aspartate. 

Racemic  bases  may  be  resolved  by  a  similar  process,  viz. 
by  combination  with  an  optically  active  acid,  e.g.  d-tartaric,  or 
even  better,  d-bromocamphor-sulphonic  acid,  and  separating 
the  two  salts  thus  obtained  by  fractional  crystallization.  Thus 
ethyl-piperidine  and  coniine  have  been  resolved  by  Ladenburg 
by  using  d-tartaric  acid  (A.  1888,  247,  85;  cf.  also  Pope  and 
Harvey  on  resolution  of  tetrahydro-/3-naphthylamine,  J.  C.  S. 
1901,  74;  also  Pope  and  Peachey,  ibid.  1899,  1066  and  1105). 

3.  The  third  method  consists  in  subjecting  a  solution  of  an 
ammonium  salt  of  the  acid  to  the  action  of  some  of  the  lower 
plant  organisms,  e.g.  moulds,  bacteria,  yeasts,  &c.     Different 
organisms  are  required  in  different  cases.     Pasteur  found  that 
ordinary  green  mould — Penicillium  glaucum — when  grown  in  a 
solution  of  ammonium  racemate,  destroys  the  salt  of  the  c?-acid 
and  leaves  a  solution  of  the  salt  of  the  ^acid.     If,  however,  the 
decomposition  is  allowed  to  proceed,  the  /-salt  is  also  destroyed ; 
the  reaction  is  a  preferential  decomposition,  and,  if  stopped  at 
a  suitable  time,  practically  all  d-salt  will  have  disappeared.     It 
is  obvious  that  in  this  method  one  of  the  active  components  is 
lost;  but  by  using  two  distinct  organisms  in  separate  solutions 
it  is  sometimes  possible  to  obtain  both  d-  and  /-compounds. 
Thus  Penicillium  glaucum  grown  in  a  solution  of  a  salt  of  d-l- 
mandelic  acid  leaves  the  d-salt,  and  Saccharomyces  ellipsoideus 
leaves  the  /-salt. 

Among  other  resolutions  which  have  been  effected  by  this 
method  may  be  mentioned  the  destruction  of  /-lactic,  /-mandelic, 
d-glyceric,  /-ethoxy-succinic  acids,  and  of  d-methylpropyl-car- 
binol  by  Penicillium  glaucum,  and  the  destruction  of  d-mandelic, 


RACEMIG   COMPOUNDS  257 

?-phenyldibromo-propionic  acids  and  of  ^-glucose,  d-fmctose, 
and  ^-manno.se  by  yeast  (different  species). 

4.  Markwald  and  M'Kenzie  (B.  1901,  34,  469)  have  suggested 
another  method  of  resolution,  viz.  by  esterifying  the  racemic 
acid  with  an  optically  active  alcohol.     They  used  r-mandelic 
acid  and  Z-menthol,  and  found  that  the  ^-component  of  the 
racemic  acid  was  esterified  somewhat  more  rapidly  than  the  /. 
(Of.  also  Mackenzie,  J.  C.  S.  1904,  378.) 

5.  Ostromisslensky  (B.  1908,  41,  3035)  has  shown  that  a  mix- 
ture of  d-  and  /-isomerides  can  be  easily  separated  if  a  super- 
saturated solution  of  the  mixture  is  impregnated  with  a  crystal 
of  a  suitable  active  material,  thus  a  crystal  of  /-asparagine 
(p.  248)  immediately  produces  the  deposition  of  d-sodium  am- 
monium tartrate  from  a  supersaturated  solution  containing  the 
d-  and  /-salts.     A  crystal  of  any  optically  active  tartrate  or  of 
any  isomorphous  substance  will  also  cause  a  separation  of  one 
of  the  active  sodium  ammonium  tartrates,  the  actual  salt  de- 
posited depending  on  the  activity  of  the  crystal  used,  e.g. 
c?-sodium  tartrate  always  deposits  c?-sodium  ammonium  tar- 
trate.    It  is  not  necessary  that  the  impregnating  substance 
should  be  optically  active;  it  must,  however,  be  isomorphous 
or  isodimorphous.     Thus  a  crystal  of  glycine  can  cause  the 
deposition  of  Z-asparagine  from  a  supersaturated  solution  of 
d-l  asparagine. 

This  method  of  resolution  cannot  be  used  when  the  super- 
saturated solution  contains  a  definite  racemic  compound  of  the 
d-l  isomerides,  and  can  thus  be  used  as  a  method  for  deter- 
mining whether  the  given  substance  exists  in  solution  as  a 
d-l  conglomerate  or  as  a  true  racemic  compound. 

Racemisation. — When  d-tartaric  acid  is  heated  with  a  small 
amount  of  water  at  175°  racemic  acid  is  formed,  together  with 
a  small  amount  of  the  meso  acid.  This  conversion  of  an 
optically  active  compound  into  its  racemic  isomeride  is  usually 
termed  racemisation,  and  is  to  be  attributed  to  the  transforma- 
tion of  50  per  cent  of  the  original  active  acid  into  its  optical 
isomer.  As  further  examples  of  racemisation,  may  be  men- 
tioned the  heating  of  d- valeric  acid  with  concentrated  sul- 
phuric acid  and  of  amyl  alcohol  with  sodium  hydroxide. 
When  valeric  acid  is  boiled  for  eighty  hours  partial  racemi- 
sation occurs,  as  is  indicated  by  a  slight  diminution  in  its 
rotatory  power.  Racemisation  often  occurs  during  a  chemical 
reaction;  thus  Z-mandelic  acid,  C6H5-CH(OH).C02H,  and 
hydrobromic  acid  at  50°  yield  not  /-phenylbromo-acetic  but 

(B480)  $ 


258 


X.    DIBASIC   ACIDS 


r-phenylbromo-acetic  acid.  (Cf.  also  Easterfield,  J.  C.  S.  1891, 
72;  Pope,  ibid.  1901,  81,  and  P.  1900,  116.) 

Occasionally  the  racemisation  occurs  at  the  ordinary  tem- 
perature, and  is  then  termed  autoracemisation;  thus  d-phenyl- 
bromo-acetic  acid  when  kept  in  benzene  solution  for  some 
three  years  becomes  quite  inactive,  and  ethyl  d-bromo-suc- 
cinate  in  the  course  of  four  years  diminishes  in  rotatory  power 
from  +40-96°  to  +9°  (Walden,  B.  1898,  31,  1416). 

Criteria  for  Determining  the  Nature  of  the  Racemic  Compound. 
—The  racemic  substance  may  be  one  of  the  following: — (a)  A 
definite  compound  of  1  molecule  of  the  ^-component  with  1  of 
the  I.  (b)  An  ordinary  mixture  of  the  two  in  molecular  pro- 
portions, (c)  Mixed  crystals,  i.e.  a  solid  solution  of  the  two 
isomorphous  antipodes  without  chemical  combination.  The 
first  are  termed  racemic  compounds  proper,  the  second  inactive 
conglomerates,  and  the  third  pseudoracemic  compounds  (Kip- 
ping and  Pope,  J.  C.  S.  1897,  989). 

A  true  racemic  compound  cannot  be  recognized  by  mole- 
cular-weight determinations,  as  in  the  gaseous  form  or  in 
solution  it  is  usually  resolved  into  its  components.  In  certain 
cases  the  recognition  of  the  substance  as  a  racemic  compound 
is  simple,  e.g.  sodic-ammonic  racemate,  which  crystallizes  in 
a  different  crystallographic  system,  and  contains  a  different 
amount  of  water  of  crystallization  from  the  active  isomers, 
and  possesses  a  definite  transition  point. 

When  such  simple  criteria  are  of  no  use,  Backhuis  Eoozeboom 
(Zeit.  Phys.  1899,  28,  494)  recommends  a  study  of  the 
melting-point  curves.  These  are  obtained  by  taking  the 
melting-points  of  mixtures  of  the  compounds  in  different 
proportions,  and  then  plotting  the  melting-points  against 
the  composition.  The  following  types  of  curves  are  met 
with: — 

Conglomerates,  fig.  1.  Racemic  compounds,  figs.  2  and  3. 
Mixed  crystals,  figs.  4,  5,  and  6. 


B 


POLYHYDROXY  DIBASIC  ACIDS 
C 


B 


B 


259 


A  represents  the  melting-point  of  the  pure  ^-compound,  B  that 
of  the  pure  I,  and  C  that  of  the  racemic  compound  or  mixture. 
These  curves  should  be  studied  by  aid  of  the  Phase  rule. 

E.  Polyhydroxy  Dibasic  Acids 

Trihydroxy  -  glutaric  acid,  C02H  •  CH(OH)  •  CH(OH)  • 
CH(OH)  •  C02H,  and  the  stereo -isomeric  acids — saccharic, 
mucic,  and  isosaccharic  acid— C02H  •  CH(OH)  •  CH(OH)  • 
CH(OH).CH(OH).C02H,  are  the  best-known  examples. 

Many  of  these  acids  form  lactones  (p.  217),  the  so-called 
lactonic  acids,  and  some  of  them  also  double  lactones  (cf.  Fittig, 
A.  255,  1,  et  seq.). 

Trihydroxy-glutaric  acid,  C02H.(CH.OH)3.C02H,  is  a  fre- 
quent oxidation-product  of  sugar  varieties,  e.g.  of  xylose  and 
arabinose.  According  to  theory,  four  stereo-isomers  should 
exist,  and  four  are  actually  known;  they  may  be  represented 
by  the  following  projection  formulae,  where  X  =  C02H: — 


^\. 


OH4-H 
H-j-OH 
H-j-OH 

X 


H-^OH 
HO4-H 
HO-j-H 

X 


H-OH 
H-hOH 


HOHE 
H-K)H 

X 


Nos.  1  and  2  are  enantiomorphously  related  and  optically 
active,  and  can  form  a  racemic  compound.  Compounds  3  and 
4  are  inactive  substances  of  the  type  of  mesotartaric  acid. 

Saccharic  acid  is  produced  by  the  oxidation  of  cane-sugar, 
glucose,  gulose,  gulonic  acid,  mannitol,  or  starch  by  nitric 
acid,  and  exists  in  the  d-,  Z-,  and  r-forms  (see  Glucoses);  (/-sac- 
charic acid  when  reduced  yields  glycuronic  acid  (see  p.  222). 
All  the  three  varieties  are  deliquescent. 

Mucic  acid  is  formed  by  oxidizing  dulcitol,  the  gums,  muci- 


260  X.   DIBASIC  ACIDS 

lages,  and  milk-sugar.  It  is  a  sparingly  soluble,  colourless, 
crystalline  powder.  The  molecule  being  symmetrical  in  struc- 
ture, it  is  optically  inactive.  It  is  easily  converted  into  deri- 
vatives of  furane  (see  this). 

Isosaccharic  acid  is  obtained  by  the  oxidation  of  glucos- 
amine,  C6Hn06(NH2). 

Theoretically,  ten  stereo -isomeric  acids  of  the  formula 
C02H-[CH.OH]4.CO2H  are  possible,  most  of  which  (e.g.  el- 
and i-manno-saccharic  acids,  talomucic  acid,  &c.)  have  been 
prepared  by  E.  Fischer  (B.  24,  539,  2137,  3622).  For  their 
relations  to  the  hexoses,  see  the  table  appended  to  these. 

F.  Dibasic  Ketonic  Acids 

Dibasic  ketonic  acids  unite  in  themselves  the  properties  of  a 
ketone  and  of  a  dibasic  acid.  The  following  are  known : — 

1.  Mesoxalic  acid,  CO(C02H)2  or  C(OH)2(C02H)2  (see  p. 
199),  is  prepared  from  dibromo-malonic  acid,  CBr2(C02H)2, 
and  baryta  water  or  oxide  of  silver,  thus: — 

CBr2(C02H)2  +  H20  =  CO(CO2H)2  +  2HBr; 

also  by  boiling  alloxan  (p.  288)  with  baryta  water.  It  crys- 
tallizes in  deliquescent  prisms  (-f  ILO). 

As  a  ketone  it  combines  with  NaHS03,  reacts  with  hy- 
droxylamine,  and  is  reduced  by  nascent  hydrogen  to  tar- 
tronic  acid: 

O)2H.CO.CO2H  +  2H  =  CO2H.CH(OH).CO2H. 

Since  the  acid  and  its  salts  still  retain  a  molecule  of  water 
at  temperatures  above  100°,  this  may  be  united  in  much  the 
same  manner  as  the  water  in  chloral  hydrate,  corresponding 
with  the  formula  C(OH)2(C02H)2,  "  dihydroxy-malonic  acid  ". 
In  fact,  two  modifications  of  the  ethyl  ester  are  known,  viz. 
C(OH)2(C02C2H5)2  and  CO(C02C2H5)2. 

2.  Oxal-acetic  acid,  Butanone  diacid,  C02H  •  CH2  •  CO  •  C02H, 
is  an  acid  corresponding  in  many  respects  with  aceto-acetic  acid. 
Its  ethyl  ester  is  prepared  by  the  action  of  sodium  ethoxide 
upon  a  mixture  of  ethyl  oxalate  and  acetate  (p.  224),  and 
also  by  the  action  of  concentrated  sulphuric  acid  upon  ethyl 
acetylene-dicarboxylate.     It  is  a  colourless  oil,  but  the  alco- 
holic solution  gives  an  intense  dark-red  coloration  with  ferric 
chloride.     It  is  of  importance  as  a  synthetical  reagent,  as  the 
hydrogen  atoms  of  the  methylene  group  can  be  replaced  by 


POLYBASIC   ACIDS  261 

Sodium,  and  hence  by  various  alkyl  and  acyl  radicals  (W. 
fPislicenus). 

3.  Acetone -dicarboxylic  acid,  Pentanone  diatid,  CO(CH2« 
C02H)2,  obtained  by  treating  citric  acid  with  concentrated 
H2S04,  readily  decomposes  into  acetone  and  2C02  (see  A.  261, 
151). 

4.  Dihydroxy-tartaric  acid,  C02H .  CO  -  CO  •  C02H,  or  pro- 
bably  C02H.C(OH)2.C(OH)2.C02H,    is   formed   from  pyro- 
catechol  and  nitrous  acid,  and  by  the  gradual  decomposition 
of  nitro-tartaric  acid.      It  melts  at  98°.      The  characteristic 
sparingly  soluble  sodium  salt  decomposes  readily  into  carbon 
dioxide  and  sodium  tartronate. 

CH8.CO.CH.CO,H 

5.  Diaceto-succmic  acid,  ^^^^^  (see  p.  229). 

The  ester  of  this  is  closely  related  to  acetonyl-acetone,  the 
latter  being  readily  obtainable  from  the  former  by  the  action 
of  caustic-soda  solution  ("Ketonic  decomposition":  cf.  B.  33, 
1219). 

6.  Diacetoglutaric  acid,  (X)2H .  CHAc  •  CH2  •  CHAc  •  COSH. 
The  ester  of  this  acid  is  formed  by  condensing  ethyl  aceto- 
acetate  with  formaldehyde  in  the  presence  of  diethyl  amine, 
and  is  readily  converted  into  derivatives  of  tetrahydrobenzenf 
or  pyridine  (Knoewnagel,  A.  281,  94;  cf.  also  B.  31,  1388). 

Most  of  these  ketonic  acids  exhibit  keto-enolic  tantomerism, 
thus  5  isomerodes  of  diacetyl-succinic  acid  are  known  (Knorr, 
A.  1899,  306,  332). 

XL   POLYBASIC  ACIDS 

The  polybasic  acids  contain  two  or  more  carboxylic  groups 
in  the  molecule.  The  tribasic  acids,  like  phosphoric  acid,  can 
give  rise  to  three  series  of  salts — normal,  monoacid,  and  di- 
acid.  Both  saturated  and  unsaturated  acids  are  known,  and 
also  substituted  derivatives. 

A.  Saturated  and  Unsaturated  Polybasic  Acids 

A  simple  tribasic  acid  is  tricarballylic  acid,  symmetrical  pro- 
pane-tricarboxylic  acid,  C02H.CH2.CH(C02H).CH2.C02H. 
It  occurs  in  unripe  beet,  and  is  prepared  (a)  by  the  addition 
of  hydrogen  to  aconitic  acid,  (b)  by  heating  citric  acid  with 
hydriodic  acid,  and  (c)  synthetically  from  glycerol  by  trans- 
forming it  into  the  tribromhydrin,  C8H6Br8,  treating  this  with 


262  XL   POLYBASIC  ACH>S 

KCN,  and  hydrolysing  the  cyanide  formed,  C3H5(CN)3.  Since 
the  three  hydroxyls  in  glycerol  are  distributed  among  three 
carbon  atoms,  the  same  holds  good  for  the  carboxyls  in  the 
acid,  which  has,  therefore,  the  symmetrical  constitution: 

C02H  •  CH2  •  CH(C02H) .  CH2 .  CO2H. 

This  acid  is  of  importance  in  determining  the  constitution 
of  citric  acid,  from  which,  as  already  seen,  it  can  be-  obtained 
by  reduction  with  HI.  It  crystallizes  in  rhombic  prisms,  is 
readily  soluble  in  water,  and  melts  at  166°. 

An  unsaturated  tribasic  acid  closely  related  to  tricarballylic 
acid  is  aconitic  acid,  C02H.CH:C(C02H).CH2.C02H,  which 
contains  two  atoms  of  hydrogen  less  than  tricarballylic  acid. 
It  is  found  in  nature,  in  Aconitum  Napellus,  shave-grass,  sugar- 
cane, beet-root,  &c.,  and  is  prepared  by  heating  citric  acid, 
C6H807,  when  the  elements  of  water  are  eliminated.  It  is  a 
strong  acid,  crystallizable,  readily  soluble  in  water,  melts  at 
191°,  and  is  reduced  by  nascent  hydrogen  to  tricarballylic 
acid,  hence  its  constitution. 

B.  Hydroxy  Polybasic  Acids 

Citric  acid,  acidum  citricum,  hydroxy-tricarballylic  acid,  C02H  • 
CH2.C(OH)(C02H).CH2.CO2H  (Sdieele,  1784;  recognized  as 
tribasic  by  Liebig  in  1838),  occurs  in  the  free  state  in  lemons, 
oranges,  and  red  bilberries,  and  mixed  with  malic  acid  in 
gooseberries,  &c.,  also  as  calcium  salt  in  woad,  potatoes,  beet- 
root, &c.  It  is  usually  prepared  from  the  juice  of  lemons  by 
means  of  the  lime  salt.  It  crystallizes  in  large  rhombic  prisms 
(  +  H20),  is  readily  soluble  in  water,  moderately  in  alcohol, 
but  only  sparingly  in  ether.  It  loses  its  water  of  crystal- 
lization at  130°,  melts  at  153°,  and  breaks  up  at  a  higher 
temperature  first  into  aconitic  acid  and  water,  and  then  into 
carbon  dioxide,  itaconic  acid,  citraconic  anhydride,  and  acetone. 
Oxidizing  agents  effect  a  verv  thorough  decomposition. 

Calcium  citrate  is  precipitated  as  a  white  sandy  powder 
when  a  mixture  of  calcium  chloride  and  alkali  citrate  solutions 
is  boiled.  The  three  series  of  salts  are  well  characterized;  the 
alkali  salts  are  soluble  in  water,  the  others  mostly  insoluble. 
Among  the  derivatives  may  be  mentioned  mono-,  di-,  and'  tri 
ethyl  citrates  and  triethyl  aceto-citrate, 

CO2Et  •  GH,  •  0(0  -  CO  •  CHaXCOgEt)  •  CHS .  COaEt. 


CYANOGEN  COMPOUNDS  263 

The  formation  of  this  last  is  a  direct  proof  of  the  alcoholic 
character  of  citric  acid.  The  amides  of  citric  acid  are  con- 
verted by  concentrated  H2S04  into  citrazinic  acid,  C6H5N04, 
a  pyridihe  derivative  (B.  17,  2681). 

The  constitution  of  citric  acid  is  arrived  at  (a)  from  its  con- 
version into  aconitic  acid  by  the  elimination  of  water,  (b)  from 
its  reduction  to  tricarballylic  acid,  and  (c)  from  its  synthesis 
from  1  :  3  dichloroacetone,  e.g.  : 


CH2C1.CO.CH2C1  +  HCN  —  CH2C1.C(OH)(CN).CH2C1 

—  CN.CH2.C(OH)(CN).CH2.CN 
—  CX)2H.CH2.C(OH)(C02H).CH2.C02H. 

The  acid  has  been  synthesised  by  Lawrence  (J.  C.  S.  1897, 
71,  457)  by  an  application  of  Eeformatsky's  reaction,  i.e.  the 
condensation  of  a  halogen  derivative  with  a  ketone  in  the 
presence  of  zinc.  The  substances  used  were  ethyl  bromacetate, 
ethyl  oxalacetate,  and  pure  zinc  turnings  : 


_  CO2Et-CH2.C(OZnBr).CO2Et 
CH2.CO2Et. 

This  condensation  product  reacts  with  water,  yielding  ethyl 
citrate,  C02Et.CH2.C(OH)(C02Et).CH2.C02Et,  zinc  oxide, 
and  hydrogen  bromide. 

Citric  acid  is  also  formed  when  solutions  of  glucose  are  fer- 
mented by  certain  moulds,  e.g.  Citromycetes  pfefferianus  and 
C.  glaber  (Wehner,  Bull.  Soc.  Chim.  1893  [III],  9,  728). 

Acids  containing  more  than  three  carboxylic  groups  do  not, 
as  a  rule,  occur  in  nature,^  but  a  number  of  esters  of  such  acids 
have  been  prepared  by  means  of  the  aceto-acetic  ester  and 
malonic  ester  syntheses. 


XII.   CYANOGEN  COMPOUNDS 

Under  the  name  of  the  cyanogen  compounds  is  included  a 
group  of  substances  which  are  derivable  from  cyanogen,  C2N2. 
Cyanogen  itself  is  a  gas  of  excessively  poisonous  properties 
which  behaves  in  many  respects  like  a  halogen;  and  its 
hydrogen  compound,  hydrocyanic  acid,  HCN,  is  an  acid  re- 


264  XII.    CYANOGEN   COMPOUNDS 

sembhng  hydrochloric  acid  to  a  certain  extent.  In  many 
cyanogen  compounds  the  monovalent  group  (CN)  plays  the 
part  of  an  element;  cyanogen  is  to  be  regarded  as  the  isolated 
radical  (CN),  which,  however,  possesses  the  double  formula 
C2N2,  just  as  a  molecule  of  chlorine  (C12)  is  made  up  of  two 
atoms.  The  cyanogen  group  is  further  capable  of  combining 
with  the  halogens,  hydroxyl,  sulphydril  (SH),  amidogen,  &c. 
From  the  compounds  so  obtained  numerous  others  are  derived 
by  the  entrance  of  alkyl  radicals  in  place  of  hydrogen.  Such 
derivatives  invariably  exist  in  two  isomeric  forms,  sharply 
distinguished  from  one  another  by  their  properties.  They 
are  often  termed  normal  and  iso  compounds,  and  the  isomerism 
is  of  very  great  interest.  (See  table,  p.  265.) 

Polymeric  modifications  of  most  of  those  compounds  also 
exist.  The  number  of  cyanogen  compounds  known  is  thus  a 
very  large  one. 

Carbon  and  nitrogen  do  not  combine  directly  except  in  the 
presence  of  an  alkali,  and  then  a  metallic  cyanide  is  formed. 
As  examples  of  this  reaction,  we  have  the  following:— 

1.  When  nitrogen  is  led  over  a  red-hot  mixture  of  coal  and 
carbonate  of  potash,  potassium  cyanide,  KCN,  is  formed,  espe- 
cially under  a  high  pressure. 

2.  Ammonium  cyanide  is  formed  when  ammonia  is  passed 
over  red-hot  coal. 

3.  Potassium  cyanide  is  formed  when  nitrogenous  organic 
compounds  such  as  leather,  horn,  claws,  wool,  blood,  &c.,  are 
heated  with  potashes. 

4.  Hydrocyanic  acid   is  formed  when  electric  sparks   are 
passed  through  a  mixture  of  acetylene  and  nitrogen,  and  also 
by  the  action  of  the  silent  electric  discharge  on  a  mixture 
of  cyanogen  and  hydrogen.     It  is  also  formed  (commercial 
method)  when  a  carefully  dried  mixture  of   hydrogen,  am- 
monia, and  a  volatile  carbon  compound  (CO,  C02,  C2H2,  &c.) 
is  passed  over  heated  platinized  pumice.     (For  further  modes 
of  formation,  see  p.  266  et  seq.) 

The  original  material  for  the  preparation  of  most  of  the 
cyanogen  compounds  is  potassium  ferrocyahide,  which  is  manu- 
factured on  the  large  scale  and  possesses  the  great  advantage 
over  potassium  cyanide  of  being  stable  in  the  air  and  compara- 
tively non-poisonous. 


I 

CYANOGEN  COMPOUNDS 
SUMMARY  OF  THE  CYANOGEN  COMPOUNDS 


Relation  to  carbonic  acid,  &c. 
(&ee  p.  279.) 

Name. 

Formula. 

Nitrile  of  oxalic  acid, 

Cyanogen, 

N:C-C:N 

Nitrile  of  formic  acid, 

Hydrocyanic  acid, 
Alkyl  derivatives: 
(a)  Nitriles, 
(6)  Isonitriles, 

NiC.H 

R.CiN 
R-N:C 

Cyanogen     chloride, 
bromide,  iodide, 

N-C-Cl 

CO3H2  +  NH3-2H2O, 

(Nitrile  of  carbonic  acid, 
eventually  Carbiinide), 

Cyanic  acid, 
Alkyl  derivatives: 
(a)  Methyl  cyanate, 
(6)      „    isocyanate, 

N-C-OH 

N:C-O.CH3 
O:C:N.CH3 

Thiocyanic  acid, 
Alkyl  derivatives  : 
(a)  Ethyl  thiocyanate 
(6)  Allyl    isothio- 
cyanate, 

N-C-SH 

N:C.S.C2H5 
S:C:NC3H6 

CO3H2  -f  2NH3  —  3H2O, 
(Nitrile  and  amide  of  car- 
bonic acid,  eventually 
Carbo-di-imide,  see  p. 
277), 

Cyanamide, 
Alkyl  derivatives: 
(a)  Alkyl  cyana- 
mide, 
(6)  Carbo-di-imide, 

N:C-NH2 

NiC-NH-K 
RN:C:NK* 

The   amic   acid   of    car- 
bonic acid, 

Carbamic  acid, 

NH2.CO-OH 

The  amide  of  carbonic 
acid, 

Urea, 

CO(NH2)2 

Thio-urea, 
Alkyl  derivatives  : 
(a)  Alkyl-thio-ureas, 
(6)  Imido-thio-carba- 
mine  compounds, 

CS(NH2)2 

NH2.CS.NHR 
NH:<™2 

CO3H2  +  3NH3-3H2O, 
(Amidine), 

Guanidine, 

HNlCKNHj)., 

*  R  =  alkvl  radical. 


266  XII.   CYANOGEN  COMPOUNDS 

A.  Cyanogen  and  Hydrocyanic  Acid 

Cyanogen,  N-C-CjN,  which  was  discovered  by  Gay-Lussac 
in  1815,  occurs  in  the  gases  of  blast-furnaces  and  in  coal  gas. 

As  the  nitrile  of  oxalic  acid,  it  may  be  obtained  by  the 
abstraction  of  the  elements  of  water  from  ammonium  oxalate 
by  means  of  P4010;  also  in  the  same  way  from  the  intermediate 
product  of  this  reaction,  oxamide : 

NH40-CO.CO.ONH4-4H9O  =  N:C-C:N, 
NH2.CO.CO.NH2       -2H20  =  N:C-C:N. 

It  is  usually  prepared  by  heating  dry  silver  cyanide,  AgCN, 
or  mercuric  cyanide,  Hg(CN)2,  strongly : 

Hg(CN)2  =  Hg  +  C2N2; 

or  by  heating  a  solution  of  cupric  sulphate  with  potassium 
cyanide  (B.  18,  Kef.  321). 

Cyanogen  is  a  colourless  gas  of  a  peculiar  unpleasant  odour 
resembling  that  of  bitter  almonds,  and  is  terribly  poisonous. 
It  is  easily  liquefied  and  solidified  (sp.  gr.  1*8  of  the  liquid; 
m.-pt.  —34°;  b.-pt.  —21°),  is  soluble  in  0'25  vol.  of  water  and 
in  even  less  alcohol.  The  solutions  become  dark  upon  stand- 
ing, with  separation  of  a  brown  powder  ("Azulmic  acid"), 
while  oxalic  acid,  ammonia,  formic  acid,  hydrocyanic  acid,  and 
urea  are  to  be  found  in  the  liquid.  The  formation  of  the 
oxalic  acid  and  ammonia  is  due  to  normal  hydrolysis,  and  that 
of  formic  acid  to  the  hydrolysis  of  the  hydrocyanic  acid  formed 
as  an  intermediate  product.  In  presence  of  a  minute  quantity 
of  aldehyde,  oxamide  is  formed  as  the  result  of  the  addition  of 
water.  Cyanogen  combines  with  heated  potassium  to  KCN, 
and  dissolves  in  aqueous  potash  to  form  KCN  and  KCNO. 

Paracyanogen,  (CN)X,  is  a  polymer  of  cyanogen.  It  is  an 
amorphous  brown  powder  which  is  formed  as  a  by-product 
when  mercuric  cyanide  is  heated;  upon  further  heating,  it  is 
transformed  into  cyanogen. 

Hydrocyanic  acid,  pmssic  acid,  CNH,  was  discovered  about 
the  year  1782  by  Scheele,  and  investigated  closely  by  Gay- 
Lussac. 

Some  of  the  more  interesting  methods  of  formation  are  the 
following : — 

1.  It  is  readily  liberated  from  its  salts  by  the  action  of 
almost  any  other  acid,  even  carbonic  acid;  and  even  complex 


HYDROCYANIC  ACID  267 

cyanides,   e.g.   potassium    ferrocyanide,    when   distilled    with 
moderately  dilute  sulphuric  acid  yield  hydrogen  cyanide: 


K4Fe(CN)6  +  5H2S04  =  6HCN  +  FeSO4  +  4KHSO4. 

The  ferrous  sulphate  produced  reacts  with  more  ferrocyanide 
to  form  potassium  ferrous  ferrocyanide,  FeK2(FeC6N6),  which  is 
not  affected  by  dilute  acids  (see  p.  269);  consequently  only  half 
of  the  cyanogen  present  is  converted  into  hydrocyanic  acid. 
When  concentrated  sulphuric  acid  is  employed  in  place  of  the 
dilute,  carbon  monoxide  and  not  hydrocyanic  acid  is  obtained. 

2.  As  the  nitrile  of  formic  acid,  it  may  be  prepared  by  the 
action  of  dehydrating  agents  on  ammonium  formate  or  form- 
amide  : 

H.CO-ONH4  =  H.CO.NH2  +  H2O  =  HGN  +  2H2O. 

3.  Together  with  oil  of  bitter  almonds,  C6H5.CHO,  and 
grape-sugar,    C6H1206,    by   the   hydrolysis   of    the    glucoside 
amygdalin  under  the  influence  of  the  enzyme  "  emulsin  "  (see 
Benzaldehyde)  : 

SH0  = 


The  oil  of  bitter  almonds  and  its  aqueous  solution  (aqua 
amarum  amygdalarum)  —  prepared  from  the  almonds  them- 
selves —  consequently  contain  HCN. 

The  acid  occurs  in  the  free  state  in  the  tree  Pangium  edule, 
found  in  Java,  more  particularly  in  the  seeds.  It  exists  in 
the  form  of  glucosides  in  various  plants  (C.  C.  1906,  ii,  1849: 
1909,  i,  387). 

4.  By  the  action  of  ammonia  and  chloroform  on  alcoholic 
potash  under  pressure.  Cf.  p.  103. 

For  other  syntheses,  see  p.  264. 

Hydrogen  cyanide  is  a  colourless  liquid  boiling  at  25° 
and  solidifying  at  —12°.  Sp.  gr.  0'70.  It  has  a  peculiar 
odour  and  produces  an  unpleasant  irritation  in  the  throat,  is 
miscible  with  water,  and  burns  with  a  violet  flame.  Like 
potassium  cyanide,  it  is  one  of  the  most  terrible  of  poisons. 
The  best  antidotes  are  stated  to  be  hydrogen  peroxide  or 
small  quantities  of  chlorine  mixed  with  air.  When  absolutely 
pure  it  can  be  preserved  unchanged,  but  it  decomposes  in 
presence  of  traces  of  water  or  ammonia,  with  separation  of 
a  brown  mass  and  formation  of  ammonia,  formic  acid,  oxalic 
acid,  &c.  The  addition  of  minute  quantities  of  mineral  acids 
renders  the  aqueous  solution  more  stable. 


268  XII.    CYANOGEN   COMPOUNDS 

Liquid  hydrocyanic  acid  is  a  good  solvent  for  many  salts, 
and  has  a  high  ionizing  power.  Acids  (sulphuric  and  trichloro- 
acetic),  however,  do  not  appear  to  dissociate  when  dissolved 
in  the  liquid. 

The  acid  has  many  properties  of  an  unsaturated  compound. 
It  is  readily  reduced  by  nascent  hydrogen  to  methylamine. 
In  the  presence  of  hydrochloric  acid  it  combines  with  water 
yielding  formamide.  With  diazomethane  (Chap.  LI)  it  yields 
methyl  cyanide  together  with  methyl  carbylamine.  With 
hydrogen  chloride  it  gives  iminoformyl  chloride,  NHrCHCl,  a 
compound  of  importance  in  the  synthesis  of  aromatic  alde- 
hydes (A.  1906,  347,  347);  but  has  not  been  isolated.  From 
ethyl  acetate  solution  a  product  2HCN,  3HC1  =  NH:CH-NH- 
CHC12,  HC1,  dichloromethyl  formamidine  hydrochloride  is 
obtained.  It  combines  directly  with  most  aldehydes  and 
ketones,  yielding  cyanhydrins  (nitriles  of  hydroxy  acids), 
(p.  206),  and  also  with  certain  unsaturated  compounds,  espe- 
cially in  the  presence  of  potassium  cyanide,  yielding  saturated 
nitriles  (Lapworth,  J.  C.  S.  1903,  995;  1904,  1214;  Knoe- 
venagel,  B.  1904,  37,  4065);  e.g.  a-phenylcinnamo-nitrile, 
CHPh:CPh.CN,  yields  diphenylsuccinylo-nitrile,  CN-CHPh- 
CHPh-CN. 

Hydrocyanic  acid  is  an  extremely  weak  monobasic  acid 
(K  =  0*0013  x  10~6),  and  its  salts  are  decomposed  even  by 
carbonic  acid.  It  is  a  typical  tautomeric  compound.  Its 
reduction  to  an  amine  and  its  hydrolysis  to  formic  acid  are 
similar  to  the  corresponding  reactions  of  methyl  cyanide,  and 
it  might  be  urged  that  these  reactions  favour  the  nitrile  for- 
mula H»CjN  Both  reactions  are,  however,  compatible  with 
the  view  that  it  has  the  carbylamine  structure  H-N:C.  The 
salts  are  usually  regarded  as  carbylamine  derivatives  (see 
derivatives  of  divalent  carbon,  Chap.  L,  D),  and  it  might  be 
argued  that  the  free  acid  has  a  similar  structure.  Such  an 
argument  is,  however,  unsound,  as  numerous  examples  are 
known  where  salts  have  a  structure  quite  different  from  that 
of  the  acid  from  which  they  are  prepared  (cf.  ethyl  aceto- 
acetate  and  pseudo  acids). 

Hydrocyanic  acid  can  be  detected  by  converting  it  either 
into  Prussian  blue  or  into  ferric  thiocyanate.  In  the  former 
case  the  solution  to  be  tested  is  treated  with  excess  of  caustic 
soda  and  some  ferrous  and  ferric  salt,  boiled,  and  acidified, 
when  Prussian  blue  results;  in  the  latter  the  solution  is 
evaporated  to  dryness  together  with  a  little  yellow  sulphide 


FERROCYANIDES   AND   FERRICYANIDES  269 

of  ammonium,  the  residue  taken  up  with  water  and  ferric 
chloride  added,  when  the  blood -red  colour  of  ferric  thio- 
cyanate  is  obtained. 

Trihydrocyanic  acid,  (CNH)X,  results  from  the  polymer- 
ization of  hydrocyanic  acid  under  certain  specified  conditions. 
It  forms  white,  acute-angled  crystals,  which  readily  yield  hy- 
drogen cyanide  when  heated  above  180°.  Its  molecular  weight 
is  still  unknown. 

Cyanides.— The  cyanides  of  the  alkali  and  alkali -earth 
metals  are  soluble  in  water,  and  the  solutions  have  a  strongly 
alkaline  reaction  due  to  the  hydrolysing  action  of  the  water 
(cf.  Soaps,  p.  159).  The  salts  of  the  heavy  metals,  with  the 
exception  of  mercuric  cyanide,  are  insoluble  in  water. 

Potassium  cyanide,  KCN,  forms  colourless  deliquescent 
cubes,  sparingly  soluble  in  alcohol.  The  commercial  product 
usually  contains  large  amounts  of  potassium  carbonate  due  to 
the  action  of  atmospheric  carbon  dioxide.  It  is  formed  when 
potassium  ferrocyanide  is  fused,  and  the  product  extracted 
with  water: 

K4FeC6N6  =  4KCN  +  FeC2  +  N2. 

Large  quantities  are  manufactured  by  Beilby's  process,  which 
consists  in  treating  a  fused  mass  of  potassium  carbonate  and 
carbon  with  ammonia,  the  product  being  a  molten  cyanide  of 
high  strength.  The  pure  salt  can  be  prepared  by  passing 
hydrogen  cyanide  into  an  alcoholic  solution  of  potassium 
hydroxide.  It  reacts  with  hydrogen  peroxide  in  two  different 
ways  (cf.  Masscrn,  J.  C.  S.  1907,  1449): 

1.  80  %   KCN  -f  H2O2  —  KCNO  +  H20  and 

KCNO  +  2H20  —  NH3  +  KOH  +  C02; 

2.  20  %   KCN  +  2H2O  — >  NH3  +  H-COOK. 

Mercuric  cyanide,  Hg(CN)2,  crystallizes  in  colourless  prisms, 
is  stable  in  the  air,  readily  soluble  in  water,  and  excessively 
poisonous.  Its  aqueous  solution  is  a  non-conductor  of  the 
electric  current,  and  does  not  give  the  ordinary  reactions  for 
a  mercuric  salt  or  for  a  cyanide  (cf.  B.  1908,  41,  317). 
Argentic  cyanide,  AgCN,  forms  a  white  flocculent  precipitate 
closely  resembling  argentic  chloride  in  appearance,  but  is 
soluble  in  hot  concentrated  nitric  acid. 

Complex  Cyanides. — The  double  cyanides,  which  are  pro- 
duced by  dissolving  the  insoluble  metallic  cyanides  in  a  solu- 
tion of  potassium  cyanide,  are  divided  into  two  classes.  Th(j 


270  XII.    CYANOGEN   COMPOUNDS 

members  of  the  one  class  are  decomposed  again  on  the  addition 
of  dilute  mineral  acids,  with  separation  of  the  insoluble  cyanide 
and  formation  of  hydrocyanic  acid,  e.g.  KAg(CN)2;  K2Ni(CN)4. 
The  members  of  the  other  class  are  much  more  stable,  do  not 
evolve  hydrocyanic  acid,  and  comport  themselves  as  salts  of 
particular  acids;  to  this  class  belong  potassium  ferrocyanide, 
K4Fe(CN)6,  [Fe(CN)2,  4KCN],  and  potassium  ferricyanide, 
K3Fe(CN)6,  [Fe(CN)3,  3KCN].  The  members  of  this  second 
class  are  often  termed  complex  salts,  and  are  the  metallic  salts 
of  complex  acids,  e.g.  hydroferrocyanic  acid,  H4FeC0N6,  and 
hydroferricyanic  acid,  H3FeC6N6,  which  are  formed  when  the 
salts  are  decomposed  with  mineral  acids.  Certain  salts  of  the 
latter  acid  are  not  decomposed  at  all  by  dilute  acids,  for  in- 
stance Prussian  blue,  but  they  are  by  caustic  potash  (which 
converts  Prussian  blue  into  Fe(OH)3  arid  K4FeC6N6). 

These  complex  salts,  as  a  rule,  do  not  give  the  reactions 
characteristic  of  simple  cyanides,  e.g.  white  precipitate  with 
silver-nitrate  solution,  owing  to  the  fact  that  in  solution  they 

do  not  yield  the  simple  cyanide  ions  CN  but  the  more  complex 

anions  FeC6N6  and  FeC6N6. 

Potassium  ferrocyanide,  yellow  prussiate  of  potash,  K4Fe(CN)6 
-f-  3H20,  may  be  obtained  by  adding  excess  of  potassium 
cyanide  to  a  solution  of  ferrous  sulphate,  or  by  dissolving 
iron  in  a  solution  of  cyanide  of  potassium,  when  hydrogen  is 
evolved,  thus: — 

2KCN  +  Fe  +  2H2O  =  Fe(CN)2  +  2KOH  -f  H2; 
Fe(CN)2  -f  4KCN  =  K4Fe(CN)6. 

The  old  commercial  method  consisted  in  fusing  together 
scrap-iron,  nitrogenous  organic  matter,  and  crude  potassic 
carbonate. 

It  is  now  usually  manufactured  from  the  hydrogen  cyanide 
present  in  crude  coal  gas  or  the  gas  from  coke  ovens.  The 
spent  oxide  used  in  the  purification  of  coal  gas  contains  Prus- 
sian blue  (ferric  ferrocyanide,  p.  271).  The  spent  oxide  is 
heated  with  hot  milk  of  lime,  and  the  Prussian  blue  thus 
transformed  into  calcium  ferrocyanide,  from  which  the  potas- 
sium salt  can  be  prepared. 

Another  method  consists  in  passing  the  coal  gas,  before  it 
has  been  subjected  to  dry  purification,  through  an  alkaline 
solution  containing  an  iron  salt.  The  sulphuretted  hydrogen 
reacts  with  the  iron  salt,  forming  ferrous  sulphide,  and  this 


FORROCYANIDES  AND  FERRICYANIDES 


271 


with  the  hydrogen  cyanide  and  alkali  (potassium  carbonate) 
yields  potassium  f errocyanide : 

FeS  +  6HCN  +  2K2CO3  =  K4FeC6N6  +  H2S  +  2CO2  +  2H2O. 

It  forms  large,  lemon-coloured  monoclinic  plates,  which  are 
stable  in  the  air  and  easily  soluble  in  water,  but  insoluble  in 
alcohol.  Concentrated  HC1  yields  hydro-ferrocyanic  acid, 
H4FeC6Ng,  in  the  form  of  white  needles.  With  a  solution 
of  CuS04,  a  red-brown  precipitate  of  cupric  ferrocyanide,  or 
Hatchetfs  brown,  CuJFeCgNg,  is  thrown  down,  and  with  solu- 
tions of  ferrous  and  ferric  salts  the  well-known  characteristic 
precipitates  (see  below).  Chlorine  oxidizes  it  to 

Potassium  ferricyanide,  red  prussiate  of  potash,  K3FeC6NG, 
thus : — 

2K4FeC6N6  +  C12  =  2K3FeC6N6  +  2KC1. 

This  crystallizes  in  long,  dark-red,  monoclinic  prisms  which 
are  readily  soluble  in  water.  The  solution  decomposes  when 
kept,  and  acts  as  a  strong  oxidizing  agent  in  the  presence  of 
alkali,  potassium  ferrocyanide  being  reproduced. 

Hydro-ferricyanic  acid,  H3FeC6N6,  forms  brown  needles, 
and  is  easily  decomposed 

FERRO-  AND  FERRI-CYANIDES  OF  IRON 


Ferrocyanides. 

Ferricyanides. 

Ferrous  salts, 

Potassium-ferro-ferrocyanide, 
K2Fe«(FeCgN6)*,  fromFeS04 
+  KjFeCsNe;  white,  becom- 
ing rapidly  blue  in  the  air 
from  conversion  into 

TurribulVs  blue, 
Fe3ii(FeC6N«)2iil,  from 
FeS04    (excess)    + 

i 

Ferric  salts, 

Potassium  -ferri  -  ferrocyanide, 
KFe^FeCeNe),  or  soluble 
Prussian  blue,  which  is  also 
formed  from  ferrous  sul- 
phate with  an  excess  of 
potassic  ferricyanide. 

(FeCls-t-  K3FeC6N«give 
no  .  precipitate,  but 
only  a  brown  color- 
ation.) 

Insoluble  Prussian  blue 
or  Williamson's  blue, 
Fe4iii(FeC6N6)3iv,  from  FeCl8 
+  K4FeC6N6;  blue  powder 
with  a  copper  glance. 

272  XII.   CYANOGEN  COMPOUNDS 

The  formation  of  Prussian  blue  was  first  observed  by 
Diesbach  about  the  year  1700. 

As  regards  the  constitution  of  hydro-ferro-  and  hydro-ferri- 
cyanic  acids,  one  may  make  the  assumption  that  they  contain 
the  tervalent  radical,  (C3N3)Ui,  "  tricyanogen  ",  of  cyanuric 
acid  (see  p.  272): 


Potassium  ferrocyanide  Potassium  ferricyanide. 


Turnbull's  blue. 

When  ferrocyanide  of  potassium  is  oxidized  by  nitric  acid, 
nitro  -  prussic    acid   is   formed,   the   sodium   salt  of  which, 


-+-  2H20,  crystallizes  in  red  prisms  soluble 
in  water.  It  forms  a  valuable  reagent  for  the  detection  of 
sulphuretted  hydrogen,  an  alkaline  solution  yielding  with  the 
latter  a  splendid  but  transient  violet  coloration. 

B.  Halogen  Compounds  of  Cyanogen 

Cyanogen  chloride,  C1»N:0  (Berthollet),  is  a  colourless  con- 
densable gas  of  a  most  obnoxious  pungent  odour,  is  somewhat 
soluble  in  water,  and  boils  at  15  -5°.  It  is  prepared  by  the 
action  of  chlorine  upon  mercuric  cyanide  or  upon  dilute 
aqueous  hydrocyanic  acid,  CNH  +  C12  =  CNC1  +  HC1.  It 
polymerizes  readily  to  cyanuric  chloride,  and  yields  sodium 
chloride  and  cyanate  with  aqueous  sodium  hydroxide: 

CN.Cl  +  2NaOH  =  CN-ONa  +  ClNa  -f  H2O. 

Cyanogen  bromide,  CNBr,  forms  transparent  prisms,  and 
is  prepared  by  the  action  of  sulphuric  acid  on  a  mixture  of 
bromate,  bromide,  and  cyanide  of  sodium: 

5HBr-f  3HCN  =  SBrCN  +  3HBr  +  3H2O. 


Cyanogen  iodide,  ONI,  forms  beautiful  white  prisms,  smelling 
intensely  both  of  cyanogen  and  iodine,  and  subliming  with  the 
utmost  ease.  (For  constitution  cf.  Chattaway  and  PFadmore, 
J.  C.  S.  1902,  191.) 

Cyanuric  chloride,  trichlorocyanogen,  (CC1)3N3,  is  obtained 
from  cyanogen  chloride,  or  from  hydrocyanic  acid  and  chlor- 
ine in  ethereal  solution.  It  forms  beautiful  white  crystals  of 
a.n  unpleasant  pungent  odour,  melts  at  145°,  and  boils  at 


CYANIC  AND  CYANURIC  ACIDS  273 

190°.  Boiling  water  decomposes  it  with  formation  of  hydro- 
gen chloride  and  cyanuric  acid 

C.  Cyanic  and  Cyanurie  Acids 

Cyanuric  acid  is  formed  when  urea  is  heated,  either  alone 
or  in  a  stream  of  chlorine  gas;  and  when  this  acid  is  distilled, 
and  the  vapour  condensed  in  a  freezing-mixture,  cyanic  acid, 
CNOH,  is  obtained  as  a  mobile  liquid  of  a  pungent  odour: 

CaNsOaHg  =  3  CNOH 

It  is  exceedingly  unstable;  when  taken  out  of  the  freezing- 
mixture  it  changes,  with  explosive  ebullition,  into  a  white 
porcelain-like  mass  which  consists  of  cyanuric  acid  70  per  cent, 
and  cyamelide  30  per  cent.  Potassium  cyanate,  CNOK,  fre- 
quently also  termed  potassium  isocyanate,  is  prepared  by  the 
oxidation  of  an  aqueous  solution  of  potassium  cyanide  b" 
means  of  permanganate  (A.  259,  377);  or  by  fusing  potassium 
cyanide  or  yellow  prussiate  of  potash  with  Pb02  or  Mn02: 
(CNK  +  0  =  CNOK).  It  crystallizes  in  white  plates,  readily 
soluble  in  water  and  alcohol.  Ammonium  cyanate,  CNO 
(NH4),  forms  a  white  crystalline  mass,  and  is  of  especial 
interest  on  account  of  the  readiness  with  which  it  changes 
into  the  isomeric  urea,  CO(NH2)2  (p.  281). 

When  these  salts  are  decomposed  with  mineral  acids,  free 
cyanic  acid  is  not  formed,  but  its  products  of  hydrolysis,  viz. 
carbon  dioxide  and  ammonia : 

CONH  +  H20  =  C02  +  NH3. 

This  decomposition  is  avoided  by  the  addition  of  dilute  acetic 
acid  (instead  of  hydrochloric),  but  in  the  latter  case  the  cyanic 
acid  changes  into  its  polymer  cyanuric  acid,  and  the  hydrogen- 
potassium  salt  of  the  latter  slowly  crystallizes  out. 

When  the  hydrogen  atom  in  the  cyanic  acid  molecule  is 
replaced  by  alkyl  radicals,  two  distinct  groups  of  compounds 
are  possible.  The  derivatives  which  are  constituted  on  the 
type  N;C«CKR  are  termed  the  normal,  and  those  on  the  type 
0:C:N»R  the  iso-compounds. 

Ethyl  isocyanate,  cyanic  ether,  0 :  C :  N  •  CH2  •  CH3,  obtained 
when  potassium  cyanate  is  distilled  with  ethyl  iodide  or 
potassium  ethyl-sulphate,  is  a  colourless  liquid  of  suffocating 
odour,  distilling  at  60°,  and  is  decomposed  by  water.  It  does 

(B480)  S 


274  XIL  CYANOGEN  COMPOUNDS 

not  behave  as  a  typical  ester,  since  when  hydrolysed  with  acids 
or  alkalis  it  yields  ethylamine  and  carbon  dioxide: 


Water,  which  acts  in  a  similar  manner,  gives  rise  to  the 
more  complicated  urea  derivatives;  ammonia  and  amines  also 
produce  derivatives  of  urea,  and  alcohol  yields  derivatives  of 
carbamic  acid  (see  Carbonic  Acid  Derivatives). 

The  production  of  ethylamine  as  one  of  the  products  of 
hydrolysis  is  usually  regarded  as  a  strong  argument  in  favour 
of  the  view  that  in  the  original  isocyanate  the  ethyl  group 
is  attached  to  nitrogen  and  not  to  oxygen,  e.g.  0:C:N-Et. 
It  is  questionable,  however,  whether  free  cyanic  acid  and 
cyanate  of  potassium  possess  analogous  constitutions,  since 
frequent  observations  have  shown  that  the  normal  cyanic 
compounds  readily  change  into  the  iso-  (see  below)  ;  theoretical 
considerations  indeed  make  it  more  probable  that  cyanic  acid 
has  the  constitution  N|C«OH,  according  to  which  it  appears 
as  the  normal  acid,  with  cyanogen  chloride  as  its  chloride. 

Normal  cyanic  esters  are  not  known  (cf.  A.  287,  310). 

Cyanuric  acid,  C3N303H3,  =  (CN)3(OH)3  (Scheele),  obtained 
by  heating  urea,  or  by  the  action  of  water  on  cyanuric  chloride, 
forms  transparent  prisms  containing  two  molecules  of  water  of 
crystallization.  It  effloresces  in  the  air,  and  dissolves  readily 
in  hot  water.  It  is  a  tribasic  acid.  The  sodium  salt  is  spar- 
ingly soluble  in  cone.  NaOH;  the  (Cu-NH4)  salt  possesses  a 
characteristic  beautiful  violet  colour.  Upon  prolonged  boiling 
with  hydrochloric  acid  it  is  hydrolysed  to  C02  and  NH3,  while 
phosphorus  pentachloride  converts  it  into  cyanuric  chloride. 

Only  one  cyanuric  acid  is  known,  and  owing  to  the  fact 
that  the  N-methyl  derivative  is  obtained  by  the  action  of 
diazo-methane  is  represented  by  the  iso-structure  : 


(Compare  also  Hantzsch,  B.  1906,  39,  139). 

Cyanuric  acid  is  a  pseudo  acid,  as  its  salts  and  also  chloride 
have  the  normal  structure.  The  mercuric  salt  exists  in  two 
isomeric  forms. 

Two  distinct  groups  of  alkyl  derivatives  are,  however, 
known  —  normal  cyanuric  esters,  e.g.  ethyl  cyanurate, 


ISO-THIOCYANATES  275 

which  is  formed  by  the  action  of  ethyl  iodide  on  silver  cyanu- 
rate  at  the  ordinary  temperature,  or  by  the  action  of  sodium 
ethoxide  on  cyanogen  chloride  or  cyanuric  chloride,  is  readily 
changed  into  an  isocyanuric  ester,  e.g.  ethyl  isocyanurate, 


These  isocyanurates  are  often  formed  instead  of  the  normal 
compounds  if  the  temperature  is  not  kept  low,  e.g.  when  a 
cyanurate  is  heated  with  potassium  ethyl-sulphate.  They  are 
further  formed  by  the  polymerization  of  the  isocyanic  esters, 
oeing  thus  obtained  as  by-products  in  the  preparation  of  the 
latter. 

The  constitution  of  the  normal  compounds  is  largely  based 
on  the  fact  that  on  hydrolysis  they  behave  as  normal  esters 
and  yield  ethyl  alcohol  and  cyanuric  acid.  The  isocyanurates, 
on  the  other  hand,  usually  yield  primary  amines,  e.g.  ethyl- 
amine,  and  hence  presumably  the  alkyl  group  is  attached  to 
nitrogen  in  the  isocyanurate  molecule. 

For  mixed  normal  iso-esters,  see  Hantzsch  and  Bauer,  B. 
1905,  38,  1005. 

D.  Thioeyanic  Acid  and  its  Derivatives 

Nearly  every  oxygen  derivative  of  cyanogen  has  a  sulphur 
analogue.  As  examples,  we  have  the  salts  of  thiocyamc 
acid. 

Potassium  thiocyanate,  -sulphocyanate,  -sulphocyanide,  -rhod- 
anide,  CNSK,  is  readily  formed  when  potassium  cyanide  is 
fused  with  sulphur,  or  when  an  aqueous  solution  of  KCN 
is  evaporated  with  yellow  ammonium  sulphide. 

It  is  usually  prepared  by  fusing  potassium  ferrocyanide  with 
sulphur  and  potashes.  It  forms  long  colourless  deliquescent 
prisms,  extremely  soluble  in  water  with  absorption  of  much 
heat,  and  also  readily  soluble  in  hot  alcohol.  Ammonium 
thiocyanate,  CNS(NH4),  is  formed  when  a  mixture  of  carbon 
disulphide,  concentrated  ammonia,  and  alcohol  (Millori)  is 
heated,  dithiocarbamate  and  trithiocarbonate  of  ammonia 
being  formed  as  intermediate  products: 

=  CNSH  +  H2S. 


It  forms  colourless  deliquescent  plates,  readily  soluble  in 
alcohol,  and  when  heated  to  130°-140°  is  partially  transformed 


276  XII.   CYANOGEN  COMPOUNDS 

into  the  isomeric  thio-urea,  just  as  ammonium  cyanate  is  into 
urea.  It  precipitates  silver  thiocyanate,  CNSAg  (white),  from 
solutions  of  silver  salts,  and  is  therefore  employed  in  the 
titration  of  silver,  with  ferric  sulphate  as  indicator;  and  it 
gives  with  ferric  salts  a  dark  blood -red  coloration  of  am- 
monium ferrithiocyanate,  2Fe(CNS)8,  9NH4CNS,  4H20. 
This  last  reaction  is  exceedingly  delicate.  Mercurous  thio- 
cyanate, HgCNS,  is  a  white  powder  insoluble  in  water,  which 
increases  enormously  in  volume  upon  being  burnt  (Pharaoh's 
serpents).  The  free  thiocyanic  acid,  CNSH,  as  obtained  by 
decomposing  the  mercurous  salt  with  hydrochloric  acid,  is  a 
pale-yellow  liquid  of  pungent  odour,  but  when  pure  is  a 
colourless  solid,  m.-pt.  5°.  The  acid  and  its  salts  appear  to 
have  the  normal  structure  H»S'C|N.  At  the  ordinary  tem- 
perature it  polymerizes  to  a  yellow  amorphous  substance,  and 
decomposes  in  concentrated  aqueous  solution,  with  formation 
of  persulphocyanic  acid,  C2N2S3H2  (yellow  crystals). 

Concentrated  sulphuric  acid  decomposes  the  thiocyanates 
with  formation  of  carbon  oxy  -  sulphide :  CNSH  +  H20 
=  COS-f  NH3;  sulphuretted  hydrogen  decomposes  them  into 
carbon  disulphide  and  ammonia :  CNSH  +  H2S  =  CS2  +  NH3. 

The  alkyl  derivatives  of  thiocyanic  acid  exist  in  two  distinct 
forms,  corresponding  with  the  normal  and  iso-cyanates. 

Normal  Thiocyanates. — Ethyl  thiocyanate,  N:C-S.CH2. 
CH3,  is  obtained  either  (1)  by  the  distillation  of  potassium 
ethyl -sulphate  with  potassium  thiocyanate,  or  (2)  by  the 
action  of  cyanogen  chloride  upon  ethyl  mercaptide.  It  is  a 
colourless  liquid  with  a  peculiar  pungent  odour  of  leeks,  boils 
at  142°,  and  is  almost  insoluble  in  water.  Alcoholic  potash 
hydrolyses  it  in  the  normal  manner,  yielding  ethyl  alcohol 
and  potassium  thiocyanate;  in  other  reactions,  however,  the 
alkyl  radical  remains  united  to  sulphur;  thus  nascent  hydro- 
gen reduces  it  to  mercaptan,  and  fuming  nitric  acid  oxidizes  it 
to  ethyl-sulphonic  acid. 

These  reactions,  combined  with  its  formation  from  a  mer- 
captide, indicate  that  the  ethyl  group  is  directly  attached  to 
sulphur,  viz.  C2H5-S-C:N. 

Allyl  thiocyanate,  NjC«S«C3H5,  is  a  colourless  liquid  smell- 
ing of  leeks.  It  boils  at  161°,  and  when  distilled  is  converted 
into  the  isomeric  mustard  oil. 

The  iso-thiocyanates  are  usually  known  as  mustard  oils, 
and  are  more  stable  than  the  normal  thiocyanates.  They 
contain  the  alkyl  radical  attached  to  nitrogen,  and  not  to 


CYANAMIDE  AND  ITS  DERIVATIVES  277 

sulphur  (cf.  Isocyanates),  since  on  hydrolysis  they  yield 
primary  amines,  e.g. : 

S:C:NEt  +  2H20  =  H2S  +  C02  +  NH2Et, 
and  also  on  reduction: 

S:C:NEt-f  4H  =  NH2Et  +  CH2S. 

The  thiomethylene  formed  in  this  last  reaction  immediately 
polymerizes  to  (CH2S)3.  The  commonest  iso-thiocyanate  is 
allyl  mustard  oil,  commonly  known  as  mustard  oil,  since  the 
odour  and  taste  of  mustard  seeds  (Sinapis  niger)  are  due  to 
this  compound.  It  does  not  exist  as  such  in  the  seeds,  but 
is  formed  from  a  glucoside,  potassium  myronate,  when  the 
seeds  are  pulverized  and  left  in  contact  with  water.  The 
reaction  is  a  process  of  fermentation,  and  is  due  to  the 
presence  of  an  enzyme,  myrosin,  in  the  seeds: 

C10H18010NS2K  =  C6H12Ofl  +  KHS04  +  SCNC3H6. 

It  is  a  liquid  sparingly  soluble  in  water  and  of  exceedingly 
pungent  odour,  which  produces  blisters  on  the  skin,  and  boils 
at  151°.  It  is  also  obtained  by  distilling  allyl  thiocyanate, 
owing  to  a  molecular  rearrangement,  or  by  the  action  of 
carbon  disulphide  upon  allylamine: 

CS2  +  NH2.C3H6  =  CS:N.C3H6  +  H2S. 

This  reaction  proceeds  in  two  stages,  a  dithiocarbamate, 
C3H5NH.CS.SNH3C3H5,  the  allylamine  salt  of  allyl-dithio- 
carbamic  acid  being  first  formed,  and  this  is  changed  into  allyl 
iso-thiocyanate  when  distilled  with  mercuric  chloride.  (See 
Dithiocarbamic  acid,  p.  296.) 

Ethyl  iso-thiocyanate,  C2H5N:CS  (b.-pt.  134°),  and  methyl 
iso-thiocyanate,  CH3N:CS  (solid,  m.-pt.  34°,  b.-pt.  119°),  &c., 
closely  resemble  the  allyl  compound,  and  are  obtained  in  an 
analogous  manner  by  the  action  of  carbon  disulphide  upon 
ethylamine,  methylamine,  &c. 

The  mustard  oils  are  also  obtained  by  distilling  alkylated 
thio-ureas  (p.  297)  with  syrupy  phosphoric  acid  (Hofmann, 
B.  15,  985),  or  with  concentrated  hydrochloric  acid. 

E.  Cyanamide  and  its  Derivatives 

The  Amide  of  Cyanic  Acid.— Cyanamide,  N;C.NH2,  is 
formed  by  leading  cyanogen  chloride  into  an  ethereal  solution 


278  XII.   CYANOGEN  COMPOUNDS 

of  ammonia,  CNC1  +  2NH8  =  CN-NH2  +  NH4C1,  or  by 
the  action  of  HgO  upon  thio-urea  in  aqueous  solution  ("de- 
sulphurization"),  NH2.CS-NH2  -  NC-NH^  +  H2S. 

It  is  a  colourless  crystalline  hygroscopic  mass,  readily 
soluble  in  water,  alcohol,  and  ether.  It  melts  at  40°,  and 
when  heated  to  150°  changes  into  the  polymeric  dicyan-diamide 
with  explosive  ebullition;  the  same  change  occurs  on  evaporat- 
ing its  solution  or  allowing  it  to  stand.  Dilute  acids  cause  it 
to  take  up  the  elements  of  water,  with  formation  of  urea : 

N:C-NH 


NH2; 

and  it  combines  in  an  analogous  manner  with  hydrogen  sul- 
phide to  thio-urea.  When  heated  with  ammonium  salts,  it 
yields  salts  of  guanidine. 

Cyanamide  behaves  as  a  weak  base,  forming  crystalline, 
easily  decomposable  salts  with  acids  and,  at  the  same  time, 
as  a  weak  acid,  yielding  a  sodium  salt,  CN»NHNa,  a  lead 
and  a  silver  salt,  &c.  The  last  is  a  yellow  powder,  and  has 
the  composition  CN2Ag2. 

The  calcium  derivative  of  cyanamide,  N;C»NOa,  is  manu- 
factured for  use  as  a  fertilizer,  as,  in  the  soil,  the  nitrogen  be- 
comes available  for  the  plant  in  the  form  of  ammonia.  It  is 
manufactured  by  passing  air  or  nitrogen  over  calcium  carbide 
at  about  800°-1000°, 

CaC2  +  N2  =  CaCN2  +  C, 

or  by  passing  nitrogen  over  a  mixture  of  lime  and  carbon 
heated  to  2000°.  An  excess  of  carbon  is  used,  and  the  crude 
product,  which  forms  a  black  powder,  contains  14-23  per  cent 
of  nitrogen  (cf.  Abs.  1904,  i.  562).  The  presence  of  a  small 
amount  of  calcium  chloride  accelerates  the  absorption  of  nitro- 
gen by  calcium  carbide. 

Cyanamide  also  gives  rise  to  two  isomeric  series  of  alkyl 
derivatives. 

1.  Methyl-  and  ethyl-cyanamides  are  prepared  from  methyl 
and  ethyl  thio-urea.  Diethyl-cyanamide,  CN2(C2H5)2,  and  its 
homologues  are  obtained  by  the  action  of  alkyl  iodides  or  sul- 
phates on  crude  calcium  cyanamide  (B.  1911,  44,  3149).  Acids 
hydrolyse  the  ethyl  compound  to  C02,  NH3,  and  NH(C2H5)2, 
hence  it  possesses  the  constitution  N  •  C  •  N(C2H6)2 : 

N!C.N(C2H6)2  +  2H20  =  NH3  +  C02  +  NH(C2H5)2. 


CARBONIC  ACID  DERIVATIVES  279 

2.  Other  cyanamide  derivatives,  which  are  chiefly  known  in 
the  aromatic  series,  are  derived  from  a  hypothetical  isomer 
of  cyanamide,  viz.  carbo-di-imide,  NH:C:NH;  for  instance, 
diphenyl-carbodiimide,  CN2(C6H5)2.  Boiling  with  acids  like- 
wise decomposes  them  into  C02  and  an  amine,  but  the  latter 
can  only  be  a  primary  one. 


XIII.   CARBONIC  ACID  DERIVATIVES 

Carbonic  acid  is  a  dibasic  acid,  forming  two  series  of 
salts,  e.g.  Na2C03  and  NaHC03.  The  acid  itself,  C03H2, 

=   0»*XVvTT,   is   unknown,  but  may  be  supposed  to  exist 

in  the  aqueous  solution.  It  is  the  lowest  hydroxy-acid 
CnH2n03,  i.e.  it  is  homologous  with  gly collie  acid,  and  may 
be  regarded  as  hydroxy-formic  acid.  As  both  hydroxyls  are 
linked  to  the  same  carbon  atom,  the  non-existence  of  the  free 
hydrate  is  readily  understood  (see  p.  124,  &c.). 

The  salts  of  carbonic  acid  and  several  simple  derivatives  of 
carbon  are  usually  treated  of  under  inorganic  chemistry.  The 
esters,  chlorides,  and  amides  of  carbonic  acid,  like  the  salts, 
form  two  series.  The  normal  compounds,  e.g.  CO(OC2H5)2, 
ethyl  carbonate,  COCL,  carbonyl  chloride,  and  CO(NH2)2, 
carbamide  or  urea,  are  well  characterized,  and  are  very  similar 
to  those  of  oxalic  or  succinic  acid;  the  acid  compounds,  e.g. 
OH.CO.OC2H5,  ethyl  hydrogen  carbonate,  OH.CO.C1,  chloro- 
carbonic  or  chloroformic  acid,  and  OH-CO-NH2,  carbamic 
acid,  on  the  other  hand,  are  unstable  in  the  free  state,  but 
form  stable  salts.  Many  mixed  derivatives  are  known,  e.g. 
ethyl  carbamate,  NH2  •  CO  •  OEt,  which  is  an  ester  and  an 
acid  amide,  analogous  to  oxamethane  (p.  236);  C1-CO'OC2H5, 
ethyl  chloro-carbonate,  which  is  an  ester  and  an  acid  chloride. 

A.  Esters 

Ethyl  carbonate,  CO(OC2H5)2,  is  formed  by  the  action  of 
ethyl  iodide  upon  silver  carbonate,  or  by  the  action  of  alcohol 
upon  ethyl  chloro-carbonate,  and  therefore  indirectly  from 
carbon  oxy-chloride  and  alcohol: 

CO(OC2H6)2  + 


280  XIII.   CARBONIC  ACID  DERIVATIVES 

It  is  a  neutral  liquid  of  agreeable  odour,  lighter  than  water, 
and  boils  at  126°. 

Analogous  methyl  and  propyl  esters  are  known,  and  also 
esters  containing  two  different  alkyl  groups.  It  is  a  matter 
of  no  consequence  which  of  these  radicals  is  introduced  first 
into  the  molecule,  a  proof  of  the  symmetrical  arrangement  of 
the  two  hydroxyls. 

Ethyl  hydrogen  carbonate,  HO  •  CO  •  0  •  C2H5,  a  type  of  an 
acid  ester,  corresponds  exactly  with  ethyl  hydrogen  sulphate, 
but  is  much  less  stable,  and  only  known  in  its  salts.  Potas- 
sium ethyl  carbonate,  KO'CO»OC2H5,  is  obtained  by  passing 
C02  into  an  alcoholic  solution  of  potassic  ethoxide:  C02 
+  KOC2H5  =  COS(C2H5)K.  It  crystallizes  in  glistening 
mother-of-pearl  plates,  but  is  decomposed  by  water  into 
potassium  carbonate  and  alcohol. 

B.  Chlorides  of  Carbonic  Acid 

Carbon  oxy  -  chloride,  Carbonyl  chloride,  phosgene,  COC12 
(/.  Davij),  is  the  true  chloride  of  carbonic  acid  and  is  analogous 
to  sulphuryl  chloride,  S02C12.  It  is  obtained  by  the  direct 
combination  of  carbon  monoxide  and  chlorine  in  sunlight,  and 
also  by  the  oxidation  of  chloroform  by  means  of  chromic  acid. 
It  is  a  colourless  gas,  condensing  to  a  liquid  below  +8°,  of 
exceptionally  suffocating  odour,  and  is  readily  soluble  in 
benzene  or  toluene.  As  an  acid  chloride  it  decomposes 
violently  with  water  into  C02  and  HC1.  It  therefore  trans- 
forms hydrated  acids  into  their  anhydrides,  with  separation 
of  water,  and  converts  aldehyde  into  ethylidene  chloride.  It 
yield  urea  derivatives  with  secondary  amines  of  the  fatty 
series,  and  carbamic  chlorides  with  secondary  amines  of  the 
aromatic  (B.  20,  783). 

Chloro-carbonic  acid,  Chloro-formic  acid,  Cl-CO-OH,  the 
half  acid  chloride  of  carbonic  acid,  is  analogous  to  chloroxalic 
acid  (p.  234),  but  is  so  unstable  that  it  is  unknown  in  the  free 
state.  Its  esters,  however,  e.g.  ethyl  chloro-carbonate,  ethyl 
chloro-formate,  C1.CO-OC2H5,  may  be  prepared  by  the  action 
of  carbon  oxy-chloride  upon  alcohols  (Dumas,  1833): 


COC12  +  C2H6OH  =  C1.CO.OC2H6 

The  ethyl  ester  is  a  volatile  liquid  of  very  pungent  odour, 
which  boils  at  93°.    It  reacts  as  an  acid  chloride,  being  decom- 


AMIDES   OF  CARBONIC  ACID  281 

posed  by  water,  and  is  specially  fitted  to  effect  the  synthetical 
entrance  of  the  carboxyl  group  into  many  compounds. 

The  esters  and  acid  chlorides  just  described  are  derived 
from  ordinary  carbonic  acid,  H2C03,  the  analogue  of  meta* 
silicic  acid,  H2Si03.  Although  an  ortho-carbonic  acid  itself, 
C(OH)4,  is  unknown,  certain  derivatives  are  readily  prepared. 
Carbon  tetrachloride  may  be  regarded  as  the  chloride  of 
ortho-carbonic  acid.  It  is  much  more  stable  than  ordinary 
acid  chlorides,  and  at  high  temperatures  only  is  it  decomposed 
by  alkalis,  yielding  alkali  chloride  and  carbonate. 

The  esters  of  ortho-carbonic  acid,  e.g.  ethyl  ortho-carbonate, 
C(OC2H5)4,  are  readily  obtained  by  the  action  of  sodium  alco- 
holates  on  chloropicrin  (p.  97).  They  are  colourless  oils  with 
fragrant  odours.  The  ethyl  ester  boils  at  158°,  and  the  propyl 
at  224°.  When  hydrolysed,  they  yield  an  alkali  carbonate  and 
the  alcohol. 

C.  Amides  of  Carbonic  Acid 

The  normal  amide  of  carbonic  acid  is  urea  or  carbamide, 
NH2'CO'NH2,  the  amic  acid  is  carbamic  acid,  HO»CO»NH2. 
Imido-carbonic  acid,  HN:C(OH)2,  would  be  an  imide  of  car- 
bonic acid,  but  it  is  only  known  in  its  derivatives  (Sandmeyer, 
B.  19,  862). 

The  amidine  of  carbonic  acid  is  guanidine.  The  "ortho- 
amide"  of  carbonic  acid,  which  would  possess  the  formula 
C(NH2)4,  is  unknown;  when  it  might  be  expected,  guanidine 
and  ammonia  are  formed  instead. 

The  modes  of  formation  of  urea  and  of  carbamic  acid  are 
exactly  analogous  to  those  of  the  amides  in  general: 

1.  By  the  action  of  ammonia  upon  ethyl  carbonate: 


CO(OC2H6)2  +  2NH3  =  CO(NH2)2  +  2C2H6-OH. 
CO(OC2H5)2  +    NH3 


2.  By  the  abstraction  of  the  elements  of  water  from  car- 
bonate or  carbamate  of  ammonia.  Dry  carbon  dioxide  and 
ammonia  combine  together  directly  to  ammonium  carbamate, 
the  so-called  anhydrous  carbonate  of  ammonia,  NH2.COj 
ONH4,  which  is  transformed  into  urea  when  heated  to  135°, 
or  when  exposed  to  the  action  of  an  alternating  current  of 
electricity  : 

NH2.CO-ONH4  =  CO(NH2)2  +  H20. 


282  XIII.   CARBONIC  ACID  DERIVATIVES 

3.  By  the  action  of  ammonia  upon  carbonyl  chloride  and  its 
derivatives : 

COCl2-f4NH3  =  CO(NH2)2  +  2NH4C1. 
CO(OC2H6)C1  +  2NH3  =  CO(OC2H5)NH2  +  NH4C1. 

Carbamic  acid,  NH2.CO«OH,  is  known  only  in  the  form 
of  derivatives;  the  ammonium  salt,  NH2»CO'ONH4,  forms  a 
white  mass,  and  dissociates  at  60°  into  2NH3  +  C02.  Its 
aqueous  solution  does  not  precipitate  a  solution  of  calcic 
chloride  at  the  ordinary  temperature,  since  calcic  carbamate 
is  soluble  in  water;  but  when  boiled  it  is  hydrolysed  to  the 
carbonate,  and  calcic  carbonate  is  then  thrown  down. 

Urethane,  Ethyl  carbamate,  NH2  •  CO  •  OC2H5,  is  formed 
according  to  method  3,  and  by  the  direct  union  of  cyanic 
acid  with  alcohol;  also  from  urea  nitrate  and  sodium  nitrite 
in  presence  of  alcohol.  It  forms  large  plates,  is  readily 
soluble  in  water,  melts  at  50°,  and  boils  at  184°.  It  acts 
as  a  soporific,  and  on  hydrolysis  with  alkali  yields  the  alkali 
carbonate,  ammonia  and  ethyl  alcohol.  One  of  its  hydrogen 
atoms  is  replaceable  by  sodium.  Urethane  may  be  employed 
instead  of  cyanic  acid  for  certain  synthetic  reactions  (B.  23, 
1856). 

Analogous  methyl  and  propyl  esters  of  carbamic  acid  are 
known,  and  are  also  termed  urethanes. 

Carbamic  chloride,  NH2'CO»C1,  obtained  by  the  action  of 
hydrogen  chloride  upon  cyanic  acid  (Wohler,  A.  45,  357),  and 
of  carbonyl  chloride  upon  ammonium  chloride  at  400°,  forms 
long,  compact,  colourless  needles  of  pungent  odour.  M.-pt.  50°, 
b.-pt.  61°-62°.  It  reacts  violently  with  water,  amines,  &c.,  and 
serves  for  the  synthesis  of  organic  acids  (see  these). 

Ethyl  imido-dicarboxylate,  NH(C02C2H5)2,  is  the  imide 
corresponding  with  the  amide  urethane.  It  may  be  prepared 
from  the  sodium  compound  of  urethane  and  ethyl  chloro- 
carbonate.  It  forms  colourless  crystals,  melting  at  50°.  By 
the  exchange  of  one  ethoxy  (OC2H5)  group  for  an  amido  (NH2) 
group,  it  gives  rise  to  allophanic  ester,  and  by  the  exchange  of 
two,  to  biuret  (see  p.  289). 

Urea,  Carbamide,  CO(NH2)2,  was  first  found  in  urine  in 
1773.  It  is  contained  in  the  urine  of  mammals,  birds,  and 
some  reptiles,  and  also  in  other  animal  fluids.  An  adult  man 
produces  about  30  gms.  daily,  and  it  may  be  regarded  as  the 
final  decomposition  product  formed  by  the  oxidation  of  the 
nitrogenous  compounds  in  the  organism. 


tJREA  283 


It  may  be  prepared  by  the  action  of  ammonia  on  ethyl  car- 
bonate, ethyl  carbamate,  or  phosgene,  and  synthetically  by  the 
molecular  transformation  of  ammonium  cyanate,  by  warming 
its  aqueous  solution  or  allowing  it  to  stand  (cf.  pp.  1  and  273): 

N:C-ONH4  ^± 


The  reaction  is  reversible,  and  hence  the  process  is  never 
complete.  When  equilibrium  is  reached,  only  a  very  small 
amount  of  untransformed  cyanate  is  left,  and  the  equilibrium 
is  practically  independent  of  the  temperature.  The  reaction 
has  been  shown  to  be  a  typical  bimolecular  one  (Walker  and 
Hambly,  J.  C.  S.  1895,  746). 

The  reaction  is  represented  as  follows  by  Chattaway  (P.  1911. 
27,  281): 


NH4-N:C:O  -*  HN:C:0  + 

HN:C(OH)NH2  -* 

It  is  usually  prepared  by  mixing  a  solution  of  potassium 
cyanate  (from  the  ferrocyanide)  with  ammonium  sulphate  and 
evaporating  the  mixture  (ammonium  cyanate  is  first  formed 
and  gradually  changes  to  urea),  or  by  evaporating  urine,  add- 
ing nitric  acid,  and  decomposing  the  separated  and  purified 
nitrate  of  urea  by  barium  carbonate. 

It  is  also  formed  by  heating  a  solution  of  carbon  monoxide 
in  ammoniacal  cuprous  chloride: 

CO  +  2NH3  -{-  Cu2Cl2  =  CO(NH2)2  +  2HC1  +  2Cu. 

It  crystallizes  in  long  rhombic  prisms  or  needles,  has  a 
cooling  taste,  is  very  readily  soluble  in  water,  also  in  alcohol, 
but  not  in  ether.  It  melts  at  132°,  sublimes  in  vacuo  without 
decomposition,  and  when  strongly  heated  yields  ammonia, 
cyanuric  acid,  biuret,  and  ammelide.  As  an  amide  it  is 
readily  hydrolysed  by  boiling  with  alkalis  or  acids,  or  by 
superheating  with  water  (cf.  Fawsitt,  J.  C.  S.  1904,  1581; 
1905,  494): 

CO(NH2)2 


Nitrous   acid  reacts  with  it  to  produce  carbon  dioxide, 
nitrogen,  and  water: 

CO(NH2)2  +  2N02H  =  C02  +  2N2  +  3H20. 


Sodium  hypochlorite  and  hypobromite  act  in  a  similar 
manner  (Davy,  Knop).  Hufner's  method  of  estimating  urea 
quantitatively  depends  upon  the  measurement  of  the  nitrogen 


284  XIII.   CARBONIC  ACID  DERIVATIVES 

thus  obtained  (J.  pr.  Ch.,  [2],  3,  1  ;  cf.  also  B.  24,  Ref.  330). 
Urea  also  reacts  with  bromine  and  alkalis  in  much  the  same 
manner  as  the  lower  acid  amides  (Hofmann  reaction,  p.  184), 
yielding  carbon  dioxide  and  the  corresponding  amine,  hydra- 
zine  (C.  C.  1905,  i,  1227),  which  is  best  removed  by  the  addi- 
tion of  benzaldehyde. 

Urea  reacts  with  an  aqueous  solution  of  chlorine,  yielding 
the  dichloro-derivative  CO(NHC1)2.  With  acids  this  forms 
nitrogen  trichloride,  and  with  ammonia  it  yields  diurea  or 


paraurazine,  CO^^00  (Chattaway>  J-  c-  s-  1909> 


129,  235).  When  warmed  with  alcoholic  potash  to  100°,  urea 
is  converted  into  cyanate  of  potassium  and  ammonia. 

The  basic  character  of  the  amino  groups  is  greatly  weakened 
in  urea  by  the  presence  of  the  negative  carbonyl.  Among 
the  salts  of  urea  with  acids  may  be  mentioned  urea  nitrate, 
COISr2H4,  HN03,  which  crystallizes  in  glistening  white  plates, 
readily  soluble  in  water,  but  only  slightly  in  nitric  acid;  also 
the  chloride,  oxalate,  and  phosphate.  But  like  acetamide, 
urea  also  forms  salts  with  metallic  oxides,  especially  with  mer- 
curic oxide,  e.g.  CON2H4,  2HgO;  finally,  it  yields  crystalline 
compounds  with  salts,  e.g.  urea  sodium  chloride,  CON2H4, 
NaCl,  H20  (glistening  prisms),  and  urea  silver  nitrate, 
CON2H4,  AgN03  (rhombic  prisms).  The  precipitate  which 
is  obtained  on  adding  mercuric  nitrate  to  a  neutral  aqueous 
solution  of  urea  has  the  formula  2CON2H4,  Hg(N03)2,  3HgO; 
upon  its  formation  depends  Liebig's  method  for  titrating  urea. 
(See  the  memoirs  of  Pfluger  and  Boliland  on  the  subject,  e.g. 
Pflilger,  Arch.  f.  Phys.  38,  575.) 

Isomeric  with  urea  is  the  amidoxime,  isuret  or  methane 
amidoxime,  NHiCH-NH-OH,  which  is  obtained  from  HCN 
and  NH2OH;  it  crystallizes  in  prisms  (see  p.  188). 

Closely  related  to  carbamide,  NH2»CO'NH2,  is  semicar- 
bazide  or  semihydrocarbazide,  NH2«CO-NH-NH2,  which  is 
the  half  amide  and  half  hydrazide  of  carbonic  acid.  It  may 
be  prepared  from  potassium  cyanate  and  hydrazine  hydrate. 
It  is  a  basic  substance,  melts  at  96°,  and  is  usually  met  with 
in  the  form  of  its  hydrochloride.  It  reacts  with  aldehydes 
and  ketones  in  much  the  same  manner  a^  phenyl-hydrazine, 
yielding  condensation  products  known  as  semicarbazones  : 


H2O  +  C6H6  .  C(CH3)  :  N  -  NH  •  CO  •  NH2, 


UREIDES  285 

which  crystallize  well,  and  have  well-defined  melting-points 
(see  p.  136). 

Alkylated  ureas  are  obtained  by  the  exchange  of  the  amido 
hydrogen  atoms  for  one  or  more  alkyl  radicals. 

They  are  produced  by  Wohler's  synthetical  method,  viz.  by 
the  combination  of  cyanic  acid  with  amines,  or  of  cyanic  esters 
with  ammonia  or  amines,  thus  :  — 

CO-NC2H6  +  NH2.C2H6  =  CO(NH.C2H6)2. 

Also  from  amines  and  carbon  oxy-chloride.  As  examples  may 
be  mentioned: 


Methyl  urea,  OCX^j      a-Diethyl  urea, 
Ethyl  urea,  CO;    ^Diethyl  urea, 


Certain  of  them  closely  resemble  urea;  others,  however,  are 
liquid  and  volatilize  without  decomposition.  Their  constitution 
follows  very  simply  from  the  nature  of  the  products  which 
are  formed  on  hydrolysis;  thus  a-diethyl  urea  breaks  up  into 
carbon  dioxide  and  ethylamine,  and  the  /?-  compound  into 
carbon  dioxide,  ammonia,  and  diethylamine,  in  accordance 
with  the  generalization  enunciated  on  p.  95,  that  alkyl  radi- 
cals which  are  directly  united  to  nitrogen  are  not  separated 
from  it  on  hydrolysis. 

Acyl  Derivatives.  —  By  the  entrance  of  acyl  radicals  into 
urea,  its  acid  derivatives  or  ureides  are  formed.  These  are 
formed  by  the  action  of  acid  chlorides  or  anhydrides  upon 
urea,  or  by  the  action  of  phosphorus  oxy-chloride  upon  the 
salts  of  urea  with  organic  acids.  The  simple  ureides  correspond 
in  many  respects  with  acid  amides  or  anilides,  have  neither 
distinctly  acid  nor  basic  properties,  and  may  be  hydrolysed  to 
the  acid  and  urea  or  its  products  of  decomposition  (p.  283). 
To  this  class  belong  acetyl  urea,  NH2.CO.NH.(X).CH3,  and 
allophanic  acid,  NH2-CO-NH.C02H.  Hydroxy-  monobasic 
acids  also  form  ureides,  not  only  in  virtue  of  their  acidic 
nature,  but  as  alcohol  and  acid  at  the  same  time,  thus:— 


Hydantoic  acid,  nn^--—  2'C02H 


.NH-CH.CH, 

.  NH  -CH2       Dactyl  urea,  CO<         AO 
Hydantom,         OX' 


Hydantoi'n  or  glycolyl  urea  (needles,  neutral)  and  hydantoic 


286  XIII.    CARBONIC  ACID  DERIVATIVES 

acid  or  glycoluric  acid  (prisms),  are  derivatives  of  glycollic  acid  ; 
the  former  on  hydrolysis  yields  hydantoic  acid,  which  in  its 
turn  is  broken  up  into  C02,  NH3,  and  glycocoll.  They  are 
obtained  from  certain  uric  acid  derivatives  (e.g.  allantom)  by 
the  action  of  hydriodic  acid,  and  also  synthetically,  for  in- 
stance, hydantoic  acid  from  glycocoll  and  cyanic  acid.  A 
methyl-hydanto'in,  C3H3(CH3)N202,  results  from  the  partial 
hydrolysis  of  creatinine  (p.  298),  NH  being  here  replaced  by  0. 
Just  as  the  dibasic  acids  —  oxalic,  malonic,  tartronic,  and 
mesoxalic  —  yield  amides  with  ammonia,  so  with  urea  they 
form  compounds  of  an  amidic  nature.  In  such  reactions 
either  two  molecules  of  water  are  eliminated,  so  that  no  car- 
boxyl  radical  remains  in  the  compound,  or  only  one  molecule 
is  eliminated  and  a  carboxyl  group  is  retained.  In  the  former 
case  the  so-called  cyclic  ureides  are  obtained,  and  in  the  latter 
the  ureido-acids,  e.g.  from  oxalic  acid,  parabanic  and  oxaluric 
acids  : 

CO-OH          co^1111'00          co/NH3 

CO-OH  XNH-CO  \NH.CO.OO,H 

Oxalic  acid      Cyclic  ureide  (parabanic  acid)      Ureido-acid  (oxaluric  acid). 

In  an  analogous  manner  the  ureide  barbituric  acid, 
C4H4No03,  is  derived  from  malonic  acid,  the  ureide  dialuric 
acid,  Cf4H4N204,  from  tartronic  acid,  arid  the  ureide  alloxan, 
C4H2N204,  and  ureido-acid  alloxanic  acid,  C4H4N205,  from 
mesoxalic  acid. 

These  are  solid  and,  for  the  most  part,  beautifully  crystal- 
lizing compounds  of  a  normal  amidic  character,  and  therefore 
readily  hydrolysed  to  urea  (or  C02  and  NH3)  and  the  respec- 
tive acid.  The  ureido-acids  may  be  regarded  as  half-hydro- 
lysed  ureides,  and  may  be  prepared  from  the  latter  in  this 
manner.  As  they  contain  a  carboxyl  group,  they  still  possess 
acidic  properties. 

The  constitution  of  the  various  cyclic  ureides  and  ureido- 
acids  follows  in  most  cases  from  the  products  they  yield  on 
hydrolysis,  and  also  from  their  synthetical  methods  of  for- 
mation and  their  relationships  to  one  another. 

Some  of  these  ureides  are  obtained  synthetically  from  urea 
and  the  requisite  acid  often  in  the  presence  of  phosphorus 
oxy-chloride,  e.g.  malonyl  urea  (barbituric  acid), 


from  urea  and  malonic  acid.     Many  can  be  obtained  by  the 


PARABANIC  ACID.   METHYL  URACYL        287 

oxidation  of  various  complex  natural  products,  e.g.  alloxan  or 
parabanic  acid  by  oxidizing  uric  acid  with  nitric  acid. 

Most  of  the  ureides  have  the  character  of  more  or  less 
strong  acids.  Since  this  acid  character  is  not  to  be  explained, 
as  in  the  case  of  the  ureido-acids,  by  the  presence  of  carboxyl 
groups,  one  must  assume  that  it  depends  upon  reasons  similar 
to  those  which  apply  in  the  case  of  cyanic  acid  and  of  suc- 
cinimide,  viz.  that  the  replaceable  hydrogen  atoms  are  imido- 
hydrogen  atoms,  the  acidic  nature  of  which  is  determined  by 
the  adjacent  carbonyl  groups.  This  explains,  for  instance,  why 
parabanic  acid  is  a  strong  dibasic  acid. 

Only  a  few  of  the  more  important  among  these  compounds 
can  be  discussed  here.  The  names  given  to  the  majority  of 
them  have  no  relationship  to  their  constitution,  and  were  as- 
signed to  them  before  the  constitutions  had  been  determined. 

Parabanic    acid,    Oxalyl   urea,   C0<^          •    ,   is  prepared 

by  the  action  of  nitric  acid  upon  uric  acid,  and  crystallizes 
in  needles  or  prisms  soluble  in  water  and  alcohol.  The  salts, 
e.g.  C3HKN203,  C3Ag2N203,  are  unstable,  being  converted  by 
water  into  salts  of  the  monobasic  oxaluric  acid,  NH2-CO» 
NH.CO.C02H,  which  crystallize  well. 


A    methyl  -  parabanic    acid,    CO  •    ,    and   a    di- 

methyl -  parabanic    acid,    the    so-called    "  cholestrophane  ", 
•    ,    are   also  known.      The   former  is   prepared 

by  the  action  of  nitric  acid  upon  methyl-uric  acid,  and  crystal- 
lizes in  prisms,  while  the  latter  is  obtained  from  theine  with 
nitric  acid  or  chlorine  water,  and  also  by  the  methylation  of 
parabanic  acid,  i.e.  from  the  silver  salt  and  methyl  iodide.  It 
crystallizes  in  plates  and  distils  without  decomposition. 

Methyl-  iiracyl,    CO<^;^^>CH,   is  produced   by 

the  action  of  urea  upon  acetoacetic  ester,  water  and  alcohol 
being  eliminated  (Behrend,  A.  229,  1,  and  p.  230).  When  it 
is  treated  with  nitric  acid,  a  nitro-group  enters  the  molecule, 
and  the  methyl-group  is  oxidized  to  carboxyl,  thus  forming 
5-nitro-uracyl-4-carboxylic  acid, 


288  XIII.   CARBONIC  ACID  DERIVATIVES 

This  in  its  turn  can  give  up  carbon  dioxide  and  pass  into 
5-nitro-uracyl, 


which  yields  upon  reduction  with  tin  and  hydrochloric  acid 
5-amino-uracyl  and  isobar  bituric  acid,  5-hydroxy-uracyl, 


This  last  is  oxidized  by  bromine  water  to  isodialuric  acid, 


from  which  uric  acid  may  be  synthesised  by  warming  with 
urea  and  sulphuric  acid  (see  p.  291). 


Barbituric  acid,   Malonyl  urea,  CO<;>CH2,  crys- 


tallizes in  large  colourless  prisms  (+  2H20).  The  hydro- 
gen atoms  of  the  methylene  group  are  reactive  (cf.  ethyl 
malonate),  and  can  be  replaced  by  bromine,  -NOg,  :N-OH, 
metals,  &c.  The  metallic  radicals  in  their  turn  can  be 
replaced  by  alkyl  groups.  The  dimethyl  derivative  when 
hydrolysed  yields  carbon  dioxide,  ammonia,  and  dimethyl- 
malonic  acid,  thus  indicating  that  the  methyl  groups  have 
replaced  the  methylene  hydrogen  atoms.  The  e'so-nitroso 

derivative,  CO<^;^>C:N.OH,  violuric  acid,  can  also 

be  obtained  by  the  action  of  hydroxylamine  on  alloxan,  and 
on  reduction  yields  ammo-barbituric  acid  (uramil),  from  which 
pseudouric  and  uric  acids  have  been  synthesised  (p.  291). 
Diethylbarbituric  acid  (veronal)  is  used  as  a  soporific. 

Dialuric  acid,  Tartronyl  urea,  CO<^;^Q>CH.OH,  crys- 

tallizes in  colourless  needles  or  prisms  which  redden  in  the 
air.  It  is  a  strong  dibasic  acid,  and  on  oxidation  yields  allox- 
an tin. 

Alloxan,  Mesoxalyl  urea,  C0<        '      ^^'  ma^  ^e  Pre~ 


pared  from  uric  acid  by  oxidation  with  cold  HNO3.  It  forms 
large  colourless  glistening  rhombic  prisms  (  +  4H20),  is  readily 
soluble  in  water,  and  has  strongly  acidic  properties.  It  colours 
the  skin  purple-red,  and  with  ferrous  sulphate  solution  pro- 
duces an  indigo-blue  colour.  It  combines  with  NaHSOg,  and 


**       MUREXIDE.      ALLANTOIN  289 

readily  changes  into  alloxantin.  The  corresponding  ureido- 
acid,  alloxanic  acid,  NH2  •  CO  •  NH  .  CO  •  CO  •  C02H,  which 
alloxan  yields  even  with  cold  alkali,  forms  a  radiating  crys- 
talline mass  readily  soluble  in  water.  Methyl-  and  di- 
methyl alloxan  are  also  known,  and  may  be  obtained  by 
the  action  of  nitric  acid  upon  methyl-uric  acid  and  caffeine 
respectively. 

The  diureide  alloxantin,  C8H407N4,  stands  midway  in 
composition  between  tartronyl-  and  mesoxalyl-urea,  by  the 
combination  of  which  it  is  formed.  It  may  also  be  obtained 
by  the  action  of  H2S  on  alloxan,  or  directly  from  uric  acid 
and  HN03.  It  crystallizes  in  small  hard  prisms  (+  3H20), 
which  become  red  in  air  containing  ammonia,  their  solution 
acquiring  a  deep-blue  colour  on  the  addition  of  ferric  chloride 
and  ammonia.  The  tetramethyl  derivative,  amalic  acid, 
C8(CH3)4N407,  is  obtained  by  oxidizing  theine  with  chlorine 
water,  and  forms  colourless  crystals  which  redden  the  skin 
and  whose  solution  is  turned  violet-blue  by  alkali.  Both  these 
compounds  yield,  upon  oxidation,  first  alloxan  or  its  dimethyl 
derivative,  and  then  parabanic  or  dimethyl  -parabanic  acid. 
Alloxantin  probably  has  the  constitution: 


When  heated  with  ammonia  it  is  converted  into  murexide, 
the  acid  ammonium  salt  of  purpuric  acid,  C8H5N605,  which  is 
the  acid  form  of  barbituryl  iminoalloxan  : 

NH.CO 


(J.  pr.  1905,  [ii],  73,  449),  which  is  formed  when  uric  acid  is 
evaporated  with  dilute  nitric  acid,  and  ammonia  added  to  the 
residue;  this  constitutes  the  "murexide  test"  for  uric  acid. 
Murexide  crystallizes  in  four-sided  plates  or  prisms  (+  H20) 
of  a  golden-green  colour,  which  dissolve  to  a  purple-red  solu- 
tion in  water  and  to  a  blue  one  in  potash.  The  free  acid  is 
incapable  of  existence. 

Allantoi'n  is  a  diureide  of  glyoxylic  acid,  of  the  constitution 


. 

ra-co, 

and  is  found  in  the  allantoic  liquid  of  the  cow,  the  urine  of 

(B480) 


290  XIII.   CARBONIC  ACID  DERIVATIVES 

sucking  calves,  &c.     It  forms  glistening  prisms,  and  can  be 
synthesised  from  its  components. 

Biuret,  NH2.CO.NH.(X).NH2,  is  obtained  by  heating  urea 
at  160°: 


2NH2.(X).NH2  =  NH3  +  NH(CO-NH2)2. 

It  crystallizes  in  white  needles  (  -f  H20),  and  is  readily 
soluble  in  water  and  alcohol.  The  alkaline  solution  gives  a 
beautiful  violet-red  coloration  on  the  addition  of  a  little  cupric 
sulphate  —  the  "biuret  reaction".  Biuret  is  also  formed  by 
the  action  of  ammonia  upon  the  allophanic  esters,  crystalline 
compounds  sparingly  soluble  in  water,  which  are  prepared 
from  urea  and  chloro-carbonic  esters,  thus:  — 

CO(NH2)2  +  C1.C02C2H5  =  NH2.CO-NH.CX)2C2H6  +  HC1. 

Allophanic  acid  itself  is  not  known  in  the  free  state,  as  it 
immediately  breaks  up  into  urea  and  carbon  dioxide.  Biuret 
may  be  regarded  as  its  amide. 

The  Purine  Group  (E.  Fischer,  B.  1899,  32,  435;  35,  2564).— 
A  number  of  relatively  complex  cyclic  diureides  derived  from 
1  molecule  of  hydroxy  dibasic  acids  and  2  of  urea  are  known. 
One  of  the  most  important  of  these  is  uric  acid. 

The  parent  substance  of  this  group  of  compounds  is  purine 
(E.  Fischer,  B.  1899,  32,  449). 

Purine  : 


2CH5C.NEK8 


4  9 

is  usually  obtained  from  uric  acid : 
NH-CO 

co  r 

NH.! 

which  reacts  with  phosphorus  oxy-chloride  as  the  tautomeric 
trihydroxy  purine: 

N  =  C-OH 


SYNTHESIS  OF  URIC  ACID  291 


yielding  the  corresponding  trichlorpurine : 
N  =  CC1 


and  this  on  reduction  yields  purine  itself.  It  is  a  colourless 
crystalline  compound,  melts  at  216°,  and  is  both  an  acid  and  a 
base.  It  dissolves  readily  in  water,  and  is  not  easily  oxidized. 
The  atoms  of  the  ring  are  usually  numbered  as  indicated. 

Uric  acid  is  the  keto  form  of  2:Q:8-trihydroxy-purine,  and 
has  the  constitutional  formula: 

NH-CO 
CO   «' 
NH-< 

Uric  acid  and  many  other  compounds  containing  the 
•  NH«CO»  group,  as  tautomeric  substances,  behave  in  certain 
reactions  as  ketonic  compounds  and  in  other  reactions  as  hy- 
droxylic  derivatives,  i.e.  they  exhibit  keto-enolic  tautomerism. 

It  is  a  common  constituent  of  the  urine  of  most  carnivorous 
animals,  whereas  that  of  herbivorous  animals  contains  hippuric 
acid.  It  is  also  found  in  the  blood  and  muscle  juices  of  the 
same  animals,  and  would  appear  to  be  the  oxidation  product 
of  the  complex  nitrogenous  compounds  contained  in  the 
organism.  It  is  also  contained  in  the  excrement  of  birds, 
serpents,  and  insects,  and  in  guano. 

Syntheses. — 1.  By  heating  glycocoll  with  urea  (HorlaczewsU, 
B.  15,  2678). 

2.  By  heating  isodialuric  acid  (p.  288)  with  urea  and  concen- 
trated sulphuric  acid  (R.  Behrend  and  0.  Roosen,  A.  251,  235) : 

NH-CO  NH-CO 

CO    C-OH  +  H2N>CQ  m   00   9/NH\CO  +  2H20. 

NH-C.OH  ^  H^/         NH-C.NH/ 


3.  By  heating  cyano-acetic  acid  with  urea  (Traube,  B.  1891, 
24,  3419;  1900,  33,  3035). 

4.  By  heating  pseudouric  acid  with  hydrochloric  acid  when 
water  is  eliminated  (K  Fischer,  B.  1897,  30,  559): 

NH-CO  NH-CO 

CO    CH.NH-CO-NH2  =  H2O  +  CO    C-NH\C() 

NH-CO  ' 


292  XIII.    CARBONIC   ACID   DERIVATIVES 

The  pseudo  acid  is  obtained  as  the  potassic  salt  by  the 
condensation  of  amino-barbituric  acid  (p.  288)  with  potassic 
cyanate : 

NH.CO  NH-CO 

CO    CH-NH2-f  HCNO  =  CO    CH-NH-CO-NH,,  (Baeyer). 

NH-CO  NH.CO 

It  is  usually  prepared  from  guano  and  the  excrement  of 
serpents,  and  crystallizes  in  small  plates;  is  almost  insoluble 
in  water,  and  quite  insoluble  in  alcohol  or  ether.  Uric  acid 
is  a  weak  dibasic  acid;  its  common  salts  are  the  acid  ones, 
e.g.  C5H303N4K,  a  powder  sparingly  soluble  in  water.  The 
lithium  and  piperazine  salts  are  somewhat  more  soluble,  and 
hence  are  used  in  medicine  for  removing  uric  acid  from  the 
human  system. 

When  the  two  lead  salts  are  treated  with  methyl  iodide, 
methyl-  and  dimethyl  uric  acids  are  obtained,  both  of  which 
also  are  weak  dibasic  acids,  since  they  still  contain  replaceable 
imido-hydrogen  atoms. 

Constitution. — The  constitutional  formula,  given  above,  was 
first  proposed  by  Medicus,  and  afterwards  proved  to  be  correct 
by  E.  Fischer  (A.  215,  253).  The  more  important  arguments 
used  were: — (1)  Uric  acid  yields  alloxan  and  urea  when 
cautiously  oxidized,  this  proving  that  we  have  to  deal  here 
with  a  carbonic  acid  derivative  and  a  carbon  chain,  C«C»C; 
(2)  uric  acid  contains  four  imido  groups,  since,  by  the  intro- 
duction of  four  methyl  groups,  one  after  the  other,  four  mono- 
methyl,  various  di-  and  trimethyl,  and  one  tetramethyl  uric 
acids  are  obtained.  When  the  tetramethyl  acid  is  hydrolysed 
with  concentrated  hydrochloric  acid  all  the  nitrogen  is  elimi- 
nated as  methylamine,  and  thus  each  methyl  group  is  probably 
attached  to  a  nitrogen  atom;  (3)  dimethyluric  acid  yields 
methylalloxan  and  methylurea  on  oxidation. 

Uric  acid  is  usually  recognized  by  its  sparing  solubility,  and 
by  its  giving  the  murexide  test. 

Xan thine,  2:Q-Dihydroxy-purine,  or  the  corresponding  keto 
form: 

NH-CO  NH.CO 

co  C.NH\  CH  C.NH\ 

NH-C-N/C  N_C-N/°H' 

Xanthine  Hypoxantkiue 


DERIVATIVES  293 

may  be  obtained  by  the  reduction  of  uric  acid  with  sodium 
amalgam,  or  by  the  action  of  nitrous  acid  on  guanine  (amino 
hypoxanthine).  It  is  a  white  amorphous  mass,  and  is  both 
basic  and  acidic.  The  lead  salt,  C5H2PbN402,  is  converted 
into  theobromine  by  methyl  iodide.  (Of.  B.  1897,  30,  2235; 
1900,  33,  3035.)  When  oxidized  it  yields  the  same  products 
as  uric  acid. 

Hypoxanthine,  Sarcine,  or  Q-oxy-purine,  is  sparingly  soluble 
in  water  and  closely  resembles  xanthine, 

Theobromine,  3 : 1-Dimethyl-xanthine, 

NH— CO  NMe-00 

CO      C-NMex  CO      C.NMe\ 

NMe  •  C N/  NMe .  C  —  N/      ' 

Theobromine  Caffeine 

occurs  in  the  beans  of  cacao;  it  is  a  crystalline  powder  of 
bitter  taste,  and  is  only  sparingly  soluble  in  water  and  alcohol. 
It  forms  salts  both  as  a  base  and  as  an  acid.  The  silver  salt, 
CrH7AgN402,  when  treated  with  CH3I,  yields  caffeine  or 
theine,  I:3:7-trimethyl-xanthine,  which  occurs  in  tea  (2-4  per 
cent),  coffee,  and  various  plants.  (For  synthesis  from  dimethyl 
urea  and  malonic  acid,  see  Fischer,  B.  1895,  28,  3137;  1899, 
32,  435;  from  cyanoacetic  acid,  1900,  33,  3035.)  It  crystal- 
lizes (+  H20)  in  beautiful  long  glistening  silky  needles  of 
faintly  bitter  taste,  which  are  sparingly  soluble  in  cold  water 
and  alcohol,  and  can  be  sublimed.  The  salts  are  readily  de- 
composed by  water.  Chlorine  oxidizes  it  to  dimethyl  alloxan 
and  monomethyl  urea.  Theophylline,  1 :  3-dimethyl-xanthine, 
also  occurs  in  tea. 

Guanine,  2-amino-Q-oxy-purine,  or  2-amino-hypoxanthine,  and 
adenine,  Q-amino-purine,  both  contain  amino-groups,  and  are 
thus  basic  substances.  Both  compounds,  together  with  xan- 
thine and  hypoxanthine,  are  formed  by  the  decomposition  of 
the  nucleic  acids  and  other  complex  compounds  contained  in 
the  animal  system.  The  constitution  follows  largely  from 
(1)  basic  properties,  (2)  their  conversion  respectively  into 
xanthine  and  hypoxanthine  by  the  aid  of  nitrous  acid,  and 
(3)  from  their  oxidation  products. 

A  summary  of  some  of  the  more  important  ureides  which 
can  be  obtained  from  uric  acid  are  tabulated  here: — 


t-t 


o 

X 


W 


o 

A 


w 


g 

-.8 


v 

o 
o 


V 

o 


si^ill^ljssi 


¥    8 


SULPHUR  DERIVATIVES   OF  CARBONIC  ACID  295 

D.  Sulphur  Derivatives  of  Carbonic  Acid 

In  addition  to  most  of  the  carbonic  acid  derivatives  which 
have  been  described,  there  exist  analogous  compounds  in  which 
the  oxygen  is  wholly  or  partially  replaced  by  sulphur.  Many 
or  these  again  are  unstable  in  the  free  state,  from  the  fact  of 
their  being  too  readily  hydrolysed  to  C02,  COS,  or  CS2,  but 
they  are  known  as  salts,  or  at  least  as  esters.  The  latter  are 
often  not  real  esters,  in  so  far  that  those  which  contain  an 
alkyl  radical  linked  to  sulphur  do  not  yield  the  corresponding 
alcohols  on  hydrolysis,  but  mercaptans,  in  accordance  with  the 
intimate  character  of  this  linking. 

Various  mono-,  di-,  and  tri-thio-derivatives  of  carbonic  acid 
are  known,  according  as  1,  2,  or  3  of  the  oxygen  atoms  are 
replaced  by  sulphur. 

Many  of  the  thio-acids  react  as  tautomeric  substances,  and 
give  rise  to  isomeric  alkyl  derivatives  in  exactly  the  same 
manner  as  hydrocyanic,  cyanic,  and  thiocyanic  acids. 

Thiophosgene,  Thiocarbonyl  chloride,  CSC12.  When  chlorine 
is  allowed  to  act  upon  carbon  disulphide,  there  is  first  formed 
the  compound  CC13'SC1,  which  is  converted  into  thiophosgene 
by  SnCl2.  It  is  a  red,  mobile,  strongly  fuming  liquid  of 
sweetish  taste,  which  attacks  the  mucous  membrane,  and  boils 
at  73°.  In  its  chemical  behaviour  it  closely  resembles  phosgene, 
but  is  much  more  stable  towards  water  than  the  latter,  being 
only  slowly  decomposed  even  by  hot  water.  With  ammonia  it 
yields  ammonium  thiocyanate  and  not  thiocarbamide. 

Thiocarbonic  Acids. — Tri-thiocarbonic  acid  is  made  up  of 
the  constituents  CS2  +  H2S,  so  that  carbon  disulphide  is  its 
thio-anhydride,  while  the  di-thiocarbonic  acids  contain  the 
elements  of  CS2  +  H20  or  of  COS  +  H2S,  and  the  mono- 
acids  those  of  COS  +  H20  or  of  C02  +  H2S.  We  find 
accordingly  that  CS2  combines  with  Na2S  to  CS3Na2,  sodic  tri- 
thiocarbonate,  with  KSC2H5  to  CS(SC2H5)SK,  with  KOC2H5 
(i.e.  an  alcoholic  solution  of  potash)  to  CS(OC2H5)SK,  potas- 
sium xanthate.  In  a  similar  manner  COS  and  CSC12  combine 
with  mercaptides  and  alcoholates. 

Tri-thiocarbonic  acid,  CS3H2,  is  a  brown  oil,  insoluble  in 
water,  and  readily  decomposed,  and  its  ethyl  ester, 
S:C(SC2H5)2,  a  liquid  boiling  at  240°. 

Potassium  xanthate,  S:C<g^H5,  obtained  by  the  action 
of  potassic  ethoxide,  (KOH  +  C2H6OH),  on  carbon  disulphide, 


296  XIII.   CARBONIC  AClt>  DERIVATIVES 

crystallizes  in  beautiful  colourless  needles,  very  readily  soluble 
in  water,  less  so  in  alcohol.  A  solution  of  cupric  sulphate 
throws  down  cupric  xanthate  as  a  yellow  unstable  precipitate, 
hence  the  name.  It  is  employed  in  indigo  printing.  The  free 
xanthic  acid,  or  ethyl  hydrogen  dithiocarbonate,  CS(OC2H5)SH, 
is  an  oil  insoluble  in  water,  and  decomposes  at  so  low  a  tem- 
perature as  25°  into  carbon  disulphide  and  alcohol. 

Thiocarbamic  Acids.— Di-thiocarbamic  acid,  NH2«CS-SH, 
is  formed  as  ammonic  salt  by  the  combination  of  CS2  and  NH3 
in  alcoholic  solution : 

CS2  +  2NH3  =  NH2.CS-SNH4. 

The  free  acid  is  a  reddish  oil  which  easily  decomposes  into 
thiocyanic  acid  and  sulphuretted  hydrogen: 

NH2.CS-SH  =  CSNH  +  SELj. 

Carbon  disulphide  combines  in  an  analogous  manner  with 
primary  amines  to  form  the  aminic  salts  of  alkylated  di-thio- 
carbamic  acids;  thus  ethylamine  yields  ethylamine  ethyl-di- 
thiocarbamate,  C2H5NH.CS.SNH3C2H5.  When  such  salts 
are  heated  above  100°,  H2S  is  evolved  and  a  dialkyl-thio- 
urea  left  behind,  e.g.  diethyl-thio-urea,  CS(NHC2H5)2;  when 
HgCl2  or  AgN03  is  added  to  their  solutions,  the  Hg  or  Ag 
salts  of  the  acids  are  precipitated,  and  these  decompose  on 
boiling  with  water  into  HgS  or  Ag2S  and  the  corresponding 
mustard  oil  (cf.  p.  275): 

2CS(NHC2H5).SAg  =  2CSNC2H5  +  Ag2S  +  H2S. 

Secondary  amines  also  give  rise  to  alkylated  di-thiocarbamic 
acids,  but  the  latter  do  not  yield  mustard  oils. 

Thiocarbamide,  Thio-urea,  sulpho-urea,  S:C(NH2)2  (Reynolds), 
is  the  analogue  of  urea,  and  its  modes  of  formation  are  exactly 
similar  to  those  of  the  latter.  Thus  it  is  formed  from  am- 
monium thiocyanate  just  as  urea  is  from  the  cyanate: 

N:C.SNH4  ^±  CS(NH2)2. 

To  effect  this  molecular  transformation  a  temperature  of 
at  least  130°  is  required,  and  it  is  only  partial,  as  the  reaction 
is  reversible.  At  170°  equilibrium  is  attained  after  45  minutes, 
and  the  mixture  then  contains  only  25  per  cent  of  thiocarba- 
mide  (Reynolds  and  Werner,  P.  1902,  207).  It  may  also  be 


AMIDINES  OF  CARBONIC  ACID  297 

formed  by  the  direct  union  of  sulphuretted  hydrogen  with 
cyanamide:          CN.NH2  +  SH2  =  CS(NH2), 

Thiocarbamide  crystallizes  in  rhombic  six-sided  prisms,  or  — 
if  not  quite  pure—  in  long  silky  needles,  readily  soluble  in 
water  and  alcohol.  M.-pt.  172°.  It  is  easily  hydrolysed  to 
C02,  H2S,  and  2NH3.  HgO  abstracts  H2S  from  it,  with  for- 
mation of  cyanamide.  Cold  permanganate  of  potash  solution 
oxidizes  it  to  urea.  As  a  weak  base  it  forms  salts  with  acids, 
but  at  the  same  time  it  yields  salts  with  HgO  and  other 
metallic  oxides;  it  also  combines  with  salts,  such  as  AgCl, 
PtCl4,  &c.  When  heated  with  alcoholic  potash  to  100°,  it  is 
reconverted  into  (the  potassium  salt  of)  thiocyanic  acid  and 
ammonia. 

Thiocarbamide  gives  rise  to  alkyl  derivatives  (normal  and 
pseudo),  acyl  derivatives,  cyclic  ureides,  &c.,  in  much  the 
same  manner  as  urea  itself. 

E.  Amidines  of  Carbonic  Acid 

Guanidine,  or  Imino-carbamide,  NH:C(NH2)2  (Strecker, 
1861),  may  be  obtained  by  the  oxidation  of  guanine,  also  by 
heating  cyanamide  with  ammonium  iodide,  and  therefore  from 
cyanogen  iodide  and  ammonia: 

=  CN3H5,HI. 


It  is  usually  prepared  by  heating  thio-urea  with  ammonium 
thiocyanate  to  180°-190°,  and  therefore  from  the  thiocyanate 
alone  at  this  temperature  (  Volhard)  : 

CS(NH2)2  +  NH4-CNS  =  C(NHXNH2)2,  CNSH  +  H2S 

Guanidine  isothiocyanate. 

Guanidine  crystallizes  well,  is  readily  soluble  in  water  and 
alcohol,  deliquesces  in  the  air,  and  is  a  sufficiently  strong 
monoacid  base  to  absorb  carbon  dioxide.  Guanidine  car- 
bonate, (CN3H5)2,  H2C03,  crystallizes  beautifully  in  quadratic 
prisms.  The  base  is  readily  hydrolysed,  at  first  to  urea  and 
ammonia,  and  finally  to  ammonia  and  carbon  dioxide. 

By  the  action  of  a  mixture  of  nitric  and  sulphuric  acids 
upon  guanidine  nitrate,  nitro-guanidine,  NH2'C(NH)NH«N02, 
is  obtained,  which  is  readily  reduced  to  amino-guanidine, 
NH2  •  C(NH)NH  •  NH2.  The  latter,  when  boiled  with  alkalis  or 
acids,  breaks  up  into  hydrazine,  N0H4,  ammonia,  and  carbon 


298  XIII.    CARBONIC  ACID  DERIVATIVES 

dioxide,  and  it  yields  with  nitrous  acid  diazo  -  guanidine, 
NH2C(NH)NHN:N-OH,  which  in  its  turn  is  decomposed  by 
alkalis  into  water,  cyanamide,  and  hydrazoic  add,  N3H 
(Curtius,  A.  1900,  314,  339). 

By  the   direct   combination   of   cyanamide   with   glycocoll 
there  is  formed  glycocyamine  : 

NH;C\NH2.CH2.C02H, 
which  readily  loses  water  with  formation  of  glycocyamidine  : 


If,  instead  of  glycocoll,  its  methyl  derivative,  sarcosine,  is  used, 
we  obtain  in  an  analogous  manner  creatine  and  ereatinine 
(Folhard): 


e.CH2.C02H 

Creatine  Creatinine. 

Creatine  is  present  in  the  juice  of  muscle,  and  is  prepared 
from  extract  of  meat  (LieUg).  It  crystallizes  in  neutral 
prisms  (+  H20)  of  a  bitter  taste,  is  moderately  soluble  in 
hot  water,  but  only  slightly  in  alcohol.  When  heated  with 
acids  it  loses  water  and  yields  ereatinine,  which  is  an  invari- 
able constituent  of  urine,  and  which  forms  a  characteristic 
double  salt  with  zinc  chloride,  2C4HrN30  +  ZnCl2.  It  is  a 
strong  base  and  much  more  readily  soluble  than  creatine. 

Creatinine  is  the  methyl  derivative  of  imino-hydantoin,  and 
as  such  yields,  when  carefully  hydrolysed,  ammonia  and  methyl- 
hydantoi'n. 


XIV.  CARBOHYDRATES 

Most  of  the  carbohydrates  which  occur  in  nature  have  been 
known  for  a  long  time.  Cane-sugar  was  found  in  the  sugar- 
beet  by  Marggrafm  1747,  and  dextrose  in  honey  by  Glauber. 
The  transformation  of  starch  into  glucose  (p.  309)  was  first 
observed  by  Kirchoff  in  1811. 

The  name  carbohydrate  was  formerly  applied  to  certain 
substances  which  occur  naturally  in  large  quantities  in  the 
vegetable  and  animal  kingdom,  and  which  could  be  repre- 


CARBOHYDRATES  299 

sented  by  the  general  formula  Cx(H20)y,  where  x  =  6  or  a 
multiple  of  6,  ..^dextrose  ,C6(H20)6  or  C6H  06,  cane-sugar, 
Ci2(H20)n  or  C]2H22On,  and  starch  [Cfl(H20)Jx.  In  addition 
to  these  natural  products,  the  group  at  the  present  time 
includes  a  number  of  compounds  which  have  only  been  ob- 
tained synthetically,  mainly  as  a  result  of  the  researches  of 
E.  Fischer.  The  number  of  carbon  atoms  in  these  varies 
considerably.  Carbohydrates  are  now  known  in  which  the 
hydrogen  and  oxygen  are  not  present  in  the  proportions  of 
2  atoms  of  hydrogen  to  1  of  oxygen,  e.g.  rhamnose,  C6H1205. 

The  carbohydrates  are  usually  divided  into  the  three  fol- 
lowing groups,  according  to  their  relative  complexity: — 

A.  Monosaceharoses. — This  is  the  simplest  group  of  the 
carbohydrates,  and  the  members  are  all  polyhydroxy  alde- 
hydes or  ketones  containing  from  3-9  carbon  atoms.     The 
group  includes  the  common  substances  arabinose,  C5H1005, 
and  the  isomeric  compounds,  C6H1206,  glucose  or  grape-sugf.r, 
and  fructose  or  fruit-sugar.     As  a  rule,  the  compounds  are 
readily  soluble   in   water,   have  a   sweet  taste,  and   do   not 
crystallize  very  readily. 

B.  Bi-   and   Trisaccharoses.  —  These   compounds  may  be 
regarded  as  anhydrides  of  the  monoses,  usually  derived  by 
the  elimination  of   1   molecule  of  water  from  2  mols.  of  a 
monose,  or  of  2  mols.  of  water  from  3  of  a  monose.     It  is  not 
necessary  that  the  2  or  3  molecules  of  monose  should  be  iden- 
tical in  structure,  e.g.  cane-sugar  is  the  anhydride  produced  by 
the  elimination  of  1  mol.  of  water  from  1  mol.  of  glucose  and 
1  of  fructose.     As  anhydro-derivatives  they  are  readily  hydro- 
lysed  by  mineral  acids,  yielding  the  monoses,  from  which  they 
may  be  regarded  as  being  derived. 

Most  of  the  di-  and  trioses  are  soluble  in  water,  crystallize 
very  well,  and  also  possess  a  sweet  taste.  Examples  are  cane- 
sugar,  maltose,  and  milk-sugar. 

C.  Polysaccharoses  or  Polyoses, — This  group  includes  the 
complex  carbohydrates,  such  as  starch,  cellulose,  &c.     They 
may  be  regarded  as  derived  from  the  monoses  by  the  elimi- 
nation of  x  mols.  of  water  from  x  mols.  of  a  monose,  e.g. : 

#C6H1206  -  #H20  =  (C6H1006)X. 

In  conformity  with  such  a  structure  they  are  fairly  readily 
hydrolysed,  yielding  as  the  ultimate  product  a  monose.  As 
a  rule,  they  do  not  dissolve  in  water,  possess  no  sweet  taste, 
and  have  not  been  obtained  in  a  crystalline  form. 


300  XIV.   CARBOHYDRATES 

A.  Monosaeeharoses 

These  are  all  open-chain  polyhydroxy-aldehydes  or  ketones, 


OH  •  CH2  •  CH(OH)  .  CH(OH)  •  CH(OH)  -  OH  :  O  Arabinose, 

OH  •  CH2  •  CH(OH)  •  CH(OH)  •  CH(OH)  •  CO  •  CH2  •  OH    Fructose, 

and  are  divided  into  the  two  main  groups  aldoses  and  ketoses, 
according  to  their  aldehydic  or  ketonic  constitution.  As  a 
rule,  several  hydroxyl  groups  are  present  in  addition  to  the 

aldehydic  'C^     or  ketonic  ^>C:0  group,  and  invariably  one 


of  these  hydroxyl  groups  is  in  the  a-position  with  respect  to 
the  aldehydic  or  ketonic  group. 

The  monoses  are  usually  divided  into  sub-groups,  according 
to  the  number  of  oxygen  atoms  present  in  the  molecule,  e.g.  : 

Trioses,     OH.CH2.CH(OH).CH:0  and  OH.CH2.CO-CH2.OH; 
Tetroses,  OH.CH2.(CH.OH)2.CH:0; 

Pentoses,  OH.CH2.(CH.OH)3.CH:O  and  CH8.(CH.OH)4.CH:0; 
Hexoses,    OH.<JE2.(CH.OH)4.CH:O  and 

OH.CH2.(CH.OH)3.CO-CH2.OH; 
Heptoses,  OH  •  CH2  •  (CH  •  OH)5  •  CH  :  O  ; 
Octoses,     OH.CH2.(CH.OH)6.CH:0; 
Nonoses,    OH-CH2.(CH-OH)7.CH:O. 

As  a  rule,  the  molecule  of  any  single  monose  contains  several 
asymmetric  carbon  atoms,  e.g.  a  hexose,  OH»CH2(CH-OH)4« 
CH:0,  contains  4  asymmetric  carbon  atoms,  and  hence 
should  exist  in  24,  i.e.  sixteen  distinct  optically  active  modi- 
fications, in  addition  to  eight  racemic  forms.  In  most  cases 
all  the  possible  stereo-isomeric  modifications  are  not  known, 
but  the  number  of  such  compounds  known  has  been  largely 
increased  within  recent  years  owing  to  the  brilliant  researches 
of  Emil  Fischer  (B.  1890,  23,  2114;  1894,  27,  3189). 

General  Characteristics  of  Aldoses.  —  As  aldehydes  the 
aldoses  possess  most  of  the  properties  already  described  as 
characteristic  of  fatty  aldehydes. 

They  are  readily  reduced  by  ordinary  alkaline  reducing 
agents,  yielding  polyhydric  alcohols: 


PROPERTIES   OF  ALDOSES  301 

When  oxidized,  they  yield  first  mono-  and  then  dibasic  acids, 
containing  the  same  number  of  carbon  atoms : 

OH.eH2.(CH.OH)4.CH:0  —  OH.CH2.(CH.OH)4.CO.OH 
—  COOH.(CH.OH)4.COOH. 

These  reactions  are  of  considerable  importance  as  direct 
evidence  of  the  aldehydic  nature  of  the  aldoses.  The  first 
stage  of  the  oxidation  is  effected  by  mild  oxidizing  agents, 
such  as  chlorine,  bromine  water,  silver  oxide,  or  ammoniacal 
solutions  of  cupric  salts.  The  last-mentioned  reaction  is  the 
basis  of  the  usual  volumetric  method  for  the  estimation  of 
glucose  and  other  aldoses.  The  aldose  solution  is  added  to  a 
given  volume  of  a  standard  Fehlintfs  solution  (a  solution  con- 
taining cupric  sulphate,  sodic  ammonic  tartrate,  and  sodic 
hydroxide  (p.  253) )  until  the  blue  colour  just  disappears  on 
boiling.  An  even  more  exact  method  is  to  weigh  the  cuprous 
oxide  (as  such,  as  metallic  copper,  or  as  cupric  oxide)  formed 
by  reducing  a  given  volume  of  the  sugar  solution  with  an 
excess  of  Fehling's  solution. 

The  oxidation  to  a  dibasic  acid  requires  somewhat  stronger 
oxidizing  agents,  e.g.  nitric  acid. 

Although  the  aldoses  do  not  combine  directly  with  ammonia 
or  sodic  hydric  sulphite,  they  readily  form  additive  compounds 
with  hydrogen  cyanide : 

OH  •  CH2(CH  •  OH)X  •  CH :  0  +  HCN 

=  OH.CH2(CH.OH)X.CH(OH).CN. 

This  is  an  extremely  important  reaction  as  being  the  basis 
of  a  method  for  passing  from  a  tetrose  to  a  pentose,  or  from  a 
pentose  to  a  hexose  (see  p.  304). 

They  react  normally  with  hydroxylamine,  yielding  oximes, 
more  especially  in  alcoholic  solution,  and  the  oximes  thus 
obtained  may  be  converted  into  a  monose  containing  a  smaller 
number  of  oxygen  atoms  (p.  305). 

They  can  also  react  normally  with  phenyl-hydrazine,  yield- 
ing phenyl-hydrazones,  which,  as  a  rule,  are  sparingly  soluble, 
colourless,  crystalline  compounds  with  definite  melting-points. 
These  are  readily  transformed  back  into  the  aldoses  by  treat- 
ment with  hydrolysing  agents  or  with  benzaldehyde  (A.  1895, 
288,  140).  One  of  the  most  characteristic  properties  of 
monoses  is  the  formation  of  osazones  or  diphenyl-hydrazones. 
This  reaction  may  be  regarded  as  taking  place  in  three  distinct 
stages: — (a)  Formation  of  a  phenyl-hydrazone,  X»CH(OH)« 


304  XIV.   CARBOHYDRATES 

The  ketoses  also  form  metallic  derivatives  and  acetyl  deriva- 
tives. 

Alcoholic  Fermentation  of  Monosaccharoses.— Many  of  the 
natural  products,  e.g.  d-glucose  and  ^-fructose,  are  readily  fer- 
mented by  yeast  (Saccharomyces),  yielding  as  chief  products 
ethyl  alcohol  and  carbon  dioxide  (p.  76).  This  decomposition 
is  undoubtedly  due  to  the  presence  of  an  enzyme,  Buchner's 
zymase,  which  is  contained  in  the  cells  of  the  organism. 
Fischer's  researches  have  shown  that  all  monoses  cannot  be 
fermented,  only  certain  of  those  containing  3  or  a  multiple  of 
3  carbon  atoms.  Even  such  monoses  are  not  all  readily  fer- 
mented, e.g.  ^-glucose  is  fermented  more  readily  than  /-glucose, 
and  the  isomeric  guloses  cannot  be  fermented  by  yeast.  There 
appears  to  be  an  intimate  relationship  between  the  configura- 
tion of  the  monose  molecule  and  of  the  ferment  (enzyme) 
which  is  capable  of  decomposing  it.  Fischer  has  compared 
this  relationship  to  that  of  a  lock  and  its  corresponding  key. 

Conversion  of  an  Aldose  into  an  Isomeric  Ketose. — This  is 
an  interesting  transformation  due  to  E.  Fischer,  and  consists 
in  converting  the  aldose  into  its  osazone,  which  on  hydrolysis 
with  hydrochloric  acid  yields  phenyl-hydrazine  and  a  poly- 
hydroxy-ketonic  aldehyde,  usually  known  as  an  osone.  When 
the  osone  is  reduced,  the  aldehydo-group  is  converted  into  a 
primary  alcoholic  radical,  and  a  hydroxy-ketone  (ketose)  iso- 
meric with  the  original  aldose  is  obtained,  e.g. : 

X-CH(OH).CH:0  —  X.C(:N-NHPh).CH:N.NHPh 

X.CO-CEVOH     -—  X.CO-CH-.O. 

By  this  means  d-glucose  can  be  transformed  into  ^-fructose. 

Synthesis  of  a  Mono  saccharose  from  a  Simpler  Mono- 
saccharose. — The  aldose  is  converted  into  its  cyanhydrin  by- 
means  of  hydrogen  cyanide  (Kiliani): 

X.CH(OH).CH(OH).CH:0  — 

As  this  reaction  involves  the  introduction  of  a  further 
asymmetric  carbon  atom  into  the  molecule,  two  distinct 
optically  active  nitriles  will  be  formed.  As  the  two  com- 
pounds are  not  related  to  one  another  as  object  to  mirror 
image,  they  will  not  be  optical  antipodes,  and  will  not  neces- 
sarily be  formed  in  equal  amount.  The  mixture  of  cyanides  is 
hydrolysed,  the  resulting  hydroxy  acids  converted  into  lactones 


CONVERSION   OF  A  MONOSE  INTO  OTHER  MONOSES      305 

and  then  reduced  with  sodium  amalgam,  when  a  mixture  of 
two  sugars  is  obtained: 

X.CH(OH).CH(OH).CH(OH).C09H 

-^  X.CH.CH(OH).CH(OH).CO 

I 

X.CH(OH).CH(OH).CH(OH).CH:0. 

As  examples  of  this  we  have  : 


/3-Galaheptose. 


By  similar  methods  E.  Fischer  has  succeeded  in  preparing 
octoses  and  nonoses. 

Conversion  of  a  Monosaccharose  into  a  Simpler  Mono- 
saccharose  (Wohl,  B.  1893,  26,  730).—  The  aldose  is  converted 
into  its  oxime,  which  reacts  with  acetic  anhydride,  yielding  an 
acetylated  hydroxy-nitrile,  e.g.: 


—  OH.CH2.[CH.OH]4.CH:N.OH 
—  OAc.CH2.[CH.OAc]4.CN. 

The  nitrile  when  treated  with  ammoniacal  silver  nitrate  solu- 
tion loses  hydrogen  cyanide  and  yields  the  acetyl  derivative  of 
a  lower  monose,  e.g.  : 

0  Ac  •  CH2[CH  •  O  Ac]3  .  CHO, 

from  which  the  monose  itself  is  readily  obtained. 

Another  method  has  been  worked  out  by  Buff  (B.  1898,  31, 
1573;  1902,  35,  2360).  This  consists  in  oxidizing  the  aldose 
to  the  corresponding  monobasic  acid,  and  then  oxidizing  the 
calcic  salt  of  this  with  ferric  acetate  and  hydrogen  peroxide. 
In  this  way  carbonic  acid  is  split  off  and  an  aldose  obtained  : 

OH.CH2.(CH.OH)3.CH.(OH).CO-OH  +  O 

=  OH.CH2(CH.OH)3.CH:0  +  H2C03. 

The  aldose  can  be  isolated  as  its  phenylhydrazone,  and  this 
with  benzaldehyde  yields  the  free  aldose. 
Trioses.  —  When  glycerol  is  oxidized  with  dilute  nitric  acid 

(B480)  U 


306  XIV.   CARBOHYDRATES 

or  other  oxidizing  agents,  a  product  C3H603  is  obtained, 
which  has  been  termed  glycerose.  This  has  been  shown  to 
consist  of  the  ketone,  dihydroxyacetone,  OH-CH2«CO«CH2- 
OH,  with  a  small  amount  of  the  isomeric  aldehyde,  glycer- 
aldehyde,  OH .  CH2 .  CH(OH) .  CH :  0,  and  may  be  regarded 
as  the  simplest  monose.  It  is  a  syrup,  possesses  most  of  the 
characteristic  properties  of  the  monoses,  and  when  warmed 
with  alkalis  undergoes  condensation  and  yields  a  hexose 
(o-acrose)  (p.  312)  which  closely  resembles  fructose. 

Tetroses,  C4H8O4. — A  tetrose,  erythrose,  can  be  obtained 
by  the  oxidation  of  erythritol,  OH  •  CH2[CH  •  OH]2  •  CH2  •  OH, 
with  nitric  acid,  and  is  probably  a  mixture  of  an  aldose  and 
ketose.  Other  tetroses  can  be  obtained  from  the  pentoses  by 
the  general  methods  described  on  p.  305. 

Pentoses. — The  pentoses  are  characterized  by  the  fact  that 
they  yield  furfuraldehyde  or  methyl-furfuraldehyde  upon  pro- 
longed boiling  with  hydrochloric  acid,  water  being  eliminated. 
This  reaction  is  largely  made  use  of  for  their  quantitative  esti- 
mation (B.  1892,  25,  2912;  1898,  30,  2570).  Arabinose  gives 
furfuraldehyde  itself,  while  its  homologue,  rhamnose,  gives 
methyl-furfuraldehyde.  When  warmed  with  hydrochloric  acid 
and  phloroglucinol,  cherry-red  colorations  are  produced.  The 
pentoses  do  not  appear  to  exist  free  in  the  animal  or  vegetable 
kingdom,  but  are  readily  formed  by  the  hydrolysis  of  various 
natural  gummy  carbohydrates. 

J-Arabinose,  C5H1005,  =  OH.CH2.[CH.OH]3.CH:0,  is  pro- 
duced by  boiling  gum-arabic,  cherry  gum,  or  beet-root  chips 
with  dilute  sulphuric  acid,  and  forms  prisms  which  dissolve 
in  water  to  a  dextro-rotatory  solution.  It  combines  with 
hydrogen  cyanide,  and  thus  yields  the  nitriles  of  two  stereo- 
isomeric  hydroxy-caproic  acids,  viz.  Z-mannonic  acid  (Kiliani, 
B.  20,  339,  1233)  and  Z-gluconic  acid  (E.  Fischer).  In  addition 
to  /-arabinose,  a  d-arabinose  and  a  d-l-  or  racemic  arabinose 
are  also  known.  They  are  related  to  one  another  in  exactly 
the  same  manner  as  /-,  d-,  and  r-tartaric  acid.  The  corre- 
sponding alcohol  is  arabitol. 

/-Xylose,  or  Wood-sugar,  is  stereo-isomeric  with  arabinose. 
and  is  prepared  by  boiling  wood-gum,  straw,  and  jute  with 
dilute  sulphuric  acid,  and  is  very  similar  to  arabinose.  (Foi 
its  constitution,  see  B.  24,  537.)  The  corresponding  alcohol  is 
xylitol.  Ribose  (B.  1891,  24,  4214)  and  Lyxose  (B.  1899, 
33,  1798)  are  stereo-isomeric  with  arabinose. 

Rhamnose,  or  Isodulcite,  C6H1206,  =  CH3 .  [CH  •  OH]4 .  CH :  0, 


ALDOHEXOSES  307 

is  obtained  from  several  glucosides,  e.g.  quercitrin  or  xantho- 
rharanin  (yellow  needles,  present  in  French  berries,  Ehamnus 
tinctoria,  &c.),  by  the  action  of  dilute  sulphuric  acid.  It  forms 
colourless  crystals  which  contain  1H20,  melts  at  93°,  and 
when  distilled  with  sulphuric  acid  yields  a-methyl-furfuralde- 
hyde. 

Several  isomerides  of  rhamnose  are  known,  e.g.  fucose  from 
sea-weed,  quinovose,  rhodeose,  and  isorhamnose. 

Hexoses.  —  The  hexoses  constitute  the  most  important 
group,  as  they  contain  all  the  more  common  natural  mono- 
saccharoses,  e.g.  d-glucose,  ^-fructose,  d-galactose,  &c.  These 
occur  in  the  free  state  in  the  juices  of  ripe  fruits,  and 
are  also  found  combined  with  acids  and  other  compounds  in 
the  ether-  or  ester-like  compounds  known  as  glucosides.  They 
are  also  formed  by  the  hydrolysis  of  more  complex  carbo- 
hydrates, e.g.  cane-sugar,  maltose,  milk-sugar,  or  starch,  either 
under  the  influence  of  mineral  acids  or  of  enzymes.  They  are 
sweet  and  for  the  most  part  crystalline  compounds  readily 
soluble  in  water,  sparingly  in  absolute  alcohol,  and  insoluble  in 
ether.  They  possess  the  chemical  properties  of  pentahydroxy- 
aldehydes  and  ketones. 

Aldohexoses.  —  The  common  aldohexoses  have  the  con- 
stitution represented  by  the  formula: 


In  this  formula  the  4  carbon  atoms  contained  within  the 
brackets  are  asymmetric  carbon  atoms,  and  hence  such  a 
compound  should  exist  in  numerous  stereo-isomeric  forms, 
It  can  be  shown  that  in  this  case  the  number  of  optically 
active  isomerides  theoretically  possible  is  sixteen;  of  these 
some  eleven  are  actually  known,  namely: 

Dibasic  Acid,  M.-p.  of 

Aldohexose.         Monobasic  Acid.      COaH[CH-OHVCOaH.        Alcohol.       Osazone. 

d-  &  J-Mannose  d-  &  Z-Mannonic  acid    d-  &  Z-Mannosaccharic  d-  &  Z-M  annitol      206* 

d-&Z-Glucose  d-&Z-Gluconic  acid     d-&Z-Saccharic  d-&Z-Sorbitol        Ibid 

d-&J-Gulose  d-&l-Gnlouic  acid       d-&Z-Saccharic  d-&Z-Sorbitol     157-159* 

d-&Mdose  d-&Mdonic  acid  Idosaccharic         d-&Mditol  193' 

d-&Z-Galactose  d-&Z-Galactonicacid          t-Mucic  i-Dulcitol        193" 

d-Talose  d-Talonic  acid  Talomucic  d-Talitol          193* 

All  of  these  hexoses  have  to  be  represented  by  the  same 
structural  formula,  and  only  differ  as  regards  the  spatial 
arrangements  of  the  various  radicals  within  the  molecule. 
All  are  optically  active  in  solution,  and  the  majority  form 


308  XIV.    CARBOHYDRATES 

pairs  of  optical  antipodes,  e.g.  d-  and  Z-glucose,  which  are 
related  in  exactly  the  same  manner  as  d-  and  Z-tartaric  acids. 
The  members  of  such  a  pair  are  identical  as  regards  their 
ordinary  chemical  and  physical  properties,  with  the  exception 
of  their  effects  on  polarized  light,  and  their  behaviour  towards 
enzymes  or  ferments  generally.  As  a  rule,  one  of  the  two 
compounds  exists  naturally,  e.g.  d-glucose,  and  the  second 
must  be  prepared  by  artificial  means.  The  two  are  able  to 
form  a  racemic  compound,  which  differs  as  regards  its  physical 
properties  from  the  active  components. 

The  determination  of  the  configuration  of  each  aldohexose 
has  been  accomplished  by  E.  Fischer  largely  from  a  study  of 
the  following  points: — (a)  The  relationship  of  the  aldohexose 
to  the  aldopentoses,  e.g.  Z-arabinose  can  be  transformed  into  a 
mixture  of  /-glucose  and  /-mannose,  and  hence  in  all  three 
compounds  the  configuration  of  the  following  part  of  the 
molecule — 

OH  •  CH2  •  CH(OH)  •  CH(OH) .  CH(OH>- 

must  be  identical,  (b)  The  nature  of  the  dibasic  acid  formed 
on  oxidation,  or  of  the  alcohol  formed  on  reduction.  When 
reduced,  ^-galactose  yields  an  inactive  hexahydric  alcohol,  viz. 
i-dulcitol,  and  from  this  it  follows  that  in  the  ^-galactose 
molecule  the  H  and  OH  radicals  must  be  so  spatially  arranged 
that  when  the  -CHiO  group  is  converted  into  a  CH2-OH 
group  a  symmetrical  molecule  is  obtained  (see  formula  below), 
(c)  The  nature  of  the  osazone;  e.g.  ^-glucose  and  d-mannose 
both  give  rise  to  the  same  osazone — d-glucosazone — and  hence 
the  spatial  arrangements  of  the  two  molecules  must  be  identical, 
with  the  exception  of  the  part  •  CH(OH)  •  CH :  0. 

As  the  result  of  such  methods,  the  following  configurations 
have  been  arrived  at  for  some  of  the  commoner  aldohexoses 
(B.  1891,  24,  2683;  1894,  27,  3211):— 

CHO  CHO  CHO  CHO 

HO-C.H  H-C.OH  H-C-OH  H-C-OB 

HO-C.H  H.C-OH  HO-C.H  HO-C.H 

H.C-OH  HO-C.H  H-C-OH  HO-C.H 

H-C-OH  HO-C-H  H-C-OH  H-C-OH 
CH2.OH        CH2OH         CH2OH         CH2OH 

d-Mannose  i-Mannose  cZ-Glucose  <2-Galactose, 


309 

E.  Fischer  has  suggested  the  following  system  of  nomen- 
clature. According  to  the  Geneva  Congress,  the  name  for  glu- 
cose is  hexanepentolal.  Fischer  suggests  that  the  asymmetric 
carbon  atoms  be  numbered  with  respect  to  the  CHO  group, 
and  that  when  the  H  is  to  the  left  and  OH  to  the  right  of  an 
asymmetric  carbon  atom,  it  is  termed  -f  and  the  reverse  — 
Thus: 

e?-Glucose  is  hexanepentolal,  -j \-  -f- 

Z-Glucose  „  1 

c?-Mannose  „  J-  -}- 

rf-Galactose  „  -\ \- 

d-Gulose  „  1 

rf-Idose                    „                +  -  +  - 
d-Talose  „  \- 

d-Glucose,  Grape-sugar  or  dextrose,  C6Hj206  +  H20,  occurs 
together  with  ^-fructose  in  most  sweet  fruits,  in  honey,  also  in 
diabetic  urine.  It  is  prepared  by  the  hydrolysis  of  more  com- 
plex carbohydrates,  e.g.  sucrose  or  starch.  The  usual  method, 
the  hydrolysis  of  starch  with  dilute  sulphuric  acid,  yields 
a  product  which  contains,  in  addition  to  dextrose,  dextrine 
and  unfermentable  substances.  It  crystallizes  from  water  in 
nodular  masses  made  up  of  six-sided  plates  which  melt  at  86°, 
and  from  methyl  alcohol  in  small  anhydrous  prisms  free  from 
water;  m.-pt.  146°.  It  is  dextro-rotatory,  [a]D  =  52-6°,  hence 
the  name  "  dextrose  ". 

A  freshly-prepared  solution  turns  the  plane  of  polarization 
almost  twice  as  much  as  one  which  has  been  kept  or  heated 
to  boiling,  a  phenomenon  which  is  known  as  "bi-,  multi-,  or 
muta-rotation ".  (For  explanation,  cf.  chapter  on  Physical 
Constants  and  Constitution.)  The  strength  of  a  solution  of 
glucose  is  usually  determined  polarimetrically  from  its  specific 
rotatory  power,  or  gravimetrically  by  determining  the  weight 
of  cuprous  oxide  obtained  by  the  reduction  of  Fehling's  solution 
with  a  given  volume  of  the  solution  (cf.  p.  301). 

d-Glucose-plienyl-hydrazone,  C12H18N205,  forms  fine  crys- 
tals which  melt  at  115°.  Another  modification  melts  at 
144°.  d-Phenyl-glucosazone  crystallizes  in  sparingly  soluble 
needles.  The  rotation  produced  by  the  hydrazones  and  osa- 
zones  may  be  the  opposite  of  that  of  the  mother  substance. 
It  is  an  important  point  for  the  recognition  of  the  latter. 
d-Pentacetyl-  glucose,  VJLMQC&jS)*  melts  at  111°. 
d-Glucosone,  CH2(OH).[CH(OH)]3.t50.CHO,  forms  a  syrup 
which  does  not  ferment  with  beer  yeast,  and  which  yields 


310  XIV.    CARBOHYDRATES 

the  osazone  immediately  with  phenyl-hydrazine.  Methyl 
glucoside, 

OH.CH2.CH(OH).CH.(CH.OH)2.CH.OCH3, 

exists  in  two  stereo-isomeric  modifications,  melting  at  165° 
and  107°.  /-Glucose  resembles  e£-glucose  closely,  excepting 
that  it  turns  the  plane  of  polarization  as  strongly  to  the  left 
as  the  latter  does  to  the  right.  i-Glucose,  from  i-gluconic 
acid,  is  a  colourless  syrup.  The  osazone,  i-glucosazone,  melts 
at  216°,  and,  apart  from  rotatory  power,  is  deceptively  like 
the  d-  and  £-osazones. 

Constitution  of  ^-Glucose, — Its  constitution  as  a  penta- 
bydroxy  aldehyde  follows  from  the  formation  of  a  pentacetyl 
derivative,  and  from  its  oxidation  first  to  a  monobasic  acid 
(gluconic  acid)  and  then  to  a  dibasic  acid  (saccharic  acid), 
both  of  which  contain  the  same  number  of  carbon  atoms  as 
glucose.  A  proof  both  of  its  aldehydic  nature  and  of  the 
normal  structure  was  afforded  by  Kiliani  (B.  1886,  19,  767), 
who  prepared  the  cyanhydrin,  hydrolysed  this  to  the  hexa- 
hydroxy-carboxylic  acid,  and,  by  reducing  this  with  hydriodic 
acid  and  phosphorus,  obtained  w-heptylic  acid : 

OH.CH2.(CH.OH)4.CH:O  —  OH.CH2.(CH.OH)4-CH(OH).CN 
CH3.(CH2)5.C02H  —  OH.CH2.(CH.OH)6.C02H  — 

a  product  which  could  not  have  been  produced  if  the  glucose 
had  possessed  either  a  ketonic  or  an  iso-chain  (cf.  Fructose). 
(For  configuration,  see  p.  308.) 

rf-Mannose  is  stereo-isomeric  with  d-glucose,  and  is  formed 
together  with  e£-fructose  by  the  cautious  oxidation  of  mannitol, 
also  by  boiling  the  reserve  cellulose  of  the  seed  of  the  Brazil- 
nut  with  dilute  hydrochloric  acid,  and  by  reducing  mannonic 
acid  lactone  with  sodium  amalgam.  It  forms  a  colourless 
amorphous  mass  readily  soluble  in  water,  is  dextro-rotatory, 
[alp  =  +14 *36°,  and  yields  the  same  osazone  as  ^-glucose. 
When  treated  with  sodium  amalgam  it  passes  readily  into 
d-mannitol.  The  hydrazone  melts  at  195°,  and  is  sparingly 
soluble  in  water.  z-Mannose  forms  a  colourless  syrup.  The 
osazone  is  identical  with  that  from  t-fructose.  /-Mannose  is 
not  so  readily  fermented  as  the  ^-isomeride. 

d-Galactose  is  formed  together  with  ^-glucose  by  the  hydro- 
lysis of  milk-sugar  with  dilute  acid,  and  also  from  certain 
gums.  It  crystallizes  in  slender  needles,  melts  at  166°,  is 


KETOHEXOSES  311 

dextro-rotatory,  [a]D  =  +80-3°,  and  readily  fermented.  Its 
pentacetyl  derivative  melts  at  143°,  a-methylgalactoside  at 
111°,  and  the  stereo-isomeric  /^-compound  at  173°-175°. 

Talose  is  a  syrup.  The  phenyl-hydrazone  is  very  readily 
soluble  in  water  (difference  from  galactose). 

Ketohexoses,  OH.CH2.[CH.OH]3.CO.CH2.OH,  are  struc- 
turally isomeric  with  the  aldohexoses.  As  ketones  they  can- 
not be  oxidized  to  acids  containing  the  same  number  of  carbon 
atoms  (cf,  pp.  68  and  303).  The  formula  contains  3  asym- 
metric carbon  atoms,  and  hence  numerous  stereo-isomerides 
are  theoretically  possible. 

^-Fructose,  Fruit-sugar  or  Icevulose,  C6H1206,  is  almost  invari- 
ably found  along  with  d-glucose  in  the  juice  of  sweet  fruits 
and  also,  together  with  the  latter,  in  honey.  It  is  formed 
along  with  d-glucose  by  the  inversion  of  cane -sugar,  and 
together  with  d-mannose  by  the  cautious  oxidation  of  d-man- 
nitol;  also  from  d-phenyl-glucosazone,  and  therefore  indirectly 
from  d-glucose.  It  is  most  easily  prepared  by  heating  inulin 
(p.  319)  with  very  dilute  acid  (B.  23,  2084);  is  somewhat  diffi- 
cult to  obtain  crystalline,  and  then  forms  hard,  anhydrous, 
rhombic  crystals  melting  at  95°.  It  is  laevo-rotatory,  although 
belonging  genetically  to  the  ^-series.  Its  power  of  rotation  is 
almost  double  that  of  /-glucose.  It  may  be  separated  from 
^-glucose  by  means  of  its  sparingly  soluble  lime  compound. 

Its  close  relationship  to  ^-glucose  is  shown  by  the  fact  that 
it  yields  the  same  osazone,  and  on  reduction  yields  a  mixture 
of  d-mannitol  and  d-sorbitol.  On  oxidation  it  yields  glycollic 
and  tartaric  acids,  or  glycollic  and  trihydroxy-butyric  acids. 
With  methyl-phenyl-hydrazine  it  yields  a  colourless  osazone. 
It  is  fermentable,  but  not  so  readily  as  d-glucose. 

I- Fructose  closely  resembles  d- fructose,  but  is  dextro- 
rotatory, and  as  it  is  not  readily  fermented,  can  easily  be 
obtained  from  i-fmctose,  which  is  a  syrup. 

Constitution  of  ^-Fructose. — The  general  properties  point  to 
its  ketonic  structure,  and  this  was  further  proved  by  Kiliani, 
who  hydrolysed  the  cyanhydrin,  and  then  reduced  the  hydroxy- 
acid  thus  obtained  with  hydriodic  acid  and  phosphorus,  and 
obtained  methvl-butyl-acetic  acid: 

/OH 
OH.CH8.(CH.OH)3.CO.CH2.OH  —  OH.CH2.(CH.OH)8.C<-CN 

I  NO-tlj»Uli 


312  XIV.  CARBOHYDRATES 

Its  configuration  as  Jiexanepentol-2-one f-  +  follows  from 

its  close  relationship  to  ^-glucose. 

CHO  CH2-OH 

d-Glucose,     fl-C-OH  rf-Fructose,          CO 

HO-C-H  HO-C-H 
H-C.OH  H.C-OH 

H.C-OH  H.C.OH 

CH2-OH  CH2OH, 

since  both  yield  the  same  osazone. 

Other  stereo-isomeric  ketohexoses  are  d-tagatose,  obtained 
by  the  action  of  potassic  hydroxide  solution  on  d-galactose. 
It  melts  at  124°,  and  yields  the  same  osazone  as  d-galactose. 
d-Sorbose,  obtained  by  oxidizing  d-sorbitol;  and  /-sorbose, 
obtained  as  a  by-product  in  the  preparation  of  d-tagatose. 

Synthesis  of  Hexoses. — 0.  Loew  obtained,  by  the  action  of 
lime-water  on  formaldehyde,  a  substance  which  he  termed 
formose,  C6H1206,  but  which  has  since  been  shown  to  be  a 
mixture  of  hexoses  containing  a-acrose.  Butleroff  has  ob- 
tained a  similar  product  from  trioxymethylene.  Fischer  and 
Tafel  (B.  1887,  20,  1093,  3384;  1889,  22,  97)  obtained  a 
mixture  of  sugars  by  the  action  of  baryta  water  on  glycerose 
(p.  306).  Among  these  sugars  was  a-acrose,  which  is  the 
starting-point  for  the  synthesis  of  most  other  hexoses.  The 
a-acrose  is  converted  into  its  osazone;  this  is  hydrolysed  to 
the  osone,  and  then  reduced  to  the  ketose,  when  d-Z-fructose 
is  obtained.  According  to  Neuberg  (B.  1902,  35,  2626)  the 
original  a-acrose  is  d-Z-fructose,  since  it  reacts  with  methyl- 
phenyl-hydrazine,  yielding  methyl-phenyl-fructosazone.  The 
scheme  (p.  313)  gives  a  rtsumb  of  the  steps  involved  in  the 
synthesis  of  the  other  hexoses  from  a-acrose. 

The  action  of  alkalis  on  hexoses  has  been  studied  by  Lobry 
de  Bruyn  (B.  28,  3078),  who  has  shown  that  glucose,  mannose, 
and  fructose  are  partially  transformed  into  each  other  under 
the  influence  of  dilute  alkalis: 

Glucose  ^=±  fructose  ^z±  mannose. 

Fructose  appears  to  be  formed  as  an  intermediate  product 
in  the  conversion  of  glucose  into  mannose.  The  transfor- 
mation is  only  partial,  and  is  accompanied  by  a  change  in 
rotatory  power 


SYNTHESIS  OF  HEXOSES 


311 


-3   " 

S      X 


I  „ 

jli= 


—  §  *o_ 


"""3 

2 


if 

I 


31 4  XIV.   CARBOHYDRATES 

B.  Di-  and  Trisaeeharoses 

This  group  comprises  those  carbohydrates  which  may  be 
regarded  as  derived  from  2  or  3  molecules  of  a  monose  by 
the  elimination  of  1  or  2  mols.  of  water  respectively.  As 
such  anhydrides,  they  are  all  readily  hydrolysed  when  boiled 
with  dilute  acids,  yielding  monoses,  usually  hexoses.  Thus 
cane-sugar  yields  a  mixture  of  d-glucose  and  d-fructose;  mal- 
tose yields  ^-glucose  only;  milk-sugar  yields  ^-glucose  and 
d-galactose : 

C12H22On  +  H20  =  2C6H1206. 

Raffinose  or  melitriose  is  a  type  of  a  trisaccharose,  and  on 
hydrolysis  yields  melibiose  and  d-fructose.  The  hydrolysis  in 
most  of  these  cases  can  not  only  be  effected  by  means  of  acids, 
but  also  by  means  of  enzymes,  e.g.  diastase  and  invertase 
hydrolyse  cane-sugar,  maltase  malt-sugar,  &c. 

The  disaccharoses  are  thus  ethereal  anhydrides  of  the  hex- 
oses, e.g.  cane-sugar  is  d-glucose-d-fructose  anhydride,  and  malt- 
sugar  d-glucose  anhydride,  &c.  In  this  anhydride  formation 
8  of  the  original  10  OH  groups  have  remained  intact,  as  the 
bioses  readily  yield  octacetyl  derivatives: 

2C6HrO(OH)5  =  [C6H70(OH)4]20  +  H2O. 

The  compounds  possess  for  the  most  part  a  sweet  taste,  and 
crystallize  more  readily  and  are  more  stable  than  the  monoses, 
but  resemble  the  latter  in  solubility.  They  are  not  directly 
fermentable,  but  are  readily  fermented  after  hydrolysis  to 
monoses.  All  those  which  occur  naturally  are  optically 
active.  Cane-sugar  does  not  reduce  Fehling's  solution,  but 
milk-  and  malt-sugars  do. 

Cane-sugar  or  Sucrose,  SaccharoUose,  C12H?2On>  occurs  in  red 
beet  (Beta),  in  the  sugar-cane  (Saccharum),  in  the  sugar-maple 
(Sorghum),  and  in  many  other  plants,  chiefly  in  the  stem. 

Preparation. — (a)  From  sugar-cane  by  expressing  .the  juice 
and  evaporating  it  until  crystallization  begins.  (&)  From 
sugar-beet  by  a  systematic  extraction  of  the  pulp  with  water, 
e.g.  by  the  "diffusion  process".  The  impure  juice  is  then 
treated  with  lime  ("defecation"),  the  excess  of  the  latter 
thrown  down  by  carbon  dioxide  ("saturation"),  and  the  syrup 
filtered  through  animal  charcoal,  and  evaporated  in  vacuo  to 
crystallization.  From  the  mother-liquid  of  molasses  the  crys- 
tallizable  sugar  still  present  can  be  obtained  as  the  sparingly 


CANE-SUGAR,   MILK-SUGAR,   AND  MALTOSE  315 

soluble  strontium  saccharate,  C12H22On,  SrO,  which  is  then 
suspended  in  water  and  decomposed  by  carbon  dioxide  ("de- 
sugarizing  of  molasses"), 

Cane-sugar  crystallizes  in  large  monoclinic  prisms,  as  is  well 
seen  in  sugar-candy,  and  is  soluble  in  one-third  of  its  weight  of 
water.  It  is  not  turned  brown  when  heated  with  potash,  and 
yields  saccharates  with  lime  and  strontia,  e.g.  C12H.2Z0U  +  CaO 
+  2H20;  C12H22On  +  2CaO;  C12HW0U  +  3CaO.  Concen- 
trated sulphuric  acid  produces  charring  (difference  from 
^-glucose).  Cane-sugar  melts  at  160°,  and  remains  in  the 
amorphous  condition  for  some  time  after  cooling  (barley- 
sugar);  when  heated  more  strongly,  it  becomes  brown  from 
the  formation  of  caramel  or  sugar  dye,  and  finally  chars. 

The  percentage  of  sugar  in  a  solution  of  unknown  strength 
can  be  determined  from  the  specific  rotatory  power  ([a]2D  = 
4-66-5°)  by  measuring  the  angle  (a)  through  which  the  plane 
of  polarization  is  turned  when  a  ray  of  polarized  light  is  passed 
through  a  layer  of  the  solution  of  known  length  (cf.  p.  309). 
This  is  known  as  saccharimetry. 

It  is  readily  hydrolysed  by  acids,  and  this  process  is  com- 
monly spoken  of  as  the  inversion  of  cane-sugar,  and  the  pro- 
duct as  invert  sugar.  These  names  are  due  to  the  fact  that 
the  hydrolysis  is  accompanied  by  a  change  in  the  optical 
activity  of  the  solution.  The  solution  of  cane-sugar  is  dextro- 
rotatory, but  after  hydrolysis  (or  inversion)  it  becomes  laevo- 
rotatory,  as  ^-fructose  is  more  strongly  laevo-  than  d-glucose  is 
dextro-rotatory. 

Sucrose  itself  does  not  reduce  Fehling's  solution,  but  after 
inversion  readily  reduces.  This  would  indicate  that  in  the 
anhydride  formation  the  aldehydic  group  of  ^-glucose  and  the 
ketonic  group  of  ^fructose  have  been  destroyed.  The  con- 
stitutional formula  suggested  by  E.  Fischer  (B.  1893,  26, 
2405)  is: 


This  formula  readily  accounts  (a)  for  the  formation  of  an 
-octacetyl  derivative  (m.-pt.  67°);  (b)  for  the  absence  of  all 
reducing  properties;  (c)  for  the  readiness  with  which  it  can 
be  hydrolysed,  since  the  two  hexose  molecules  are  united  by 
means  oi  an  atom  of  oxygen;  (d)  for  the  non-formation  of  a 
hydrazdrie. 
Milk-sugar  or  Lactose,  Lactobiose,  C12H22On  +  H20,  occurs 


316  XIV.    CARBOHYDRATES 

in  milk,  and  only  occasionally  in  the  vegetable  kingdom.  It  is 
obtained  by  evaporating  sweet  whey.  It  crystallizes  in  hard 
rhombic  prisms,  and  is  much  less  sweet  than  cane-sugar,  and 
also  much  less  soluble  in  water.  It  is  converted  into  "  lacto- 
caramel"  at  180°.  It  shows  muta-rotation  (p.  309),  and  reduces 
Fehling's  solution. 

Maltose  or  Malt-sugar,  Maltobiose,  C]2H22On  -f  H20,  is 
formed  by  the  action  of  diastase  upon  starch  during  the  ger- 
mination of  cereals  (preparation  of  malt).  It  forms  a  hard 
white  crystalline  mass,  very  similar  to  grape-sugar,  and 
strongly  dextro-rotatory.  It  reduces  Fehling's  solution,  but 
only  to  about  two-thirds  the  extent  to  which  ^-glucose  does. 

Lactose  and  maltose  resemble  one  another  very  closely,  and 
are  probably  stereo-isomeric.  Since  they  both  possess  reduc- 
ing properties,  yield  hydrazones,  cyanhydrins,  and  can  be 
oxidized  to  monobasic  acids  containing  the  same  number  of 
carbon  atoms,  it  is  obvious  that  they  must  contain  an  alde- 
hydo- group,  and  the  following  structural  formula  has  been 
given  to  both  by  E.  Fischer  (B.  1893,  26,  2405):— 

OH.CH2.CH(OH).CH.(CH.OH)2.CH.O.CH2.(CH.OH)4.CH:0 

Raffinose  or  Melitriose,  C18H32O16  -f  5  !!./),  is  found  in  the 
sugar-beet,  and  therefore  in  molasses,  in  the  manna  of  the 
eucalyptus,  and  in  cotton-seed  cake,  &c.  It  is  very  like  cane- 
sugar  but  tasteless,  is  strongly  dextro-rotatory,  and  does  not 
i'educe  Fehling's  solution.  When  inverted,  it  yields  in  the  first 
instance  d-fructose  and  "melibiose",  the  latter  then  breaking 
up  into  galactose  and  d-glucose.  (For  its  constitution,  see 
B.  1889,  22,  3118;  also  A.  232,  169.) 

Isomaltose  is  a  biose  obtained  synthetically  by  Fischer 
(B.  1895,  28,  3024)  by  the  condensing  action  of  hydrochloric 
acid  on  glucose.  It  is  non-fermentable. 

C.  Polysaccharoses 

The  empirical  formula  of  the  members  of  this  series  is 
CgHjQpg,  but  they  all  possess  a  much  higher  molecular  weight, 
e.g.  (CgHjoO,^.  They  are  for  the  most  part  .amorphous  and 
tasteless,  insoluble  in  alcohol  and  ether;  a  few  are  soluble  in 
cold  water,  but  the  majority  not;  thus  cellulose  is  insoluble 
and  also  mucilage,  the  latter  merely  swelling  up  with  water, 
while  starch  forms  a  jelly  with  hot  water.  When  boiled  with 


CELLULOSE  317 

dilute  acids  or  subjected  to  the  action  of  enzymes,  they  are 
hydrolysed  to  mono-  or  di-saccharoses,  generally  to  hexoses 
e.g.  rC6H10(X  +  II  0  =  C6H1?06.  The  formation  of  pentoses 
is  frequently  to  be  noticed  in  this  decomposition. 

Like  the  foregoing  compounds,  therefore,  the  members  of 
this  group  are  to  be  regarded  as  the  anhydrides  of  hexoses  or 
pentoses.  Consequently  they  still  possess  an  alcoholic  character 
and  yield  acetic  and  nitric  esters,  &c.  Most  of  them  are  opti- 
cally active.  With  dilute  nitric  acid  they  yield  the  same  oxida- 
tion products  as  are  obtained  from  the  corresponding  hexoses 
or  pentoses,  and  iodine  frequently  gives  characteristic  colora- 
tions. 

Cellulose,  (CgH^O^,  is  widely  distributed  in  nature  as  the 
membrane  of  plant  cells;  cotton,  elder  pith,  wood,  &c.,  consist 
of  cellulose  in  a  more  or  less  pure  state.  It  can  be  prepared 
by  extracting  cotton-wool  or  Swedish  filter-paper  with  caustic 
potash,  hydrochloric  acid,  water,  alcohol,  and  ether  succes- 
sively, or  by  treating  pine  wood  with  sulphuric  and  a  little 
nitric  acid.  It  forms  a  white  amorphous  powder,  insoluble  in 
the  ordinary  reagents,  but  soluble  in  an  aminoniacal  solution 
of  cupric  oxide,  from  which  it  is  again  thrown  down  by  acids. 

When  boiled  with  dilute  sulphuric  acid,  it  yields  dextrine 
and  d-glucose,  while  the  concentrated  acid  converts  it  first 
into  amyloid,  an  amorphous  mass  which  is  turned  blue  by 
iodine,  and  finally  into  dextrine.  Parchment  paper  is  simply 
unglazed  paper  which  has  been  transformed  superficially  into 
amyloid  by  sulphuric  acid. 

Many  cellulose  derivatives  are  compounds  of  commercial 
importance.  The  nitric  esters,  so  called  mtro-celluloses,  are 
used  for  a  variety  of  purposes,  and  are  usually  prepared  by 
the  action  of  a  mixture  of  nitric  and  sulphuric  acids  on  the 
carbohydrate.  The  nature  of  the  product  depends  largely  on 
the  concentration  of  the  acid  mixture  and  upon  the  tempera- 
ture. In  order  to  render  the  products  stable,  it  is  necessary  to 
remove  all  traces  of  free  acid.  Collodion,  a  tetranitrate,  is 
soluble  in  a  mixture  of  alcohol  and  ether  (1:7),  and  the  solu- 
tion is  largely  used  for  coating  materials  and  rendering  them 
air-tight.  It  is  also  used  for  the  manufacture  of  artificial  silk 
and  in  photography.  When  mixed  with  camphor  (various 
other  substitutes,  such  as  phenolic  esters,  are  now  used)  it 
forms  ordinary  celluloid.  Gun-cotton,  pyroxiline,  is  probably 
a  hexanitrate;  in  appearance  it  resembles  cotton  wool,  but  is 
not  so  soft.  It  burns  readily  and  explodes  when  struck  or 


318  XIV.   CARBOHYDRATES 

strongly  heated.  It  is  largely  used  for  making  smokeless 
powders,  and  is  often  met  with  in  the  form  of  compressed 
cakes. 

Practically  all  artificial  silks  are  cellulose  derivatives.  The 
oldest  method  (Chardonnel)  consisted  in  dissolving  cellulose 
nitrates  in  a  mixture  of  alcohol  and  ether  (3:2),  and  forcing 
the  solution  under  pressure  from  a  copper  vessel  through  small 
capillary  tubes  into  water.  The  thread  thus  obtained  was 
stretched  to  about  the  thickness  of  natural  silk,  and  as  it  be- 
came hard  was  wound,  dried,  and  denitrated  by  treatment 
with  a  reducing  agent,  such  as  ammonium  sulphide  or  cuprous 
chloride  and  hydrochloric  acid. 

Other  methods  which  are  now  adopted  consist  in  (a)  the  use 
of  cellulose  acetates  obtained  by  the  action  of  acetyl  chloride 
and  zinc  acetate  or  quinoline,  or  of  acetic  anhydride  and  a 
mineral  acid  on  cellulose.  The  solution  of  the  acetate  is 
squirted  into  alcohol  through  small  holes,  (b)  The  use  of  a 
solution  of  cellulose  in  ammoniacal  cupric  oxide,  and  forcing 
the  solution  through  small  holes  into  dilute  acid  (Thiele  silk), 
(c)  Use  of  viscose.  Artificial,  human,  and  horse  hair  are  manu- 
factured by  similar  methods.  The  artificial  silks  are  used  for 
the  manufacture  of  fabrics,  and  also  for  insulating  metallic 
wires.  Viscose  (Cross  and  Bevari)  is  the  sodium  salt  of  cellu- 
lose xanthate.  Cotton  fibre  is  allowed  to  swell  by  treatment 
with  sodium  hydroxide  solution,  and  is  then  shaken  with  car- 
bon disulphide.  Its  solution  in  water  forms  a  gelatinous  mass 
which  can  be  moulded.  When  exposed  to  the  air  it  shrinks 
and  hardens  to  a  horn-like  mass.  It  is  used  as  a  substitute 
for  glue,  celluloid,  horn,  ivory,  &c.  When  used  for  the  manu- 
facture of  artificial  silk  it  is  necessary  to  purify  it;  this  is  done 
by  acidifying  with  a  weak  acid  (acetic  or  lactic),  precipitating 
with  alcohol  or  brine,  and  washing. 

Viscoid  is  a  mixture  of  viscose  with  clay  or  zinc  oxide,  and 
sets  to  an  extremely  hard  mass. 

Starch  or  Amylum,  (C6H1006)r,  is  present  in  all  assimilating 
plants,  being  built  up  by  the  chlorophyll  granules  from  the 
carbon  dioxide  absorbed,  and  is  found  especially  in  the  nutri- 
ment reservoirs  of  the  plants,  e.g.  in  the  grains  of  cereals,  in 
perennial  roots,  potatoes,  &c.  It  is  converted  into  sugar 
during  the  transference  of  the  sap.  It  forms  a  white  velvety 
hygroscopic  powder  which  consists  of  round  or  elongated 
granules  built  up  of  concentric  layers,  and  insoluble  in  cold 
water.  The  interior  of  these  granules  consists  of  "  granulose  " 


GUMS  AND  DEXTRINES  319 

and  their  husk  probably  of  cellulose.  When  they  are  wanned 
with  water,  the  latter  is  broken  open  and  the  granulose  dis- 
solves; if  the  solution  is  moderately  dilute,  it  can  be  filtered 
and  a  clear  solution  obtained,  from  which  alcohol  precipitates 
"  soluble  starch  ".  Both  the  granules  of  starch  and  its  jelly  are 
coloured  an  intense  blue  by  iodine  and  bright  yellow  by  bro- 
mine, from  the  formation  of  loose  additive  compounds,  "iodide 
and  bromide  of  starch  ".  The  colour  of  the  iodide  of  starch 
vanishes  on  heating,  but  reappears  on  cooling.  Ordinary  air- 
dried  starch  contains  some  10-20  per  cent  of  water,  which  can 
be  removed  by  heating  to  105°. 

The  so-called  "  soluble  starch  "  is  formed  (a)  when  starch  is 
heated  with  glycerol,  (b)  when  starch  is  boiled  with  water  con- 
taining sulphuric  acid,  (c)  by  the  action  of  diastase  or  starch. 
Further  treatment  with  acid  converts  it  into  dextrine  and 
^-glucose,  and  with  diastase  into  dextrine  and  maltose  and 
isomaltose  (B.  1893,  26,  2533).  Warming  with  very  little 
dilute  nitric  acid  to  110°  yields  dextrine. 

Lichenin,  or  Moss  starch,  present  in  many  lichens,  e.g.  in 
Iceland  moss  (Cetraria  islandica),  is  coloured  a  dirty  blue  by 
iodine;  and  inulin,  present  in  the  roots  of  the  dahlia  and 
many  composites  (Inula  Helenium),  is  coloured  yellow  by 
iodine  and  converted  into  ^-fructose  when  boiled  with  water. 

Glycogen,  or  Animal  starch,  Liver  starch,  is  present,  e.g.  in 
the  livers  of  the  mammalia.  It  is  a  colourless  amorphous 
powder  which  is  turned  wine-red  by  iodine;  after  the  death 
of  the  animal  it  rapidly  changes  into  d-glucose,  the  same 
conversion  being  effected  by  boiling  with  dilute  acids,  while 
enzymes  transform  it  into  maltose. 

Dextrine,  or  Starch  gum,  is  a  comprehensive  name  applied  to 
intermediate  products  obtained  in  the  transformation  of  starch 
into  maltose  and  d-glucose.  It  may  be  prepared  (a)  by  heating 
starch  either  alone  or  with  a  little  nitric  acid,  (b)  together  with 
d-glucose  by  boiling  starch  with  dilute  sulphuric  acid,  and  (c) 
together  with  maltose  by  the  action  of  diastase  on  starch.  The 
dextrines  are  soluble  in  water,  and  are  precipitated  by  alcohol. 
They  are  often  named  according  to  their  reaction  with  iodine, 
e.g.  amylo-dextrine  blue,  erythro-dextrine  red,  and  achroo- 
dextrine  no  colour.  They  do  not  reduce  Fehling's  solution 
even  when  warmed,  and  are  not  directly  fermentable  by  yeast 
but  only  after  the  prolonged  action  of  diastase,  glucose  being 
formed  as  an  intermediate  product. 

Synthesis  of  Sugars. — The  sugars  are  extremely  important 


320  XIV.    CARBOHYDRATES 

from  the  point  of  view  of  plant  physiology.  The  plant  ab- 
sorbs carbon  dioxide  and  water,  and  with  the  aid  of  sunlight 
is  capable,  in  the  presence  of  chlorophyll,  of  transforming  these 
into  glucose  and  even  more  complex  carbohydrates.  Various 
speculations  have  been  made  with  regard  to  the  manner  in 
which  these  complex  compounds  Are  formed.  Baeyer  has  sug- 
gested that  the  carbon  dioxide  is  first  reduced  to  formaldehyde, 
and  this  then  polymerizes  as  in  Loew's  experiments,  yielding 
carbohydrates, 


C02  —  H.C          ->  (H2C:0)6  =  C6H12O6. 

For  many  years  the  important  link  in  this  chain,  viz.  the 
reduction  of  carbon  dioxide  to  formaldehyde,  was  missing; 
the  reaction  could  not  be  accomplished  in  the  laboratory. 
Fenton  has  recently  shown  (J.  C.  S.  1907,  91,  687)  that  when 
carbon  dioxide  is  passed  into  water  in  which  sticks  of  mag- 
nesium are  immersed,  a  small  amount  of  the  gas  is  reduced  to 
formaldehyde,  especially  in  the  presence  of  ammonia  or  phenyl- 
hydrazine.  Lob  has  also  found  that  moist  carbon  dioxide 
yields  formaldehyde  under  the  influence  of  the  silent  electric 
discharge  (Zeit.  Electrochemie,'1905,  11,  745;  1906,  12,  282). 


CLASS  II— CHEM18TE.Y  OF  THE  CYCLIC 
COMPOUNDS 


XV.  INTRODUCTION 

The  compounds  which  have  been  treated  of  in  Sections  I  to 
XIV  are  derivable  from  the  homologous  hydrocarbons  CnH2n+2, 
CnH2n,  CnH2n_2,  &c.,  by  the  exchange  of  hydrogen  for  halogen, 
hydroxyl  or  oxygen,  amidogen,  carboxyl,  &c.  ;  and  since  all  the 
hydrocarbons  already  mentioned  may  also  be  regarded  as  deri- 
vatives of  methane  (e.g.  C2H6  =  CH3(CH3)  =  methyl-methane, 
C3H8  =  CH2(CH3)2  =  dimethyl-methane,  C2H4  =  CH2:CH2 
=  methylene-methane,  C2H2  =  CHjCH  =  methine-methane, 
&c.),  we  may  term  the  compounds  which  have  been  described 
in  the  foregoing  portion  of  this  book  methane  derivatives. 

As  nearly  all  these  compounds  have  open-chain  formulae, 
they  are  spoken  of  as  open-  chain  compounds,  or  often  ali- 
phatic compounds. 

But  in  addition  to  this  first  class  of  organic  compounds 
there  is  a  second  great  class,  viz.  that  of  the  closed-chain  com- 
pounds. The  old  classification  was  into  aliphatic  or  methane  de- 
rivatives and  aromatic  or  benzene  derivatives.  The  expression 
"aromatic"  is  historical,  but  no  longer  justified  by  facts,  since 
compounds  of  agreeable  as  well  as  unpleasant  odour  are  to  be 
found  in  both  classes.  The  members  of  this  second  class  which 
are  derivable  from  the  hydrocarbon  benzene,  C6H6  (and  also 
from  more  complicated  hydrocarbons  such  as  anthracene,  naph- 
thalene, &c.,  which  are  themselves  derivatives  of  benzene),  just 
as  the  methane  derivatives  are  from  methane,  are  designated 
benzene  derivatives. 

Eecent  investigations  have  led  to  the  discovery  of  numerous 
other  cyclic  compounds  which  cannot  be  regarded  as  simple 
derivatives  of  benzene,  e.g.  : 

CH  CH:CH\ 

7 


(B480)  321 


322  XVI.   POLYMETHYLENE  DERIVATIVES 

and  hence  the  modern  classification  of  the  cyclic  compounds  is 
into: — 

A.  Carbocyclic  or  Isocyclic. — In  all  these  compounds  the 
ring  or  closed  chain  is  composed  entirely  of  carbon  atoms. 
The  carbocyclic  compounds  are  usually  divided  into — 

(i)  Polymethylene  derivatives  or  naphthenes. 
(ii)  Benzene  derivatives  or  aromatic  compounds,  including 
the  allied  compounds  naphthalene,  anthracene,  &c. 

B.  Heterocyclic  Compounds. — In  these  compounds  the  closed 
ring  is  formed  partly  of  carbon  atoms  and  partly  of  atoms  of 
other  elements.     Well-known  examples  are: 

CH:CH\  CH:CH\ 

>O  (furane),  •  >S  (thiophene), 

mr.r<TT/  mr-mr/ 

V/JCL  •  yy  Ji-  t^Ji  .  VyJd' 

\NH  (pyrrole),      CH<^SS;S5^N  (pyridine),    &c. 
vv-tL  1  Oxi.' 


CAKBOCYCLIC   COMPOUNDS 

XVI.  POLYMETHYLENE  DERIVATIVES 

The  hydrocarbons  from  which  all  these  compounds  are 
derived  consist  of  three  or  more  methylene  groups  united 
together  to  form  a  closed  ring.  The  names  for  the  specific 
hydrocarbons  indicate  the  number  of  such  groups,  e.g. : 

2  ^-tl-2  *  ^-^-2 

(trimethylene),  |  J_    (tetramethylene), 


/CH2«2  ^nr  PTT  v. 

CH2<  |         (pentamethylene),   CH2<X^2  '  ™2NCH2  (hexamethylene). 

x!H.CH  ^£L2'V,n2 


The  systematic  names  for  these  compounds  are  cyclo-pro- 
pane,  cyclo-butane,  &c.,  although  the  compounds  are  isomeric 
with  the  defines,  and  have  the  same  general  formula,  CnH2n. 
The  above  names  indicate  the  fact  that  the  compounds  are  in 
a  sense  saturated. 

Eelative  Stability  of  Polymethylene  Compounds.—  It  has 
been  found  that  the  majority  of  trimethylene  derivatives  are 
relatively  unstable;  to  a  certain  extent  they  resemble  ethylene. 


FORMATION   OF  POLYMETHYLENE  COMPOUNDS  323 

oxide,  and  are  capable  of  forming  additive  products  by  the 
rupture  of  the  ring.  Thus  bromine  slowly  transforms  tri- 
methylene  under  the  influence  of  sunlight  into  trimethylene 
dibromide : 


CK/  I        —  .  CH2Br.CH2.CH2Br. 


Tetramethylene  derivatives  are  somewhat  more  stable,  and 
penta-  and  hexa-methylene  derivatives  are  remarkably  stable 
and  show  little  or  no  tendency  towards  the  rupture  of  the 
molecule. 

These  facts  are  in  harmony  with  Ba&yer's  tension  theory. 
If  the  four  valencies  of  the  tetravalent  carbon  atom  are 
assumed  to  be  symmetrically  distributed  in  space  around  the 
carbon  atom,  it  is  found  that  ring  formation  in  the  case  of  a 


/2 
compound  CH2<\  |       can  only  take  place  by  the  exercise  of 

CH2 

a  considerable  strain  in  the  molecule;  hence  when  the  ring 
formation  is  completed  there  is  considerable  tendency  for  it  to 
spring  apart  or  rupture  at  some  point.  With  penta-  and  hexa- 
methylene  compounds,  on  the  other  hand,  it  can  be  seen  by 
the  aid  of  models  that  practically  no  strain  is  required  to  com- 
plete the  ring  formation,  and  thus  the  rings  when  once  formed 
are  relatively  stable. 

GENERAL  METHODS  OF  FORMATION 

1.  By  the  action  of  sodium  on  dihalogen  derivatives  of  the 
paraffins  (Freund).  The  two  halogen  atoms  must  not  be 
attached  to  the  same  or  to  adjacent  carbon  atoms. 


CH2.CH2Br  CH2.CH2 

+  2Na  =  2NaBr  +  I 
CH2-CH2Br 


2.  Acids  and  their  esters  can  be  obtained  by  the  conden- 
sation of  ethyl  sodio-malonate  with  ethylene  dibromide  and 
other  dihalogen  derivatives  (W.  H.  Perkin,  Jun.): 

fNa2C(C02Et)2  = 


324  XVI.   POLYMETHYLENE  DERIVATIVES 

and  the  ester  on  hydrolysis  yields  trimethylene-dicarboxylic 
acid. 

Ethyl  acetoacetate  may  be  substituted  for  ethyl  malonate. 

3.  By  the  action  of  halogens  (bromine,  or  preferably  iodine) 
on  the  sodio-derivatives  of  certain  esters,  e.g.  sodio-derivative 
of  ethyl  butane-tetracarboxylate  (W.  H.  Perkin,  Jun.): 

CH2.CNa<C02Et)2  CH2-C(CO2Et)2 

CH2.CNa(C02Et)2        2  *  CH2.C(CO2Et)2. 

4.  By  intramolecular  pinacone  formation.     Just  as  ketones 
on  reduction  yield  pinacones  : 

(CH3)2.C:0  , 
(CH3)2.C:0  +  - 

(cf.  p.  191),  so  certain  diketones  on  reduction  yield  cyclic 
pinacones,  i.e.  dihydric  alcohols  derived  from  the  polymethy- 
lene  hydrocarbons: 

H.CO.CH3        H  xCH2.C(OH).CH3 

O.CH3  +  'H2\CH2.C(OH).CH3 

1  :  2-Dimethyl-l  :  2-dihydroxy 
cyclo-pentane. 

5.  A  number  of  ketones  derived  from  the  polymethylenes 
have  been  obtained  by  the  dry  distillation  of  the  calcium  salts 
of  the  higher  dibasic  acids  of  the  oxalic  series  (/.  Wislicenus\ 
e.g.  calcium  adipate  yields  keto-pentamethylene  : 

CH2  •  CH2  •  CO  •  O\  CH2  •  CH 

;   .       CH2.CH2.CO.O>  =  Ca 

and  this  can  be  reduced  to  pentamethylene.  The  constitution 
of  the  keto-derivative  follows  from  the  fact  that  on  oxidation 
the  ring  is  ruptured  and  glutaric  acid  is  formed. 

Keto-hexamethylene  and  keto-heptamethylene  or  suberone 
have  been  obtained  by  similar  methods,  but  the  yield  is  not  so 
good  in  these  two  cases. 

6.  Hexamethylene  compounds  are  often  obtained  by  the 
reduction  of  benzene  derivatives  with  sodium  and  alcohol: 


General  Properties.  —  On  the  whole  these  compounds  some- 
what closely  resemble  the  paraffins  as  regards  their  chemical 


ISOMERISM   OF  POLYMETHYLENE  COMPOUNDS  325 

properties,  hence  the  names  cyclo-pentane  for  pentamethylene, 
cyclo-hexane,  &c. 

The  trimethylene  compounds,  however,  resemble  the  de- 
fines, e.g.  (a)  they  can  combine  with  bromine  to  form  additive 
compounds;  (b)  they  are  slowly  oxidized  by  permanganate. 
In  neither  of  these  reactions  do  they  take  part  so  readily  as 
;iae  simpler  olefines,  and  in  all  cases  the  products  obtained  are 
formed  at  the  expense  of  the  rupture  of  the  ring. 

The  fact  that  the  majority  of  the  hydrocarbons  of  this  series 
resemble  paraffins  indicates  that  the  formation  of  a  closed  chain 
does  not  affect  to  any  considerable  extent  the  properties  of 
a  compound  (cf.  Benzene). 

In  their  chemical  properties  the  compounds  closely  resemble 
the  corresponding  derivatives  of  the  paraffins,  e.g.  the  acids 
resemble  to  a  large  extent  the  fatty  acids,  yielding  salts,  esters, 
acid  chlorides,  amides,  &c. 

Isomerism. — (a)  Position  Isomerism. — No  examples  of  iso- 
merism  have  been  met  with  in  the  case  of  mono-substituted  de- 
rivatives, e.g.  only  one  tetramethylenecarboxylic  acid  is  known. 
Position  isomerism  can  occur  in  the  case  of  di-  and  poly-sub- 
stituted derivatives,  e.g.  tetramethylene-1  :l-dicarboxylic  acid 
and  isomeric  1 : 2  and  1 : 3  acids. 


4     '  l:2-Dicarboxylic  acid 

l:l-Dicarboxylic  acid 


COoH-C 

^V^-LJ-2' 

l:3-Dicarboxylic  acid. 

The  number  of  isomerides  possible  in  each  case  can  be  worked 
out  by  the  student  (cf.  Benzene  Derivatives). 

(b)  Stereo -isomerism.  —  Certain  di- substituted  derivatives 
have  been  found  to  exist  in  isomeric  forms  which  are  struc- 
turally identical.  These  must  therefore  be  stereo-isomeric. 
Some  of  the  simplest  examples  of  this  stereo-isomerism  are 
met  with  in  the  dibasic  acids.  For  example: 

Tetramethylene-l:2-dicarboxylic  acid  exists  in  two  isomeric 
forms.  In  both  acids  the  2C02H  groups  are  Attached  to  the 
carbon  atoms  1  and  2,  and  the  only  difference  is  in  the  relative 
spatial  relationships  of  the  groups.  If  the  plane  of  the  paper 
represents  the  plane  in  which  the  centres  of  gravity  of 


326  XVI.    POLYMETHYLKNE  DERIVATIVES 

the  four  carbon  atoms  of  the  ring  lie,  then  the  possibilities 
are — 

H  C02H 


(I)  cis. 

(I)  That  the  two  C02H  groups  lie  in  the  same  plane  either 
above  or  below  the  plane  of  the  paper  (this  is  known  as  the  tis 
acid) ;  and  (II)  that  the  two  C02H  groups  lie  in  different  planes, 
one  above  and  one  below  the  plane  of  the  paper  (this  is 
known  as  the  trans  acid).  As  a  rule,  the  cis  acids  yield  inner 

f^O 
anhydrides,  e.g.  C4H6<^QQ^>0,  more  readily  than  the  stereo- 

isomeric  trans  acids,  and  the  cis  acids  are  generally  transformed 
into  the  corresponding  trans  acids  when  heated  with  hydro- 
chloric acid  at  190°.  (Cf.  Perkin,  Jun.,  J.  C.  S.  1894,  572.) 

A  simple  method  of  depicting  these  isomerides  is  due  to 
Aschan  (B.  1902,  35,  3389). 

The  plane  of  the  carbon  atoms  of  the  ring  is  represented 
by  a  straight  line.  The  unsubstituted  hydrogen  atoms  are 
not  denoted,  only  those  which  have  been  replaced  by  sub- 
stituents.  It  has  been  found  that  the  symmetry  of  such  pro- 
jections corresponds  with  the  symmetry  of  the  molecules 
projected.  For  the  cis  dicarboxylic  acids,  for  example,  if 
C02H  =  X,  we  have: 

X_*          and          ^_  _^ 

(I)  cis.  (H)  trans.  (III). 

The  cis  compound  (I)  is  not  perfectly  asymmetric,  whereas 
the  trans  compound  (II)  is.  Corresponding  with  (II)  is  a  third 
isomeride,  which  stands  in  the  same  relationship  to  (II)  as  an 
object  to  its  mirror  image,  or  as  d-  to  Z-lactic  acids.  Both 
should  therefore  be  optically  active  (one  d  and  the  other  I  to 
the  same  extent),  and  should  be  capable  of  combining  to  yield 
a  racemic  compound.  All  the  trans  compounds  prepared  arti- 
ficially are  optically  inactive,  and  are  presumably  therefore 
racemic  compounds  of  (II)  and  (III),  although  so  far  very  few 
have  been  resolved  into  optically  active  components. 


fcENZENE  DERIVATIVES  32^ 

Intermediate  between  the  polymethylene  compounds  and 
benzene  derivatives  are  the  reduction  products  of  benzene 
and  its  derivatives,  e.g.  di-  and  tetra-hydrobenzene,  tetrahydro- 
phthalic  acid,  &c.,  C6H8,  C6H10,  C6H8(C02H)2.  These  will  be 
discussed  along  with  the  benzene  compounds,"  from  which  they 
are  derived. 


XVII.  BENZENE  DERIVATIVES.    INTRODUCTION 

Benzene  is,  as  its  formula  C6H6  shows,  a  compound  much 
poorer  in  hydrogen  than  the  paraffins,  containing  8  hydrogen 
atoms  less  than  hexane,  C6HJ4;  in  the  same  way  all  benzene 
derivatives  are  much  poorer  in  hydrogen,  i.e.  richer  in  carbon 
than  the  analogous  methane  derivatives,  as  is  seen  by  com- 
paring e.g.  benzoic  acid,  CrH602,  with  heptoic  acid,  C7H1402, 
or  aniline,  C6H7N,  with  ethylamine,  G2H7N,  &c. 

The  hydrogen  atoms  of  benzene  are,  like  those  of  methane, 
replaceable  by  numerous  types  of  radicals.  By  the  entrance 
of  halogens,  halide  substitution  products  are  formed,  by  the 
entrance  of  NH2,  aromatic  bases,  of  OH,  phenols,  of  N02, 
nitro-compounds,  and  of  CH3,  &c.,  the  homologues  of  benzene; 
there  are,  in  addition  to  these,  aromatic  alcohols,  aldehydes, 
acids,  &c. 

These  benzene  derivatives  are  partly  analogous  in  their 
properties  to  the  methane  derivatives  of  corresponding  com- 
position; in  part,  however,  they  show  new  and  peculiar  pro- 
perties of  their  own  (see  pp.  328  et  seq.).  One  distinguishes 
between  mono-,  di-,  tri-,  &c.,  substituted  benzene  derivatives 
according  as  1,  2,  or  more  hydrogen  atoms  are  replaced  by 
the  various  radicals;  thus,  for  instance,  toluene,  C6H5»CH3, 
and  chloro-benzene,  C6H5-C1,  are  mono-derivatives,  dimethyl- 
benzene,  C,H4(CH3)2,  and  dichloro-benzene,  C6H4C12,  di-deri- 
vatives,  and  so  on.  It  is  not  necessary  that  the  substituents 
should  be  identical,  so  that  innumerable  compounds  are  known 
containing  various  substituents,  e.g.  OH»C6H4-N02,  nitro- 

Shenol;   C6H4Br«S03H,  bromobenzene-sulphonic  acid;   CH3« 
6H3(NO2)2,  dinitro-toluene.     Such  compounds  have  usually 
some  of  the  characteristics  of  all  those  mono-derivatives  which 
result  from  benzene  by  the  exchange  of  one  hydrogen  atom 
for  one  of  these  substituents. 

All  the  derivatives  of  benzene  can  be  converted  either  into 
benzene  itself  or  into  very  closely  allied  compounds  by  rcla- 


326  XVI.   POLYMETHYLENE  DERIVATIVES 

the  four  carbon  atoms  of  the  ring  lie,  then  the  possibilities 
are — 

H 


(I)  cis. 

(I)  That  the  two  C02H  groups  lie  in  the  same  plane  either 
above  or  below  the  plane  of  the  paper  (this  is  known  as  the  cis 
acid);  and  (II)  that  the  two  C02H  groups  lie  in  different  planes, 
one  above  and  one  below  the  plane  of  the  paper  (this  is 
known  as  the  trans  acid).  As  a  rule,  the  cis  acids  yield  inner 

anhydrides,  e.g.  C4H6<^pQ^>0,  more  readily  than  the  stereo- 

isomeric  trans  acids,  and  the  cis  acids  are  generally  transformed 
into  the  corresponding  trans  acids  when  heated  writh  hydro- 
chloric acid  at  190°.  (Cf.  Perkin,  Jun.,  J.  C.  S.  1894,  572.) 

A  simple  method  of  depicting  these  isomerides  is  due  to 
Aschan  (B.  1902,  35,  3389). 

The  plane  of  the  carbon  atoms  of  the  ring  is  represented 
by  a  straight  line.  The  unsubstituted  hydrogen  atoms  are 
not  denoted,  only  those  which  have  been  replaced  by  sub- 
stituents.  It  has  been  found  that  the  symmetry  of  such  pro- 
jections corresponds  with  the  symmetry  of  the  molecules 
projected.  For  the  cis  dicarboxylic  acids,  for  example,  if 
C02H  =  X,  we  have: 

^^  and  ^_  __* 


(I)  cis.  (II)  trans.  (III). 

The  cis  compound  (I)  is  not  perfectly  asymmetric,  whereas 
the  trans  compound  (II)  is.  Corresponding  with  (II)  is  a  third 
isomeride,  which  stands  in  the  same  relationship  to  (II)  as  an 
object  to  its  mirror  image,  or  as  d-  to  /-lactic  acids.  Both 
should  therefore  be  optically  active  (one  d  and  the  other  /  to 
the  same  extent),  and  should  be  capable  of  combining  to  yield 
a  racemic  compound.  All  the  trans  compounds  prepared  arti- 
ficially are  optically  inactive,  and  are  presumably  therefore 
racemic  compounds  of  (II)  and  (III),  although  so  far  very  few 
have  been  resolved  into  optically  active  components. 


6ENZENE  DERIVATIVES  32 1 

Intermediate  between  the  polymethylene  compounds  and 
benzene  derivatives  are  the  reduction  products  of  benzene 
and  its  derivatives,  e.g.  di-  and  tetra-hydrobenzene,  tetrahydro- 
phthalic  acid,  &c,  C6H8,  C6H10,  C6H8(C02H)2.  These  will  be 
discussed  along  with  the  benzene  compounds,  from  which  they 
are  derived. 


XVII.  BENZENE  DERIVATIVES.    INTRODUCTION 

Benzene  is,  as  its  formula  C6H6  shows,  a  compound  much 
poorer  in  hydrogen  than  the  paraffins,  containing  8  hydrogen 
atoms  less  than  hexane,  C6HJ4;  in  the  same  way  all  benzene 
derivatives  are  much  poorer  in  hydrogen,  i.e.  richer  in  carbon 
than  the  analogous  methane  derivatives,  as  is  seen  by  com- 
paring e.g.  benzoic  acid,  CrH602,  with  heptoic  acid,  C7H1402, 
or  aniline,  C6H7N,  with  ethylamine,  C2HrN,  &c. 

The  hydrogen  atoms  of  benzene  are,  like  those  of  methane, 
replaceable  by  numerous  types  of  radicals.  By  the  entrance 
of  halogens,  halide  substitution  products  are  formed,  by  the 
entrance  of  NH2,  aromatic  bases,  of  OH,  phenols,  of  N02, 
nitro-compounds,  and  of  CH3,  &c.,  the  homologues  of  benzene; 
there  are,  in  addition  to  these,  aromatic  alcohols,  aldehydes, 
acids,  &c. 

These  benzene  derivatives  are  partly  analogous  in  their 
properties  to  the  methane  derivatives  of  corresponding  com- 
position; in  part,  however,  they  show  new  and  peculiar  pro- 
perties of  their  own  (see  pp.  328  et  seq.).  One  distinguishes 
between  mono-,  di-,  tri-,  &c.,  substituted  benzene  derivatives 
according  as  1,  2,  or  more  hydrogen  atoms  are  replaced  by 
the  various  radicals;  thus,  for  instance,  toluene,  C6H5'CH3, 
and  chloro-benzene,  C6H5-C1,  are  mono-derivatives,  dimethyl- 
benzene,  C,H4(CH3)2,  and  dichloro-benzene,  C6H4C12,  di-deri- 
vatives,  and  so  on.  It  is  not  necessary  that  the  substituents 
should  be  identical,  so  that  innumerable  compounds  are  known 
containing  various  substituents,  e.g.  OH  .C6H4-NO2,  nitro- 
phenol;  C6H4Br«S03H,  bromobenzene-sulphonic  acid;  CH3. 
C6H3(N02)2,  dinitro-toluene.  Such  compounds  have  usually 
some  of  the  characteristics  of  all  those  mono-derivatives  which 
result  from  benzene  by  the  exchange  of  one  hydrogen  atom 
for  one  of  these  substituents. 

All  the  derivatives  of  benzene  can  be  converted  either  into 
benzene  itself  or  into  very  closely  allied  compounds  by  rela- 


328          XVII.   BENZENE  DERIVATIVES.      INTRODUCTION 

lively  simple  reactions.  Thus  all  the  carboxylic  acids  of  ben- 
zene (benzoic,  phthalic,  mellitic,  &c.)  yield  benzene  on  dis- 
tillation with  lime,  while  other  acids,  such  as  salicylic,  evolve 
C02  and  yield  phenol;  the  last-named  compound  is  converted 
into  benzene  when  distilled  with  zinc  dust.  The  homologues 
of  benzene  are  converted  by  oxidation  into  benzene-carboxylic 
acids,  which  yield  benzene  when  heated  with  lime. 

The  relationship  of  a  benzene  derivative  to  its  mother  substance  is 
therefore  a  very  simple  one. 

This  circumstance  is  one  particularly  worthy  of  note,  since 
the  atomic  group  C6H6  is  already  a  tolerably  complicated 
molecule  in  itself,  and  also  because  benzene  cannot  by  any 
means  be  transformed  into  a  simpler  hydrocarbon  containing 
5,  4,  or  3  carbon  atoms;  when  oxidized,  which  is  a  matter  of 
difficulty,  it  yields  carbonic  or  similar  simple  organic  acids. 

The  benzene  derivatives  are  connected  with  one  another  by 
the  most  varied  reactions.  The  N02  group  is  readily  con- 
vertible into  NH2,  and  the  latter  is  replaceable  by  halogen, 
hydrogen,  and  hydroxyl;  the  halogen  is  also  replaceable  by 
methyl,  carboxyl,  &c. 

As  a  rule,  the  group  of  6  carbons  with  the  hydrogens  is 
spoken  of  as  the  benzene  nucleus,  and  all  substituents  are 
spoken  of  as  side  chains.  Thus  in  C6H5-CHO,  C6H4*(CH3)2, 

C6H5»NH2  the  radicals  underlined  are  the  side  chains. 

o 

CHARACTERISTIC  PROPERTIES  OF  BENZENE  DERIVATIVES 

In  many  chemical  properties  benzene  and  its  derivatives 
differ  markedly  from  the  paraffins  or  unsaturated  open-chain 
hydrocarbons. 

1.  The  aromatic  hydrocarbons  and  their  derivatives  are 
readily  attacked  by  concentrated  nitric  acid,  yielding  nitro- 
derivatives : 


Certain  of  the  higher  paraffins  also  yield  nitro-derivatives 
when  heated  with  nitric  acid  (p.  95). 

2.  Sulphonic  acids  are  readily  formed  by  the  action  of  con- 
centrated or  fuming  sulphuric  acid  : 


02.OH  =  H20  +  CCH5.S02.OH. 
This  type  of  reaction  is  never  met  with  in  the  aliphatic  series. 


tSOMERISM  OF  BENZEKE  DERIVATIVES  329 

3.  The   homologues   of  benzene  differ  from   the  paraffins 
especially  as   regards   oxidation;  while  the  latter  are   only 
attacked  with  difficulty  by  oxidizing  agents,  the  former  are 
readily  converted  into  benzene-carboxylic  acids: 

C6H5.CH3  —  C6H6.C02H. 

4.  The  halogens  chlorine  and  bromine  can  react  with  ben- 
zene in  two  distinct  ways :  (a)  yielding  substituted  derivatives, 
e.g.  C^Hg  +  Br2  =  C6H5Br  +  HBr,  or  (b)  yielding  additive 
products,  e.g.  C6H6Br6. 

The  process  of  substitution  is  the  more  important  and  the 
commoner  of  the  two  reactions. 

5.  There  are  not  wanting  other  distinguishing  characteristics 
between  the  aromatic  hydrocarbons  and  the  paraffins.     Thus 
the  halogen  compounds  C6H5X  are  chemically  less  active,  and 
the  hydroxyl  compounds,  e.g.  C6H5(OH),  are  of  a  more  acidic 
nature  than  the  corresponding  fatty  bodies.   The  phenyl  radical, 
C6H5,  is  therefore  more  acid  or  "  negative  "  in  character  than 
the  ethyl,  C2H5  (cf.  V.  Meyer,  B.  20,  534,  2944;  A.  250,  118). 

6.  Diazo-compounds  are  far  more  common  in  the  aromatic 
series  than  in  the  aliphatic. 

ISOMERIC  RELATIONS 

1.  While  several  isomeric  mono-derivatives  are  both  theo- 
retically possible  and  have  been  actually  obtained  from  each 
hexane,  CgH^,  benzene  is  only  capable  of  forming  a  single 
mono -derivative  in  each  case;  isomeric  mono -derivatives  of 
benzene  are  unknown.  The  six  hydrogen  atoms  of  benzene  thus 
possess  an  equal  value,  or  are  similarly  situated  within  the  molecule. 
This  is  not  merely  an  empirical  law,  but  one  which  has  been 
proved  experimentally. 

PROOF  OF  THE  EQUAL  VALUE  OF  THE  SIX  HYDROGEN 

ATOMS 

Let  the  6  H  atoms  be  designated  as  a,  b,  c,  d,  e,  and  / 
respectively. 

(1)  Phenol,  C6H5(OH),  whose  hydroxyl  may  have  replaced 
the  H  atom  a,  may  be  converted  into  bromo-benzene,  C6H5Br, 
and  this  latter  into  benzoic  acid,  C6H5(C02H).  The  carboxyl 
in  the  latter  has  therefore  also  the  position  a,  i.e.  it  has  re- 
placed the  H  atom  a. 


330         XVII.   BENZENE  DERIVATIVES.      INTRODUCTION 

(2)  Three  hydroxy-benzoic  acids,   C6H4(OH)(C02H),    can 
either  be  prepared  from  benzoic  acid  or  converted  into  it; 
their  carboxyl  therefore  has  the  position  a,  and  consequently 
their  hydroxyl  must  replace  some  one  of  the  other  H  atoms, 
be  it  5,  c,  or  d. 

(3)  Each  hydroxy-benzoic  acid  can  be  decomposed,  yielding 
carbon  dioxide  and  ordinary  phenol,  C6H6OH: 

C6H4(OH)(C02H)  =  C6H5(OH)  +  C02. 

And  since  the  latter  compound  contains  the  hydroxyl  in 
position  a,  according  to  (1),  while  the  hydroxyl  in  the  hy- 
droxy-benzoic acids  replaces  the  H  atoms  b,  c,  and  d,  it  follows 
that  the  hydrogen  atoms  a,  b,  c,  and  d  are  of  equal  value. 

(4)  Now,  as  will  be  explained  on  p.  331,  for  each  H  atom 
there  are  present  two  other  pairs  of  symmetrical  hydrogen 
atoms,  i.e.  pairs  of  which  either  the  one  or  the  other  atom 
may  be  replaced  by  any  given  radical  without  different  sub- 
stances resulting.     But  the  atoms  of  such  a  pair  cannot  both 
be  present  in  the  positions  a,  b,  c,  and  d,  as  in  this  case  three 
hydroxy-benzoic  acids  could  not  exist.     It  must  therefore  be 
the  remaining  H  atoms  e  and  /  which  are  respectively  in  posi- 
tions symmetrically  situated  to  two  of  the  former,  and  which 
are  therefore  of  equal  value  with  them,  i.e.  e  =  c,  f  =  b.    Since, 
however,  a  =  b  =  c  =  d,  it  follows  that  all  the  6  hydrogen 
atoms  are  of  equal  value  (Ladenburg,  B.  7,  1684). 

2.  With  di-substituted  derivatives  of  benzene  it  has  been 
found  that  in  each  case  three  distinct  isomeric  forms  exist. 
The  two  substituents  may  be  alike,  or  they  may  be  dis- 
similar, e.g.  three  dichloro-benzenes,  C6H4C12,  three  diamino- 
benzenes,  C6H4(NH2)2,  three  dimethyl-benzenes,  C6H4(CH3)2, 
three  hydroxy-benzoic  acids,  C6H4(OH)(C02H),  are  known. 
In  no  case  have  more  than  three  such  isomerides  been  found. 

It  can  be  shown  that  with  respect  to  each  H  atom  of  ben- 
zene, e.g.  for  a,  two  pairs  of  other  H  atoms,  e.g.  b  and  /,  c  and  e, 
are  symmetrically  situated,  so  that  it  makes  no  difference 
whether,  after  a  is  replaced,  the  second  substituent  replaces 
the  one  or  the  other  of  the  symmetrically  placed  hydrogen 
atoms,  say  b  or  /.  According  to  the  above  notation,  there- 
fore, ab  =  aft  and  ac  =  ae.  On  the  other  hand,  the  com- 
binations ab  and  ac  are  not  equivalent,  but  represent  isomers; 
the  combination  ad,  the  only  remaining  case,  represents  the 
third  isomer. 


CONSTITUTION  OF  BENZENE  331 


PROOFS  THAT  FOR  EVERY  H  ATOM  (a)  TWO  OTHER  PAIRS 
OF  SYMMETRICALLY  LINKED  H  ATOMS  EXIST 

1.  According  to  Hubner  and  Petermann  (A.  149,  129;  cf. 
also  Hubner,  A.  222,  67,  166),  the  (so-called  meta-)  bromo- 
benzoic  acid,  which  is  obtained  by  brominating  benzoic  acid, 
and  whose  Br  atom  may  be  in  position  c  and  C02H  in  posi- 
tion a,  yields  with  nitric  acid  two  nitrobromo-benzoic  acids, 
C6H3Br(N02)(C02H),  the  N02  being,  say,  in  positions  b  and/. 
These  are  both  reduced  by  nascent  hydrogen  to  the  same  (so- 
called  ortho-)  amino-benzoic  acid,  C6H4(NH2)(C02H),  the  N02 
being  here  changed  to  NH2  and  the  Br  replaced  by  H.     Since 
the  same  amino-benzoic  acid  is  formed  in  both  cases,  notwith- 
standing that  the  nitro-groups  must  be  in  the  place  of  different 
H  atoms,  say  b  and  /,  from  the  fact  of  the  two  nitro-acids 
being  dissimilar,  it  follows  that  b  and  /  must  be  arranged  sym- 
metrically as  regards  the  H  atom  a,  i.e.  ab  —  af. 

2.  In  an  analogous  manner  salicylic  acid,  C6H4(OH)(C02H), 
which  can  be  prepared  from  the  above-mentioned  amino-ben- 
zoic acid,  yields  two  nitro-derivatives,  C6H3(OH)(N02)(C02H). 
If,  however,  the  hydroxyl  in  these  is  replaced  by  hydrogen  (a 
reaction  which  can  be  effected  by  indirect  methods),  the  nitro- 
benzoic  acids  thus  obtained,  C6H4(N02)(G02H),  are  identical, 
and  therefore   the  H   atoms  which  have  been  replaced  by 
N02  are  in  position^  symmetrical  to  a.      When  this  nitro- 
benzoic  acid  is   in  its   turn  reduced  to  amino-benzoic  acid, 
C6H4(NH2)(C02H),  it  is  not   the  above  (ortho-)  amino-acid 
(where  ab  =  af)  which  is  obtained,  but  an  isomer.     The  N02 
groups  cannot  therefore  here  be  in  the  positions  b  and  /,  but 
must  replace  two  other  H  atoms  which  are  likewise  symmetric 
towards  a,  say  c  and  e,  i.e.  ac  —  ae  (Hubner,  A.  195,  4). 

Thus  two  pairs  of  H  atoms  are  symmetrically  situated  as 
regards  the  H  atom  a:  ab  =  afj  ac  =  ae.  There  remains 
only  the  third  possible  combination  ad]  the  sixth  H  atom  d 
is  situated  towards  the  first  a  in  a  position  of  its  own,  i.e.  in 
one  to  which  there  is  no  corresponding  position. 

For  further  particulars,  cf.  Ladenburg,  "Theorie  der  aromat. 
Verbindungen ",  Braunschweig,  1876;  WroUewsky,  A.  168, 
153;  192,  196;  B.  8,  573;  9,  1055;  18,  Ref.  148.  Noelling, 
B.  1904,  37,  1015,  gives  a  very  simple  proof. 

It  has  been  assumed  in  the  considerations  just  detailed 
that  when  one  compound  is  converted  into  another  by  tho 


332          XVII.   BENZENE  DERIVATIVES.      INTRODUCTION 

exchange  of  atoms  or  radicals  (NH2  for  N02,  H  for  OH),  this 
exchange  is  effected  without  a  so-called  "  molecular  rearrange- 
ment" taking  place  at  the  same  time  (see  p.  132).  Experience 
has  proved  that  this  may  be  taken  for  granted  in  a  large 
number  of  reactions  which  proceed  with  relative  smoothness 
and  at  comparatively  low  temperatures.  Those  instances  in 
which  a  molecular  rearrangement  ensues  are  now  well  known ; 
especially  is  this  the  case  in  the  fusion  of  sulphonic  acids 
with  potash  (exchange  of  S03H  for  OH),  a  reaction  which 
takes  place  at  relatively  high  temperatures  only,  and  which 
frequently  leads  to  isomers  of  the  compounds  expected.  In 
other  reactions  which  occur  at  high  temperatures  a  rearrange- 
ment of  the  atoms  in  the  molecule  can  also  take  place.  Thus, 
when  potassium  ortho-hydroxy-benzoate  is  heated  to  220°,  the 
potassium  salt  of  the  para-acid  is  formed;  the  three  isomeric 
bromo-benzene-sulphonic  acids,  C6H4Br(S03H),  and  the  three 
bromo-phenols,  C6H4Br(OH),  yield  only  meta-dihydroxy -benzene 
(resorcinol),  C6H4(OH)2,  when  fused  with  potash,  and  not  the 
three  isomeric  dihydroxy -benzenes;  ortho- phenol -sulphonic 
acid,  C6H4(OH)S03H,  yields  the  para-acid  when  heated.  Re- 
actions of  this  nature  probably  arise  from  the  successive  taking 
up  and  splitting  off  of  atoms  or  atomic  groups. 

CONSTITUTION   OF   BENZENE 

The  formula  C6H6  at  once  indicates  that  benzene  cannot  be 
a  saturated  open-chain  compound.  The  possibility  that  it  is 
an  open-chain  unsaturated  compound  containing  several  double 
or  triple  bonds  has  been  shown  to  be  untenable,  e.g.  dipro- 
pargyl  (p.  53),  CH:C.CH2.CH2.CiCH,  although  resembling 
benzene  in  physical  properties,  is  quite  different  as  regards 
most  of  its  chemical  properties;  it  combines  readily  with  bro- 
mine, yielding  additive  compounds  with  2,  4,  6,  or  8  atoms  of 
bromine,  and  it  is  also  oxidized  with  the  greatest  readiness. 
Benzene  combines  with  bromine  only  slowly  and  under  specific 
conditions,  and  then  yields  C6H6Br6;  it  is,  further,  extremely 
stable  towards  oxidizing  agents.  The  equivalency  of  the 
6  hydrogen  atoms  in  the  benzene  molecule  is  a  further  strong 
argument  against  such  open-chain  formulae.  KehiU  was  the 
first  to  suggest  a  closed -chain,  cyclic,  or  ring  formula  for 
benzene. 

In  order  to  account  for  the  existence  of  only  one  mono- 
substituted  derivative,  C6H6X,  but  of  three  isomeric  di-sub 


ISOMERISM   OF   BENZENE  DERIVATIVES  333 

stituted  derivatives,  C^H^Xg,  it  is  necessary  to  assume  that 
a  single  hydrogen  atom  is  attached  to  each  carbon  atom. 


CH 


This  formula  is  usually  known  as  the  benzene  ring. 

In  the  above  formula  the  six  hydrogen  atoms  are  symmetri- 
cally placed  with  respect  to  one  another,  and  thus  in  the  for- 
mation of  a  mono-substituted  derivative  it  is  immaterial  which 
one  of  the  six  hydrogens  is  replaced;  only  one  compound, 
C6H5X,  can  be  formed. 

With  di-substituted  derivatives  three  isomerides  are  theo- 
retically possible,  viz.: 


the  1:2  or  ortho-compound,  1:3  or  meta-compound,  and  the 
1:4  or  para-compound. 

The  compound  1:5  is  identical  with  1:3,  and  1:6  is  identical 
with  1:2.  Cf.  JPohl,  B.  1910,  43,  3474. 

The  hydrogen  atoms  in  positions  2 : 6  form  one  pair  of  sym- 
metrical hydrogen  atoms  mentioned  on  p.  329,  and  those  in 
positions  3:5  form  the  second  pair,  whereas  the  hydrogen  in 
position  4  has  no  other  hydrogen  atom  corresponding  with  it. 

Similarly,  three  tri-substituted  derivatives,  C6H3X3,  are 
known,  and  only  three  are  possible  with  such  a  ring  formula, 
viz. : 

XXX 

(III) 


(I)  1:2:3  or  adjacent  tri-derivative. 

(II)  1 : 3 : 5  or  sym.  tri-derivative. 

(III)  1:2:4  or  unsym.  tri-derivative. 

Any  other  combination  is  identical  with  one  of  these,  2:4:6 
=  1:3:5,  and  1:4:6  =  1:2:4. 


334          XVII.   BENZENE  DERIVATIVES.      INTRODUCTION 

The  number  of  isomerides  is  considerably  increased  when 
the  three  substituents  are  not  similar,  e.g.  in  a  compound, 


ith  a  tetra-substituted  derivative,  C6H2X4,  where  all  four 
substituents  are  alike,  only  three  isomerides  are  possible, 
namely  those  corresponding  with  the  0-,  m-,  and  |?-di-deriva- 
tives  : 

X 


And  with  a  penta-substituted  derivative,  C6HX5,  only  one 
form  is  possible. 

The  number  of  isomerides  actually  found  in  each  case  is  in 
perfect  harmony  with  these  theoretical  deductions. 

The  ring  formula  for  benzene,  given  above,  represents  each 
carbon  atom  as  tervalent;  the  difficulty  of  accounting  for  the 
fourth  valency  can  be  overcome  in  several  ways. 

The  first  method,  suggested  by  KeJcuU,  was  to  suppose 
alternate  double  and  single  bonds  between  the  6  carbon 
atoms,  e.g.: 

CH 


This  formula  is  in  perfect  harmony  with  the  formation  of 
benzene  from  acetylene,  and  of  trimethyl-benzene  from  acetone. 
It  also  largely  accounts  for  the  formation  of  additive  com 
pounds  by  benzene  and  its  derivatives,  e.g. : 

CH*  CHC1 

1 

Hdl    »H  H( 


HC1 

Dihydro-benzeue        Tetrahydro-benzene       Benzene  hexachloride. 

Two  arguments  which  have  been  brought  forward  against 
this  formula  are — 


CONSTITUTION   OF  BENZENE  335 

(a)  Two  ortho-disubstituted  derivatives  should  be  possible, 

namely,  those  represented  by  the  formulae: 


In  formula  (I)  the  2  carbon  atoms  to  which  the  substituents 
are  attached  are  united  by  a  double  bond,  and  in  formula  (II) 
by  a  single  bond.  KekuU  has  suggested  that  the  single  and 
double  bonds  may  be  continually  changing,  so  that  positions 
2  and  6  are  really  symmetrical  with  respect  to  1. 

(b)  The  stability  of  benzene  towards  oxidizing  agents  has 
been  used  as  an  argument  against  such  a  formula  containing 
three  double  bonds  in  the  molecule.  Di-  and  tetrahydro- 
benzenes— obtained  by  the  reduction  of  benzene — which  con- 
tain respectively  two  and  one  double  bonds  in  their  molecules, 
are  readily  oxidized,  and  also  readily  yield  additive  compounds 
with  halogens.  It  has  been  suggested  that  the  peculiar  sym- 
metrical structure  of  the  benzene  molecule  may  account  for 
its  stability. 

(II)  A  second  method  of  accounting  for  the  fourth  valency 
of  each  carbon  atom  is  that  first  suggested  by  Armstrong,  and 
afterwards  developed  by  Baeyer: 


(IlA) 


It  represents  the  fourth  valency  of  each  carbon  atom  as 
directed  towards  the  centre  of  the  molecule,  where  the  6  are 
kept  in  equilibrium.  This  centric  formula  for  benzene  repre- 
sents a  method  of  linking  which  is  unknown  in  the  fatty 
series.  When  reduced  to  dihydro-benzene,  four  of  the  six 
centric  bonds  form  two  double  bonds. 


336 


XVII.    BENZENE   DERIVATIVES.      INTRODUCTION 


This  readily  accounts  for  the  great  difference  between  the 
chemical  properties  of  benzene  and  of  its  reduction  products. 

Various  other  formulae  have  been  suggested  for  benzene, 
e.g.  Ladenburg's  prism  formula,  Claus's  diagonal  formula,  and 
Dewar's  formula. 


(in) 


(IV) 


(V) 


Dewar 


Claus 


A  strong  objection  to  the  prism  formula  and  to  any  other 
three-dimension  space  formula  is  that  the  molecules  of  certain 
substituted  derivatives  would  be  perfectly  asymmetric,  and 
should  therefore  exist  in  optically  active  modifications.  No 
benzene  derivative  which  occurs  naturally  is  optically  active, 
and  attempts  to  resolve  substituted  benzene  derivatives,  e.g. 
C6H(OH)(C02H)(CH3)(C3H7)(N02),  nitrothymotic  acid,  have 
been  unsuccessful.  Rugheimer  (B.  1896,  29,  1967)  states, 
however,  that  he  has  obtained  w-methyl-jp-hydroxy-benzoic 
acid  in  an  optically  active  form. 

Other  objections  to  the  prism  formula  are  (a)  the  difficulty 
of  accounting  for  the  reduction  products  of  benzene,  and  (b) 
the  fact  that  when  benzene  is  oxidized  by  various  methods  no 
compound  is  met  with  which  contains  a  carbon  atom  attached 
to  3  other  carbon  atoms,  as  is  the  case  in  the  prism  formula. 

Researches  upon  the  constitution  of  benzene  and  its  deriva- 
tives by  Baeyer  (A.  245,  251,  256,  258,  269,  176),  and  upon 
similar  (and  also  nitrogen)  ring-systems  by  Bamberger  (A.  257, 
1),  have  shown  that  the  nature  of  the  groups  entering  the 
benzene  molecule  has  an  influence  upon  the  special  (fourth) 
linking  of  the  atoms ;  so  that  the  constitution  of  the  ring  in  all 
benzene  derivatives  is  not  to  be  taken  as  established  without 
further  investigation  because  a  particular  formula  applicable 
to  benzene  itself  has  been  arrived  at.  On  the  contrary, 
KeTcaU's  formula  (I)  might  suit  for  certain  compounds  (as 
has  been  proved  by  Biwyer  for  phloroglucinol  [B.  24,  2687]), 
and  formula  (IL\)  for  others. 

Compare  also  A.  274,  331;  279,  1;  B.  30,  2975;  A.  306. 
125;  Kauffmann,  Ahren's  Sammlung,  1907,  12,  79. 


ISOMERISM  OF  BENZENE  DERIVATIVES 


337 


METHODS  FOR  DETERMINING  WHICH  OF  THREE  ISO- 
MERIC  COMPOUNDS  IS  THE  ORTHO,  WHICH  MET  A, 
AND  WHICH  PARA. 

1.  A  method  worked  out  by  Korner  (1875)  for  the  three 
dibromobenzenes.  One  of  these  (a)  is  a  solid  melting  at  89°; 
a  second  (b)  is  a  liquid  which  boils  at  224°,  and  when  solidified 
melts  at  —1°;  and  the  third  (c)  is  a  liquid  boiling  at  219°  and 
melting  at  +1°.  When  further  brominated,  the  compound  a 
yields  only  one  tribromobenzene;  compound  b,  under  similar 
conditions,  yields  a  mixture  of  two  isomeric  tribromobenzenes; 
and  compound  c  a  mixture  of  three. 

Br  Br  Br 


From  a  glance  at  the  above  formulae,  it  is  obvious  (1)  that 
the  para-  or  l:4-compound  could  give  rise  to  only  one  tri- 
bromobenzene, (2)  that  the  ortho-  or  l:2-compound  could  give 
a  mixture  of  two  isomeric  tribromobenzenes,  and  (3)  that  the 
meta-  or  l:3-compound  could  give  a  mixture  of  three  isomeric 
tribromobenzenes. 

The  compound  melting  at  89°  is  therefore  ^-dibromobenzene, 
the  one  boiling  at  224°  is  the  ortho-,  and  the  one  boiling  at 
219°  and  melting  at  +1°  is  the  meta-compound. 

Incidentally,  this  gives  us  a  method  for  determining  which 
of  the  three  tribromobenzenes  is  the  adj.,  which  the  sym.,  and 
which  the  unsym.  A  glance  at  the  formulae  indicates  that  the 
sym.-tribromobenzene  is  the  one  which  is  formed  from  the 
m-dibromobenzene  only.  The  adj.  is  the  one  formed  from 
both  ortho-  and  meta-,  and  the  unsym.  is  the  one  which  is 
formed  from  ortho-,  meta-,  and  para-dibromobenzenes. 

Similar  results  are  obtained  by  examining  the  nitro-dibromo- 
benzenes  obtained  by  nitrating  the  dibromobenzenes. 

The  p-compound  yields  only  one  nitre-derivative;  the  0-com- 

(B480)  Y 


338          XVII.    BENZENE   DERIVATIVES.      INTRODUCTION 

pound  yields  two  nitro-derivatives;   the  ra-compound  yields 
three  nitro-derivatives : 


Br 


but  the  nitro-dibromobenzenes  thus  formed  are  all  different. 

Similar  methods  may  be  adopted  for  determining  the 
constitutions  of  the  three  diamino-benzenes,  C6H4(NH2)2,  by 
determining  from  how  many  of  the  six  diamino-benzoic  acids 
each  of  the  three  can  be  obtained  by  elimination  of  carbon 
dioxide. 

The  m-compound  is  the  one  which  is  formed  from  three 
distinct  acids,  the  ortho-  from  two,  and  the  para-  from  one 
only  (Griess). 

The  relationships  between  the  three  xylenes,  C6H4(CH3)2, 
and  the  six  nitro  -xylenes  are  exactly  analogous  to  those 
between  the  three  dibromobenzenes  and  their  six  nitro-deri- 
vatives. 

2.  When  the  constitution  of  several  groups  of  compounds, 
e.g.  the  dibromobenzenes,  the  xylenes,  and  the  diamino-ben- 
zenes have  been  settled,  then  the  constitutions  of  other  com- 
pounds can  be  determined  by  conversion  into  one  of  the 
compounds  of  known  constitution,  e.g.  the  dinitro-benzene 
which  yields  m-diamino-benzene  on  reduction  is  the  m-dinitro- 
compound,  or  the  acid  obtained  by  the  oxidation  of  o-xylene 
must  be  the  0-dicarboxylic  acid. 


This  constitution  is  confirmed  by  the  fact  that  this  acid 
is  the  only  one  of  the  three  ibomeric  benzene-dicarboxylic 


ISOMERISM  OF  BENZENE  DERIVATIVES  339 

acids  which  yields  an  inner  anhydride,  phthalic  anhydride, 
),  and  hence  the  two  C02H  groups  are  probably 


attached  to  two  adjacent  carbon  atoms. 

3.  The  constitution  of  certain  di-substituted  derivatives  is 
based  on  Ladenburg's  proof  (A.  179,  174)  of  the  equivalence 
of  the  three  unsubstituted  hydrogen  atoms  in  mesitylene, 
C6H3(CH3)3;  in  other  words,  on  the  fact  that  mesitylene  is 
sym.-trimethyl-benzene,  e.g.  the  constitution  of  w-xylene  is 
based  on  the  following  reactions:  — 


GEL 


C02 


Ladenburg's  proof  is  briefly  as  follows  :  —  Mesitylene  yields  a 
dinitro-derivative,  C6H(CH3)3(N02)2,  in  which  two  of  the  three 
nucleus  hydrogen  atoms  (a  and  b)  are  replaced  by  nitro-groups. 
From  this  we  get,  by  the  three  processes  of  reduction,  acety  • 
lation,  and  nitration,  a  dinitro-acetamino-mesitylene  : 

C6H(CH3)3(N02)(NH2)  —  C6H(CH3)3(N02)(NHAc) 

a  b 

—  C6(CH3)3(N02)2(NHAc), 

in  which  the  third  hydrogen  (c)  is  replaced  by  N02;  on  hydro- 
lysis, this  yields  C6(CH3)3(N02)2(NH2),  and  on  elimination  of 
the  amino-group,  C6H(CH3)3(N02)2,  a  olinitro-mesitylene,  which 
is  identical  with  the  original  dinitro-compound  started  with. 
Hence  two  of  the  hydrogen  atoms  (say  b  and  c)  are  similarly 
situated.  The  nitro-amino-mesitylene,  C6H(CH3)3(N02)(NH2), 

a     '       b 

in  which  the  nitro-group  is  in  position  a  and  the  amino-  in 
position  bt  yields  C6H2(CH3)3N02,  and  this,  when  reduced, 

a 

acety  lated,  nitrated,  and  hydrolysed: 

C6H2(CH3)3NH2  —  C6H2(CH3)3.NHAc 
a  a 


&  or  c  a        6  or  c 


a  nitro-amino-mesitylene  which  is  identical  with  the  original 
nitro-amino-mesitylene,  and  hence  the  position  a  is  similarly 
situated  to  either  b  or  c,  but  in  the  first  part  of  the  argument 
it  was  shown  that  b  =  c,  .*.  a  =  b  =  c. 


340          XVII.   BENZENE  DERIVATIVES.      INTRODUCTION 

Other  Types  of  Isomerism.  —  1.  In  addition  to  the  cases  of 
isomerism  dealt  with  in  the  preceding  pages  (isomerism  due  to 
the  positions  of  the  substituents  in  the  nucleus),  other  types  of 
isomerides  are  met  with.  A  frequent  example  is  the  isomerism 
of  a  compound  containing  a  substituent  in  the  nucleus  with  a 
compound  containing  the  same  substituent  in  the  side  chain; 
well-known  examples  are  C6H4C1  •  CH3  and  C6H5  •  CH2C1, 


and  C6H5-CH2.NH2.     Isomerism  of  this  type  is 

usually  accompanied   by  considerable  difference  in  chemical 
properties. 

2.  "  Side-chain  isomerism  "  is  the  name  given  when  the  iso- 
merism is  confined  to  the  side  chain,  e.g.  : 

C6H6.CH2.CH2.CH3    and    C6H5.CH(CH3)2 

Normal-  and       Isopropyl-benzene. 

Stereo-isomerism.  —  When  the  side  chain  contains  an  asym- 
metric carbon  atom,  e.g.  C6H5»CH(OH)(C02H),  mandelic  acid, 
stereo-isomerism  of  the  type  of  the  active  lactic  acids  is  met 
with.  Stereo-isomerism  of  the  type  of  the  crotonic  acids  is 
met  with  in  unsaturated  compounds  like  cinnamic  acid,  C6H5« 
CH:CH«C02H,  and  stereo-isomerism  analogous  to  that  de- 
scribed in  the  case  of  polymethylene  derivatives  is  met  with 
among  the  reduced  benzene  derivatives,  e.g.  di-,  tetra-,  and 
hexahydrophthalic  acid  (p.  466). 

OCCURRENCE  OF  THE  BENZENE  DERIVATIVES 

Many  benzene  derivatives  occur  in  nature,  e.g.  oil  of  bitter 
almonds,  benzoic  acid,  salicylic  acid,  and  hippuric  acid,  while 
others  are  obtained  from  the  destructive  distillation  of  organic 
substances,  especially  of  coal. 

The  destructive  distillation  of  coal  yields  (a)  gases  (illumi- 
nating gas);  (b)  an  aqueous  distillate  containing  ammonia  and 
its  salts,  &c.;  (c)  tar;  and  (d)  coke. 

The  various  fractions  obtained  by  distilling  coal-tar  contain  : 

(a)  Fatty  hydrocarbons  in  small  amount. 

(b)  Aromatic  hydrocarbons,  the  most  important  of  which 
are  the  following:  —  Benzene,  C6H6,  toluene,  CgH^CHg,  and 
many  homologues  of  benzene  containing  methyl  substituents, 
e.g.  mesitylene,  C6H3(CH3)3,  durene  and  isodurene,  C6H2(CH3)4. 
More    complex    hydrocarbons  :     cinnamene,    C6H5CH  :  CH2  ; 
naphthalene,  C10H8;  diphenyl,  C12H10;  acenaphthene,  C12H10; 


FORMATION  OF  BENZENE  DERIVATIVES  341 

fluorene,  C13H10;  anthracene,  C14H10;   phenanthrene,  CUH10; 
pyrene,  C16H10;  chrysene,  C18H12. 

(c)  Other   neutral   substances,  e.g.  alcohol   (in  very   small 
quantity),  benzonitrile,  cumarone,  CgHgO. 

(d)  Phenols:  e.g.  phenol  or  carbolic  acid,  C6H5OH;  o-,  m-, 
and  ^>-cresol,  CH3  •  C6H4  •  OH. 

(e)  Bases:  pyrrole,  C4H5N;  pyridine,  C5H5N,  and  its  homo- 
logues;  aniline,  CgH5»NH2;  quinoline,  C9H7N,  and  its  homo- 
logues;  acridine,  C13H9N.     (See  Schultz,  "Chemie  des  Stein- 
kohlentheers  ",  Braunschweig,  1886.) 

All  these  compounds  are  not  present  in  the  original  coal,  but 
are  formed  during  the  process  of  distillation.  The  compounds 
formed,  and  also  their  relative  amounts,  depend  on  numerous 
factors,  e.g.  nature  of  coal,  temperature  and  pressure  of  distil- 
lation, kind  of  retort  used,  &c. 

The  presence  of  the  hexahydro-compounds  of  benzene  and 
its  homologues  has  been  proved  in  most  natural  petroleums, 
especially  in  those  from  the  Caucasus  (J.  pr.  Ch.  (2)  45,  561; 
cf.  p.  41). 

FORMATION   OF  BENZENE  DERIVATIVES  FROM 
OPEN-CHAIN  COMPOUNDS 

The  benzene  derivatives  can  be  produced  from  the  fatty 
compounds  by  a  relatively  small  number  of  reactions  only. 

1.  Many  methane  derivatives,  e.g.  alcohol,  yield  a  mixture 
containing  a  large  number  of  the  derivatives  of  benzene  when 
their  vapours  are  led  through  red-hot  tubes.  Acetylene,  C2H2, 
polymerizes  at  a  low  red  heat  to  benzene,  C6H6  (Berthelot): 

CH  CH 

HC         CH  HC      CH 

HC         CH  HC      CH 


V 

In  an  analogous  manner  allylena  CH3'C':CH,  yields  mesity- 
lene  or  1:3:5  trimethyl-benzene,  C6H3(CH3)3,  when  distilled 
with  dilute  sulphuric  acid,  while  crotonylene,  CH3»C:C»CH3, 
yields  hexamethyl  -benzene,  C6(CH3)6;  bromo-  acetylene  and 
iodo-acetylene  polymerize  to  s-tribromo-  and  ^tn-iodo-benzene 
when  exposed  to  light;  propiolic  acid,  CH*:C'C02H,  poly- 
merizes to  trimesic  acid,  C6H3(C02H)3. 


342         XVII.   BENZENE  DERIVATIVES.      INTRODUCTION 

2.  Ketones  condense  to   benzene  hydrocarbons  when  dis- 
tilled with  dilute  sulphuric  acid,  e.g.  acetone  yields  mesitylene 
(Kane,  1838)  and  methylethyl  ketone,  triethyl-benzene: 

CH3  CH3 

C(C»  C 

(H2)CH          CH(H)2  HC      CH 

|  -*  I'    1          +3H20. 

CH3.C(0)        0(0). CH3  CH3-C      CJ.CH3 

(H2)CH  C 

3  mols.  Acetone  H 

Mesitylene 

3.  Certain  1 : 2-diketones,  aldehyde  acids,  and  keto-aldehydes 
are  transformed  in  an  analogous  manner  into  benzene  deri- 
vatives   by    suitable    "condensing"   agents;    diacetyl,    CH3« 
CO'CO'CH3,  is   transformed   by   alkalis   into   xylo-quinone, 
C6H202(CH3)2  (B.  21,  1411),  and  ethyl  /3-hydroxyacrylate  into 
the  ethyl  ester  of  trimesic  acid  (B.  20,  2930). 

4.  Certain  1 : 5  diketones  react  with  hydrochloric  acid,  yield- 
ing reduced  benzene  derivatives,  which  can  readily  be  trans- 
formed into  benzene  derivatives,  e.g.  ethylidene-diacetoacetic 
ester  (from  acetaldehyde  and  acetoacetic  ester)  yields  dimethyl- 

QQ QTT 

cyclo-hexenone,    CH<Tr<\T    XtrOOHMe,    the   dibromide   of 

^L/ivie-urig 

which  is  converted  into  sym.-xylenol, 
(Knoevenagel). 

5.  By  the  action  of  methylene  iodide  upon  the  sodium  com- 
pound of  ethyl  pentane-tetracarboxylate  and  subsequent  hy- 
drolysis, hexahydro-isophthalic  acid  is  formed  (W.  H.  Perkln, 
jun.,  J.  C.  S.  1891,  59,  798): 

CH9  CH, 


2C      CH.' 


H2C      C(C02Et)2  H2C      CH-C02H 

|        \N         +CH2I2      —  |        | 

H2C    Na   1  H2C      CH2 

)(C02Et)2  CH.C02H 

Sodium  compound  of  ethyl  Hexahydro-isophthalic 

pentane-tetracarboxylate  acid. 

6.'  By  the  action  of  sodium  upon  ethyl  succinate  (Herrmann, 
A.  211,  306;  B.  16,  1411),  or  upon  ethyl  bromo-acetoacetate 
(Duisberg),  ethyl  snccinylo- succinate,  "ethyl  diketo-hexa- 


DECOMPOSITION  Of  BENZENE  COMPOUNDS  343 

methylene-dicarboxylate ",  is  obtained,  and  is  readily  trans- 
formed into  ethyl  dihydroxy-terephthalate  and  then  into  quinol: 

EtO;CO  CO 

CO2Et.HC;H        j        CH2  C02Et-HC      CH2 

H2C        i H;CH.CO2Et  H2C      CH'COaEt 

COiOEt  CO 

2  mols.  Ethyl  succinate  Ethyl  succinylo-succinate. 

7.  When  ethyl  sodio-malonate,  CHNa(C02Et)2,  is  heated, 
ethyl  phloroglucinol-dicarboxylate  is  formed,  and  this  on  hy- 
drolysis yields  phloroglucinol.     (Cf.  p.  420.) 

8.  Hexyl  iodide,  C6H13I,  is  converted  into  hexachloro-ben- 
zene,  C6C16,  when  heated  with  IC13,  and  into  hexabromo-ben- 
zene,  C6Br6,  by  bromine  at  260°;  the  latter  compound  can  also 
be  obtained  by  heating  CBr,  to  300°. 

9.  Mellitic  acid,  C6(C02H)6,  is  produced  by  the  oxidation 
of  graphite  or  lignite  by  means  of  KMnO4. 

10.  Potassium  carboxide,  which  is  formed  by  the  action  of 
carbon  monoxide  upon  potassium,  is  the  potassium  compound 
of  hexahydroxy-benzene,  C6(OH)6. 

THE  CONVERSE  TRANSFORMATION  OF  BENZENE  DERI- 
VATIVES INTO  FATTY  COMPOUNDS 

1.  When  the  vapour  of  benzene  is  passed  through  a  red-hot 
tube  it  is  partially  decomposed  into  acetylene. 

2.  Benzene  is  oxidized  by  chloric  acid  to  "  trichloro-pheno- 
malic  acid",  i.e.  /3-trichloraceto-acrylic   acid,  CC18'CO«CH: 
CH.C02H  (KekuU  and  Strecker,  A.  223,  170). 

When  chlorine  is  allowed  to  act  upon  phenol  in  alkaline 
solution,  the  benzene  ring  is  broken,  and  the  acids,  C6H6CloO4, 
C6H5C104,  &c.,  are  produced  (Hantzsch,  B.  20,  2780).  Catechol, 
resorcinol,  and  phloroglucinol  are  also  ultimately  converted 
into  fatty  compounds  by  treatment  with  chlorine  and  the  sub- 
sequent action  of  alkalis,  e.g.  resorcinol  (m-dihydroxybenzene) 
yields  dichloro-maleic  acid  (B.  1894, 27,  3364).  Bromine,  acting 
upon  bromanilic  acid,  yields  perbromo-acetone,  CBr8«CO»CBr3. 

3.  Nitrous  acid  converts  catechol  into  dihydroxy-tartaric 
acid  (see  p.  260),  while  permanganate  of  potash,  acting  upon 
phenol,  gives  rise  to  inactive  tartaric  acid  and  oxalic  acid 
(Dobner,  B.  24,  1753). 


344  XVIII.  BENZENE  HYDROCARBONS 

4.  Oxidizing   agents  which  are  capable  of   rupturing   the 
benzene  ring  yield,   as  a  rule,   carbonic,  formic,  and  acetic 
acids. 

5.  The   hexahydro-  benzenes   are   transformed   into  hydro- 
carbons of  the  methane  series  when  heated  with  hydriodic 
acid  at  280°  (Berthelot,  A.  278,   88;  302,  5).     This  decom- 
position appears,  however,  to  be  very  difficult  of  accomplish- 
ment. 

6.  When  reduced  with  metallic  sodium  and  amyl  alcohol, 
0-hydroxy-benzoic  acid  is  converted  into  pimelic  acid: 


CH 


XVIII.    BENZENE    HYDROCARBONS 
A.  Homologues  of  Benzene, 


The  benzene  hydrocarbons  are  for  the  most  part  colourless 
liquids,  insoluble  in  water,  but  readily  soluble  in  alcohol  and 
ether  (durene  and  penta-  and  hexamethyl-benzenes  are  crys- 
talline). They  distil  without  decomposition,  possess  a  peculiar 
and  sometimes  pleasant  ethereal  odour,  and  burn  with  a  very 
smoky  flame.  Many,  especially  benzene  and  its  methyl  deriva- 
tives, occur  in  the  lower  fractions  from  coal-tar;  others  are 
prepared  synthetically  by  Fittig's  or  Friedel-Crafts'  methods. 

Modes  of  Formation.  —  1.  Fittig's  Synthesis.  —  By  treating  a 
mixture  of  a  brominated  benzene  hydrocarbon  and  an  alkyl 
iodide  or  bromide  with  sodium  in  the  presence  of  dry  ether 
(A.  131,  303): 

Br  +  CH3I  +2Na  ==  C6H6.CH3     -f  Nal  +  NaBr; 


66  3  ==     66.3     -       a  r; 

C6H4Br(02H5)  +  C2H6I  +  2Na  =  C6H4(C2H5)2  -f  Nal  +  NaBr. 


BENZENE  AND  ITS   HOMOLOGUES 


345 


346  XVIII.   BENZENE  HYDROCARBONS 

Jannasch  synthesised  ^?-xylene,  durene,  and  isodurene  by  this 
method. 

2.  Friedel^  and  Crafts1  Synthesis  (1877).— By  the  action  of 
alkyl    chlorides   (bromides   or    iodides)   on    aromatic    hydro- 
carbons  in   the   presence    of    anhydrous   aluminic   chloride, 
(A1C13): 

C6H6  +  CH3C1     =  C6H6.CH3   +HC1; 
CflH6  +  2CH3C1  =  C6H4(CH3)2  +  2HC1,  &c. 

This  reaction  is,  like  the  preceding  one,  capable  of  very 
wide  application;  by  means  of  it  all  the  hydrogen  atoms  in 
benzene  can  be  gradually  replaced  by  methyl.  The  best 
yields  are  often  obtained  by  the  addition  of  carbon  bisulphide, 
which  serves  as  a  diluent,  and  also  prevents  the  temperature 
rising  to  any  appreciable  extent,  and  thus  largely  avoids  the 
decomposing  or  differentiating  action  of  the  chloride  on  the 
homologues  first  formed.  At  higher  temperatures,  for  ex- 
ample, C6H5'CH3  would  be  transformed  to  a  large  extent 
into  C6H6  and  C6H4(CH3)2  (B.  1894,  27,  1606,  3235). 

Zinc  and  ferric  chlorides  (Nencki,  B.  1899,  32,  2414)  act  in 
the  same  way  as  chloride  of  aluminium,  while  ethyl  chloride 
and  other  haloid  compounds,  such  as  chloroform  and  acid 
chlorides,  may  replace  methyl  chloride.  (See  respectively 
triphenyl-methane  and  the  ketones;  cf.  also  B.  14,  2624;  16, 
1744;  Ann.  de  chim.  et  phys.  [6]  \  419;  B.  30,  1766.)  The 
metallic  chloride  forms  additive  compounds  with  the  acyl 
chloride  or  alkyl  derivative,  e.g.  CEL  •  COC1,  A1C13,  and  also 
with  the  condensation  product,  e.g.  C6H5  •  CO  •  CH3,  A1C13  (Per- 
rier,  B.  1900,  33,  815).  The  reaction  is  a  unimolecular  one, 
except  when  an  excess  of  A1C13  is  used. 

For  a  summary  of  the  Friedel- Crafts'  reaction,  see  Steele, 
J.  C.  S.  1903,  1470. 

Alcohols  also,  like  their  haloid  esters,  are  capable  of  react- 
ing in  an  analogous  manner  in  presence  of  ZnCl2 : 

C6H6  +  C4H9OH  =  C6H6.C4H9  +  H2O. 

3.  A  method  of  formation  somewhat  analogous  to  the  Fittig 
synthesis  is  the  action  of  alkyl  iodides  or  methyl  sulphate  on 
organo-magnesium  haloids  (Grignard's  compounds)  in  toluene 
solution  (Houben,  B.  1903,  36,  3083;  1904,  37,  488;  Werner, 
ibid.,  2116,  3618): 

CH3.C6H4.MgBr  +  C2H6Br  =  CH3.C6H4.C2H6  +  MgBr2. 


FORMATION   Of  BENZENE   HYDROCARBONS  347 

4.  The  benzene  hydrocarbons  are  formed  when  their  carb- 
oxylic  acids  are  distilled  with  soda-lime: 

C6H5.C02H  =  C6H6  +  C02; 
CH3.C6H4.C02H  =  C6H66.CH34-002. 

5.  From  sulphonic  acids  (p.  402)  by  the  elimination  of  the 
S03H  group: 

C6H3(CH3)2S03H  +  H20  =  C6H4(CH3)2-t-H2S04. 

This  reaction  can  be  effected  by  dry  distillation,  by  heating 
with  concentrated  hydrochloric  acid  to  180°,  by  distillation  of 
the  ammonium  salt  (Caro),  or  by  treatment  with  superheated 
steam,  e.g.,  in  presence  of  concentrated  sulphuric  acid  (Arm- 
strong, W.  Kelbe);  also  by  heating  with  concentrated  phosphoric 
acid  (B.  22,  Kef.  577). 

6.  From  the  amino-compounds  by  transforming  these  into 
diazonium-compounds  (p.  387),  and  boiling  the  latter  with  ab- 
solute alcohol  or  with  an  alkali  stannite  solution  (B.  22,  587). 
Griess  reaction. 

7.  By  distillation  of  the  phenols  (or  ketones)  with  zinc  dust. 
homers  and  Constitution. — The  table  given  on  p.  345  shows 

that  the  benzene  hydrocarbons,  from  C8H10  on,  exist  in  many 
isomeric  modifications;  thus,  isomeric  with  the  three  xylenes 
we  have  ethyl-benzene,  with  the  three  trimethyl-benzenes 
the  three  methylethyl-benzenes  and  the  two  propyl-benzenes, 
with  durene,  isodurene,  cymene,  &c. 

The  constitution  of  these  hydrocarbons  follows  very  simply 
from  their  modes  of  formation.  A  hydrocarbon  C]0H14,  for 
instance,  which  is  obtained  from  benzene  and  methyl  chloride 
by  the  Friedel-Crafts'  reaction,  can  only  be  a  tetramethyl-ben- 
zene;  another  of  the  same  molecular  formula  C10H14,  which  has 
been  prepared  from  bromo-benzene,  butyl  bromide  and  sodium, 
must  be  a  butyl-benzene ;  while  a  third,  from  j9-bromo-toluene, 
normal  propyl  iodide  and  sodium,  must  be  a  jp-propyl-toluene 
(p-methyl-7i-propyl-benzene),  &c.  The  synthesis  therefore  de- 
termines the  constitution. 

The  groups  CH3,  C2H5,  &c.,  which  replace  hydrogen  in 
benzene,  are  termed  "side  chains". 

When  oxidized,  the  hydrocarbons  yield  a  benzene-mono-, 
di-,  or  tri-,  <fec.,  carboxylic  acid,  e.g.  benzoic  acid,  C6H5»C02H, 
0-,  m-,  £>-phthalic  acid,  C6H4(C02H)2,  according  to  the  number 
of  side  chains  present  in  the  hydrocarbon;  and  a  further  proof 
of  the  constitution  of  the  compound  is  thus  afforded. 


348  XVIII.   BENZENE  HYDROCARBONS 

If,  for  example,  a  hydrocarbon  C9H12  yields  a  benzene-tri- 
carboxylic  acid,  C6H3(C02H)3,  upon  oxidation,  it  must  contain 
three  side  chains,  i.e.  must  be  a  trimethyl-benzene;  should  a 
phthalic  acid,  on  the  other  hand,  result,  then  it  can  only  be 
an  ethyl-toluene.  Since  cymene  yields  p-  (or  tere-)  phthalic 
acid,  C6H4(C02H)2,  on  oxidation,  its  two  side  chains  must  be 
in  the  ^-position  towards  one  another. 

The  respective  isomers  resemble  each  other  closely  in 
physical  properties,  their  boiling-points,  for  example,  lying 
very  near  together.  The  ortho-derivatives  often  boil  at  about 
5°,  and  the  meta-  at  about  1°  higher  than  the  para-compounds; 
the  boiling-point  rises  with  an  increasing  number  of  methyl 
groups.  (Of.  B.  19,  2513.) 

Behaviour. — 1.  The  benzene  hydrocarbons  are,  as  a  rule, 
readily  nitrated  and  sulphonated,  mono-,  di-,  and  even  tri- 
derivatives  being  all  usually  capable  of  preparation,  according 
to  the  conditions.  As  a  rule,  it  is  only  the  hydrogen  atoms 
of  the  benzene  nucleus  which  are  replaced,  the  side  chains 
reacting  as  paraffin  residues.  Hexamethyl-benzene  can  thus 
neither  be  nitrated  nor  sulphonated.  Exceptions  to  this 
generalization  are  met  with,  e.g.  mesitylene  yields  a  nitro- 
derivative,  C6H3(CH3)2.CH2.N02. 

2.  Oxidation. — Benzene  itself  is  not  readily  oxidized;  per- 
manganate of  potash  converts  it  slowly  into  formic  and  oxalic 
acids,  some  benzoic  acid  and  phthalic  acid  being  produced  at 
the  same  time.     These  doubtless  result  from  some  previously 
formed  diphenyl. 

The  homologues  of  benzene,  on  the  other  hand,  are  readily 
oxidized  to  carboxylic  acids,  the  benzene  nucleus  remaining 
unaltered,  and  each  side  chain — no  matter  how  many  carbon 
atoms  it  may  contain — being  converted,  as  a  rule,  into  carb- 
oxyl. 

Nitric  acid  allows  of  a  successive  and  often  a  partial  oxi- 
dation of  individual  side  chains,  chromic  acid  mixture  (K2Cr207 
+  H2S04)  acts  more  energetically,  converting  all  the  side  chains 
in  the  p-  and  m-compounds  into  carboxyl,  and  completely 
destroying  the  o-compounds.  The  latter  may  be  oxidized  to 
the  corresponding  carboxylic  acids  by  KMn04. 

When  a  hydrocarbon  is  selectively  oxidized,  the  longest  side 
chain,  as  a  rule,  is  most  readily  oxidized;  thus  C3H7»C6H4- 
CH3  yields  first  C02H .  C6H4 .  CH3,  and  then  C6H4(C02H)2. 

3.  Reduction. — The  benzene  hydrocarbons  and  most  of  their 
derivatives  are  capable  of  taking  up  six  atoms  of  hydrogen. 


REDUCED  BENZENE  DERIVATIVES  349 

Benzene  itself  is  only  converted  into  hexahydro-benzene,  C6H12, 
with  difficulty,  but  toluene,  xylene,  and  mesitylene  combine 
with  hydrogen  more  easily  when  they  are  heated  with  phos- 
phonium  iodide,  PH4I,  at  a  rather  high  temperature,  the  com- 
pounds C7H8  •  H2,  C8H10  •  H4,  and  C9H12  •  H6  being  formed.  The 
two  former  can  then  be  made  to  take  up  more  hydrogen  by 
energetic  reaction. 

An  interesting  method  of  formation  of  C6H12  is  by  the  action 
of  freshly  reduced  nickel  on  a  mixture  of  hydrogen  and  ben- 
zene or  its  homologues  at  moderate  temperatures. 

Hexahydro-benzene  and  its  analogues,  C^H^,  are  colourless 
liquids  insoluble  in  water,  and  of  somewhat  lower  boiling-point 
than  their  mother  compounds,  into  which  they  can  be  readily 
retransformed  by  oxidation,  either  by  heating  with  sulphur  or 
by  means  of  fuming  nitric  acid,  nitration  also  taking  place  in 
the  latter  case;  e.g.  hexahydro-benzene  yields  nitro-derivatives 
of  benzene.  They  are  found  in  petroleum,  especially  in  that 
from  the  Caucasus  (Eeilstein,  Kurbatow),  and  differ  from  the 
isomeric  defines  by  being  insoluble  in  sulphuric  acid,  and  by 
not  forming  additive  products  with  bromine  (cf.  B.  20,  1850; 
A.  234,  89;  301,  154). 

They  are  identical  with  hexamethylene  and  its  derivatives, 
and  react  as  saturated  compounds.  The  partially  reduced 
benzene  derivatives,  on  the  other  hand,  behave  more  like 
olefines. 

The  dihydro-benzenes,  C6H8,  readily  combine  with  two  or 
four  atoms  of  bromine,  and  are  readily  oxidized  by  alkaline 
permanganate,  as  .might  be  inferred  from  the  presence  of 
double  bonds  in  the  molecule.  Two  isomeric  compounds, 
A  1 : 3-dihydro-benzene  and  A  1 : 4-dihydro-benzene,  are  known: 


L2 

Cyclohexa-1 : 4-diene 


Tetrahydro-benzene,  ,  which  exists  in  one  form 

H2k/H2 

H2 

Cyclohexene 


350  XVIII.   BENZENE  HYDROCARBONS 

only,  is  readily  oxidized,  combines  with  two  atoms  of  chlorine 
and  bromine  or  with  a  molecule  of  hypochlorous  acid.  All  are 
colourless,  volatile  liquids. 

4.  Behaviour  with  Halogens. — Chlorine   and   bromine   react 
differently,  according  to  the  conditions.     In  direct  sunlight 
they  yield  with  benzene  the  additive  products  C6H6C16  and 
C6H6Br6,  while  in  diffused  daylight,  especially  in  presence  of  a 
little  iodine,  SbCl3  or  MoCl5,  they  give  rise  to  the  substitution 
products  C6H5C1,  C6H6Br,  &c.     (For  further  details,  and  for 
substitution  by  iodine,  see  pp.  57  and  356.) 

5.  Chromium  oxychloride,  Cr02Cl2,  converts  the  methylated 
benzene  hydrocarbons  into  aromatic  aldehydes  (p.  423;  cf.  B. 
23,  1070).     (Etard's  reaction.) 

6.  The  numerous  "  condensations  "  which  benzene,  &c.,  can 
undergo  with  oxygenated  compounds  in  presence  of  ZnCl2, 
P4010,  or  H2S04,  and  with  chlorinated  compounds  in  presence 
of  A1C13,  are  of  great  interest;  thus  benzene  yields  diphenyl- 
ethane  with  aldehyde  and  sulphuric  acid,  and  benzophenone 
with  benzoic  acid  and  phosphorus  pentoxide. 

7.  In  presence  of  aluminic  chloride,  oxygen  can  be  intro- 
duced into  benzene,  yielding  phenol;  sulphur,  yielding  phenyl 
sulphide;   ethylene,  yielding  ethyl-benzene;   carbon  dioxide, 
yielding  benzoic  acid. 

Benzene,  C6H6,  was  discovered  by  Faraday  in  1825,  and 
detected  in  coal-tar  by  Hofmann  in  1845.  It  is  obtained  from 
the  portion  of  coal-tar  which  boils  at  80°-85°  by  fractionating 
or  freezing.  It  may  be  prepared  chemically  pure  by  distilling 
a  mixture  of  benzoic  acid  and  lime.  The  ordinary  benzene  of 
commerce  usually  contains  thiophene,  and  thus  gives  a  char- 
acteristic deep-blue  coloration  when  shaken  with  a  solution  of 
isatin  in  concentrated  sulphuric  acid;  but  it  may  be  freed 
from  the  impurity  by  repeated  shaking  with  small  quantities  of 
sulphuric  acid,  which  converts  the  thiophene  into  a  sulphonic 
acid.  It  burns  with  a  luminous  smoky  flame,  and  is  a  good 
solvent  for  resins,  fats,  iodine,  sulphur,  phosphorus,  &c.  When 
its  vapour  is  led  through  a  red-hot  tube,  diphenyl  is  obtained. 

C7H8.—  Toluene,  C6H5-CH3.  Discovered  in  1837.  Formation: 
by  the  dry  distillation  of  balsam  of  Tolu  and  of  many  resins. 
Synthesis  according  to  Fittig  (see  above).  Preparation-,  from 
coal-tar,  in  which  it  is  found  accompanied  by  thio-tolene. 
Toluene  is  very  similar  to  benzene.  It  boils  at  110°,  and  is 
still  liquid  at  —28°.  Cr02Cl2  converts  it  into  benzaldehyde, 
and  HN03  or  Cr08  into  benzoic  acid. 


XYLENES  351 

C8H10. — (a)  o-,  m-,  and  ^-Dimethyl-benzenes  or  Xylenes, 
C6H4(CH3)2. — The  xylene  of  coal-tar  consists  of  a  mixture  of 
the  three  isomers,  m-xylene  being  present  to  the  extent  of  70 
to  85  per  cent.  These  cannot  be  separated  from  one  another 
by  fractional  distillation.  wi-Xylene  is  more  slowly  oxidized 
by  dilute  nitric  acid  than  its  isomers,  and  can  thus  be  obtained 
with  relative  ease. 

For  the  separation  of  these  isomers  by  means  of  H2S04  see 
B.  10,  1010;  14,  2625;  17,  444;  25,  Kef.  315;  and  for  their 
recognition  see  B.  19,  2513.  Benzene  and  toluene  yield  chiefly 
ortho-,  together  with  a  little  para-xylene,  when  subjected  to 
the  Friedel-Crafts  synthesis  (B.  14,  2627). 

1.  o-  Xylene,   which   can   be   prepared   synthetically  from 
0-bromo-toluene,  methyl  iodide,  and  sodium,  is  oxidized  to 
carbonic  acid  by  chromic  acid  mixture,  and  to  0-toluic  acid, 
C6H4(CH3)C02H,   by   dilute    nitric    acid;    it    is   difficult   to 
nitrate. 

2.  m-Xylene  or  iso-xylene  can  also  be  prepared  from  mesity- 
lene,  C6H3(CH3)3,  [1:3:5],  by  oxidation  to  mesitylenic  acid, 
CgH3(CH3)2C02H,    and    subsequent    distillation    with    lime. 
Dilute  nitric  acid  only  oxidizes  it  at  a  temperature  of  120°, 
while  chromic  acid  mixture  converts  it  into  isophthalic  acid, 
C6H4(C02H)2.      It  yields  tetra-  and  hexahydro-  derivatives, 
C8H14  and  C8H16;  the  latter  is  present  in  Caucasian  petroleum, 
and  boils  at  11 9°. 

3.  ^-Xylene   is  prepared  from  j?-bromo-toluene,  or  better, 
;?-dibromo-benzene,  methyl  iodide,  and  sodium  (B.  10,  1356; 
B.   17,  444).     M.-pt.  13°.     Dilute  nitric  acid  oxidizes  it  to 
0-toluic    acid,     C,H4(  GIL  )C02H,    and    terephthalic    acid, 
C6H4(C02H)2. 

Dihydro-^-xylene  can  be  prepared  from  ethyl  succinylo-suc- 
cinate.  Liquid;  b.-pt.  133°.  It  has  an  odour  of  turpentine,  and 
is  closely  related  to  the  terpenes.  (Cf.  Baeyer,  B.  25,  2122.) 

Jb)  Ethyl-benzene,   C6H5.02H5,  is  obtained  from   C6H5Br 
CoH5Br  by  the  Fittig  reaction;   from  cinnamene,  CJ35 
CH:CH2,  on  reduction  with  HI;  and  from  C6H6  and  C2H5C1 
by  the  Friedel-Crafts  reaction.     It  is  found  in  small  quantity 
in  the  xylene  from  tar,  and  when  oxidized  yields  benzoic  acid. 
C9H12. — (a)  Trimethyl-benzenes, — 1.  Mesitylene,  l:3:5-tfn- 
methyl-benzene,    C6H3(CH3)3. — This    is   contained   in   coal-tar 
along  with  the  two  other  isomeric  trimethyl-benzenes  ("tar- 
cumene "),  and  can  be  synthesised  from  acetone  or  allylene. 
It  is  a  liquid  of  agreeable  odour.     Nitric  acid  oxidizes  the 


352  XVIII.    BENZENE   HYDROCARBONS 

side  chains  one  by  one,  while  chromic  acid  mixture  decom- 
poses it  completely.     (For  constitution,  see  p.  339.) 

2.  Pseudo-cumene,  l-.Z-A-trimethyl-benzene,  is  separated  from 
mesitylene,  not  by  fractional  distillation,  but  by  taking  ad- 
vantage of  the  sparing  solubility  of  pseudo-cumene-sulphonic 
acid  (B.  9,  258).     Its  constitution  follows  from  its  formation 
from  bromo-j^-xylene  [1:4:2],  and  also  from  bromo-w-xylene 
[1:3:4],  by  the  Fittig  reaction.     Nitric  acid  oxidizes  the  side 
chains  successively. 

3.  Hemellithene,  l:2:3-trimethyll)enzene  (see  B.  15,  1853),  is 
present  in  coal-tar  (B.  20,  903). 

(b)  Pr opyl- benzenes,— 1.  w-Propyl- benzene,  C6H5.CH2- 
CH2'CH3,  is  obtained  from  bromo-benzene  and  normal  propyl 
iodide  by  the  Fittig  reaction,  and  also  from  benzyl  chloride, 
C6H5.CH2C1,  and  zinc  ethyl. 

2.  Isopropyl-benzene  or  Cumene,  CgH5«CH(CH3)2,  is  pro- 
duced by  the  distillation  of  cumic  acid,  C6H4(C3Hf)(C02H), 
with  lime;  from  benzene  and  iso-  or  normal  propyl  iodide  by 
means  of  A1C13,  in  the  latter  case  with  molecular  rearrange- 
ment (p.  132);  and  from  benzylidene  chloride,  C6H««CHC12, 
and  zinc  methyl,  this  last  method  furnishing  proof  of  its  con- 
stitution. On  oxidation,  both  n-  and  iso-compounds  yield  ben- 
zoic  acid. 

Cj0H14. — (a)  Durene,  1:2:4:5-  or  s-tetramethyl-benzene, 
C6H2(CH3)4,  has  been  found  in  coal-tar,  and  can  be  prepared 
from  toluene  and  methyl  chloride  by  the  Friedel-Crafts  reaction, 
or  from  dibromo-m-xylene  (from  coal-tar  xylene),  methyl  iodide, 
and  sodium  (A.  216,  200).  It  is  a  solid,  and  possesses  a  camphor- 
like  odour.  (For  its  constitution  see  B.  11,  31.)  Both  of  its 
isomers  are  known. 

(b)  Methyl-propyl-benzenes,  C6H4(CH3)C3H7.— The  most 
important  of  these  is  cymene  or  isopropyl-p-methyl-benzene. 
It  is  found  in  Eoman  cummin  oil  (Cuminum  cyminum),  in 
eucalyptus  oil,  &c.,  and  is  formed  when  camphor  is  heated 
with  PgSg,  or  better,  P4010,  also  when  oil  of  turpentine  is 
heated  with  iodine,  &c.  It  has  been  synthetically  prepared 
from  ^7-bromo-isopropyl-benzene,  methyl  iodide,  and  sodium; 
and  also  from  j9-bromo-toluene,  n-propyl  iodide,  and  sodium, 
the  %-propyl-  changing  here  into  the  isopropyl  group.  It  is  a 
liquid  of  agreeable  odour. 

Cymene  was  formerly  regarded  as  7i0maZ-propyl-^>-methyl- 
benzene,  but  its  synthesis  from  ^?-brom-w0-propyl-benzene, 
methyl  iodide,  and  sodium  established  its  constitution  as  an 


UNSATURATED  BENZENE  HYDROCARBONS      353 

isopropyl  derivative  (cf.  JVidman,  B.  24,  439).  When  oxidized, 
it  yields  either  ^7-toluic  acid,  terephthalic  acid,  cumic  acid,  or 
/>-tolyl-methyl-ketone,  according  to  the  conditions. 

C12H18. — Hexamethyl- benzene,  Mellitene,  C6(CH3)6,  crys- 
tallizes in  prisms  or  plates  which  melt  at  164°.  It  can  neither 
be  sulphonated  nor  nitrated  (see  p.  347).  KMn04  oxidizes  it 
to  mellitic  acid,  C6(C02H)6. 

B.  Unsaturated  Benzene  Hydrocarbons 

The  benzene  hydrocarbons  containing  less  hydrogen  comport 
themselves,  on  the  one  hand,  like  benzene  itself,  and  on  the 
other  like  the  un saturated  hydrocarbons  of  the  fatty  series, 
combining  readily  with  hydrogen,  halogen,  halogen  hydride, 
&c.  They  are  derived  from  the  olefines  or  acetylenes  by  the 
exchange  of  H  for  C6H5,  thus:  C6H5'CH:CH2,  cinnamene, 
styrene,  or  phenyl-ethylene;  C6H5.C|CH,  phenyl-acetylene. 
They  are  formed  by  the  elimination  of  C02  from  the  corre- 
sponding acids,  by  the  elimination  of  HBr  from  compounds  of 
the  type  C6H5  •  CH2  •  CH2Br,  and  by  the  elimination  of  water 
from  certain  secondary  and  tertiary  alcohols  (C.  R.  1901,  132, 
1182). 

Cinnamene,  C6H5-CH:CH2,  occurs  along  with  other  com- 
pounds in  storax  (Styrax  officinalis),  in  the  juice  of  the  bark  of 
Liquidambar  orientate,  and  in  coal-tar  (being  in  this  last  case 
probably  a  degradation  product  of  certain  acids).  It  is  formed 
when  cinnamic  acid  is  slowly  distilled  or  heated  with  water  to 
200°  (B.  1890,  23,  3269):  C6H5 •  CH : CH •  :COO;H. 

It  is  also  obtained  when  benzene  vapour  and  ethylene  are 
passed  through  a  red-hot  tube,  or  when  a-bromo-ethyl-benzene, 
C6H5'CH2'CH2Br  (by  action  of  bromine  on  ethyl-benzene),  is 
heated.  It  is  a  liquid,  has  a  characteristic  odour,  and  boils  at 
140°.  It  changes  on  keeping  into  the  polymeric  meta-styrene, 
an  amorphous  transparent  mass,  and  yields  ethyl-benzene  when 
heated  with  hydriodic  acid.  Addition  of  HBr  converts  it  into 
a-bromo-ethyl-benzene,  C6H5  •  CH2  •  CH2Br.  By  the  conden- 
sation of  styrene  with  toluene,  in  presence  of  concentrated 
sulphuric  acid,  and  on  subsequent  superheating,  anthracene  is 
formed  (Kramer,  Spilker,  B.  23,  3169). 

Phenyl-acetylene,  CyHg.CjCH,  is  produced  by  the  separa- 
tion of  C02  from  phenyl-propiolic  acid. 

It  is  a  pleasant-smelling  liquid  boiling  at  142°,  and  as  an 
acetylene  derivative  yields  white  and  pale-yellow  explosive 

(B4SO)  Z 


354  XIX.  HALOGEN  DERIVATIVES 

metallic  compounds  with  solutions  of  silver  and  cuprous 
oxides.  It  combines  with  water  to  aceto-phenone,  C6H6»CO» 
CH3,  when  it  is  dissolved  in  sulphuric  acid,  and  the  solution 
is  diluted  with  water,  or  when  heated  with  water  to  300°. 


XIX.  HALOGEN  DERIVATIVES 

SUMMAKY 

Cl  Br                         I 

M.-p.      B.-p.  M.-p.  B.-p.  M.-p.  B.-p. 

C6H6C1  ...............     -45°     132°  -31°  157°  -30°  188° 

C6H4C12  o    .........      liq.       179°  -1°  224°  +27°  286° 

m  .........      liq.       172°  liq.  220°  +40°  285° 

p   .........     +56°     173°  +87°  219°  +129°  285° 

CH3.CflH4Clo    ...     —34°     159°  -26°  181°  liq.  211° 

m  ...     —48°     162°  —40°  184°  liq.  204° 

p   ...    +7'4°     162°  28°  185'  +35°  211'5° 

C6H6.CH2C1  ........     -48°    175°  ...  198°  +24°    decomposes 

C6Cl6(Br6,Ifl)  .......     229°     326° 


Benzene  and  its  homologues  can  give  rise  to  (A)  additive 
compounds  with  bromine  or  chlorine,  or  (B)  substituted  deri- 
vatives. 

A.  Additive  Compounds 

These  are  of  comparatively  little  importance,  and  are  formed 
when  the  hydrocarbon  is  exposed  for  some  time  to  chlorine  or 
bromine  vapour  in  bright  sunlight. 

Benzene  hexachloride,  C6H6C16,  exists  in  two  stereo-isomeric 
modifications;  the  one  melts  at  157°,  and  the  other  sublimes  at 
310°.  When  warmed  with  alkali,  they  yield  trichloro-benzene 
and  HC1.  The  isomerism  is  probably  due  to  the  different 
arrangement  of  the  halogen  atoms  on  either  side  of  the  plane 
of  the  benzene  ring  in  the  two  compounds.  The  hexabromide 
(Matthews,  J.  C.  S.  1901,  79,  43)  melts  at  212°. 

B.  Substituted  Derivatives 

Haloid  substitution  products  in  immense  number  are  derived 
from  the  benzene  hydrocarbons  by  the  exchange  of  hydrogen 
for  halogen.  They  are  either  colourless  mobile  liquids  or 


SUBSTITUTED  HALOGEN  DERIVATIVES  855 

crystalline  solids,  insoluble  in  water  but  readily  soluble  in 
alcohol  and  ether,  distil  unchanged,  and  are  distinguished  by 
their  peculiar  odour  and  also,  in  part,  by  their  irritant  action 
upon  the  mucous  membrane.  They  are  heavier  than  water. 

The  substitution  products  of  benzene  and  its  homologues 
may  be  arranged  in  two  distinct  groups.  In  one  the  halogen 
is  bound  very  firmly,  far  more  so  than  in  methyl  chloride, 
ethyl  iodide,  &c.;  it  cannot  be  exchanged  for  OH  (by  means 
of  AgOH),  or  for  NH2  (by  NH3),  &c.,  but  reacts  with  sodium 
(see  the  Fittig  reaction,  p.  344) ;  A.  332,  38 ;  for  an  exception, 
see  B.  1892,  25,  1499;  1895,  28,  2312;  and  magnesium  (see 
below).  All  the  substituted  derivatives  of  benzene  and  many 
common  derivatives  of  its  homologues  belong  to  this  class. 

In  the  second  group,  of  which  benzyl  chloride  is  a  good 
type,  the  halogen  atoms  enter  into  reaction  as  readily  as  do 
those  of  the  haloid  substitution  products  of  the  methane  series. 

When  the  members  of  the  first  group  are  subjected  to  oxi- 
dation, a  process  which  converts  side  chains  into  carboxylic 
groups,  chloro-derivatives  of  benzoic  and  other  acids  are  ob- 
tained. The  members  of  the  second  group,  when  subjected  to 
similar  treatment,  yield  aromatic  acids  which  are  free  from 
halogen,  e.g.  benzoic  acid,  C6H5»C02H,  phthalic  acid, 
C6H4(C02H)2.  From  this  it  follows  that  the  halogen  is 
present  in  the  first  case  in  the  benzene  nucleus,  and  in  the 
second  in  the  side  chain.  Chloro-toluene  is  C6H4C1»CH3,  and 
benzyl  chloride  C6H5.CH2C1. 

When  the  halogen  atoms  replace  hydrogen  atoms  of  the 
benzene  nucleus,  the  products  are  extremely  stable,  and  the 
halogen  cannot  readily  be  removed  from  the  molecule.  On 
the  other  hand,  when  the  halogen  replaces  hydrogen  atoms  of 
a  side  chain  (methyl  or  ethyl  groups),  the  compound  is  ex- 
tremely reactive,  and  closely  resembles  the  halogen  derivatives 
of  the  fatty  series.  In  this  way  it  is  always  easy  to  arrive 
at  the  constitution  of  a  compound  from  the  behaviour  of  its 
halogen  atoms  and  from  its  products  of  oxidation.  Thus  a 
compound  C7H6C12,  which  yields  monochloro-benzoic  acid  upon 
oxidation,  has  manifestly  the  formula  C6H4C1  •  CH2C1  (chloro- 
benzyl  chloride). 

The  majority  of  aromatic  halogen  derivatives,  independently 
of  the  position  of  the  halogen  in  the  side  chain  or  nucleus, 
react  in  dry  ethereal  solution  (or  in  benzene  in  presence  of  a 
little  dimethyl-aniline)  with  dry  magnesium  powder,  yielding 
organo-magnesium  compounds,  e.g.  C6H5-Mg«Br,  phenyl-mag- 


356  XIX.   HALOGEN  DERIVATIVES 

nesium  bromide,  C6H5  •  CH2  •  Mg  •  Cl,  benzyl-magnesium  chloride, 
&c.  These  compounds  —  Cmgnard's  compounds  —  are  chemically 
extremely  active,  and,  like  the  analogous  aliphatic  compounds 
(p.  120),  can  be  employed  for  the  syntheses  of  saturated  and 
unsaturated  hydrocarbons,  primary,  secondary,  and  tertiary 
alcohols,  thiophenols,  aldehydes,  ketones,  acids,  &c.,  e.g.: 

1.  C6H6.Mg.Br  +  Br.C2H6  =  MgBr2  +  C6H6.C2H6. 

a    C6H5.Mg.Br  +  0  =  C6H6.O.MgBr. 

2-  C6H6.0-MgBr  +  H20  =  C6H6.QH  +  Br-Mg-OH. 

,   C6H6.Mg.Br  +  C02  =  C6H6.CO2.MgBr. 

*  C6H6.CO2MgBr  +  H.OH  =  C6H6-CO2H  +  OH-Mg.Br. 


and  with  water  (C6H6),C  •  OH. 

The  Grignard  compounds  may  also  be  used  for  converting  a 
bromo-derivative  into  the  corresponding  iodo-compound,  e.g.  : 

C6H6Br  —  C6H5-Mg.Br  —  C6H6I  +  MgBrl. 
Mg  I, 

The  boiling-points  of  the  isomeric  halogen  substitution  pro- 
ducts differ  but  little  from  one  another  (cf.  0-,  m-t  ^?-chloro- 
benzene  and  benzyl  chloride). 

The  influence  of  the  introduction  of  F,  Cl,  Br,  or  I  in  place 
of  hydrogen  on  the  boiling-point  of  a  hydrocarbon  is  similar 
to  that  noted  in  the  fatty  series.  Iodine  raises  the  boiling- 
point  to  the  greatest  extent,  and  fluorine  to  the  least. 

The  halogen  derivatives  may  be  nitrated,  sulphonated,  &c., 
in  much  the  same  manner  as  benzene  itself. 

Modes  of  Formation.  —  1.  By  the  action  of  chlorine  or  bromine 
upon  aromatic  hydrocarbons  there  are  formed,  according  to 
the  conditions,  either  additive  or  substitution  products,  the 
latter  class  especially  in  presence  of  iodine  or  some  other 
halogen  carrier.  The  function  of  the  halogen  carrier,  e.g.  I, 
P,  Fe,  &c.,  is  probably  to  form  an  additive  compound  with 
the  halogen,  e.g.  IC13,  PC15,  FeCl3,  then  to  give  up  part  or 
the  whole  of  the  halogen  in  the  nascent  state  to  the  hydro- 
carbon, and  then  to  be  immediately  converted  back  into  the 
above  compounds  again.  (Cf.  p.  56,  also  B.  18.  607.)  Iodine 
only  substitutes  directly  under  the  conditions  detailed  at  p.  57. 
From  benzene  most  of  the  chlorinated  derivatives  up  to 
C6C16  can  be  obtained  in  succession;  the  last-named  compound 
is  formed  with  the  aid  of  MoCl5,  IC13,  &c.,  at  a  somewhat 
high  temperature.  A  hexabromo-benzene  and  a  hexa-iodo-com 


FORMATION  OF  HALOGEN  DERIVATIVE^  357 

pound  also  exist.  In  the  case  of  toluene  and  its  hdniologues 
the  halogen  enters  the  benzene  nucleus  alone  if  the  operation 
is  performed  in  the  cold,  with  the  exclusion  of  direct  sunlight 
or  with  the  addition  of  iodine;  while  if  the  gas  is  led  into  the 
boiling  hydrocarbon,  or  if  the  experiment  is  conducted  in  sun- 
light and  without  addition  of  iodine,  it  goes  almost  exclusively 
into  the  side  chain  (Beilstein;  Schramm;  see  also  B.  13,  1216). 

2.  From  compounds  containing  oxygen  (the  phenols,  aro- 
matic alcohols,  aldehydes,  ketones,  and  acids),  by  the  action 
of  phosphorus  pentachloride  or  bromide: 

C6H5.OH  +  PC15       =  C6H6C1  +  POC13  +  HC1; 
C6H6.CH:O  +  PC15  =  CcH6.CHCl2-f  POC13. 

3.  From  the  primary  amines.     The  amine  is  first  converted 
into  a  diazonium  salt  (p.  385),  and  this  is  then  warmed  with  solu- 
tions of  cuprous  chloride  or  bromide,  when  the  corresponding 
chlorine  or  bromine  compound  is  obtained.     If  the  diazonium 
salt  is  warmed  with  potassium  iodide  solution,  iodo-substitution 
products  are  obtained: 


C6H5.N(C1):N 

C6H6.N(C1):N  +  KI  =  C6H6I  +  N2  +  KC1. 

Gattermann  's  modification  consists  in  transforming  the  amine 
into  the  diazonium  chloride,  bromide,  or  iodide,  and  then  de- 
composing this  with  finely-divided  copper  powder  (Sandmeyw,, 
B.  17,  1633,  2650;  Gattermann,  B.  23,  1218): 

C6H6.NI:N  =  C6H6I  +  N2. 

The  method  is  largely  used  for  the  preparation  of  halogen  de- 
rivatives of  benzene  homologues,  especially  for  iodo-derivatives, 

^-Dibromo-benzene  is  obtained,  together  with  bromo-ben- 
zene,  by  bromination  of  benzene  in  presence  of  a  little  iron. 

The  trichloro-benzene  which  results  by  direct  substitution 
has  the  (asymmetric)  constitution  1:2:4.  It  may  also  be 
formed  by  the  separation  of  3HC1  from  C6H6C16. 

Hexachloro-  and  hexabromo-benzenes  are  produced  by  the 
prolonged  chlorination  or  bromination  of  benzene,  toluene^ 
naphthalene,  &c.,  and  also  from  carbon  tetrachloride  and 
bromide,  as  given  at  p.  343.  They  are  solid  and  can  be 
distilled. 

When  toluene  is  chlorinated  or  brominated,  as  given  on 
p.  356,  the  para-  and  ortho-compounds  are  formed  in  approxi- 
mately equal  quantities.  ra-Chloro-toluene  is  obtained  from 


358  XIX.   HALOGEN  DERIVATIVES 

chloro-^-toluidine,  C6H3C1(NH2)CH3  (from  ^-toluidine  and  Ci), 
according  to  method  3.  Oxidation  by  HN03,  Cr03,  or  KMn04 
converts  them  into  the  haloid-benzoic  acids,  but  chromic  acid 
mixture  must  only  be  used  in  the  case  of  the  p-  and  m-,  and 
not  in  that  of  the  0-compounds,  as  it  completely  disintegrates 
the  latter. 

Benzyl  chloride,  C6H5-CH2C1  (Cannizaro),  is  prepared  by 
chlorinating  boiling  toluene,  and  benzyl  bromide  in  an  analo- 
.gous  manner;  the  latter  can  be  converted  into  benzyl  iodide 
by  potassium  iodide  solution.  The  behaviour  of  these  com- 
pounds shows  them  to  be  the  haloid  esters  of  benzyl  alcohol, 
1C6H5  •  CH2  •  OH,  from  which  they  may  be  obtained  by  the 
action  of  halogen  hydride,  or  of  halogen  derivatives  of  phos- 
phorus, and  into  which  they  are  transformed  by  prolonged 
boiling  with  water,  or  better,  with  a  solution  of  potassium 
carbonate.  When  boiled  with  potassium  acetate,  the  chloride 
yields  benzyl  acetate,  with  potassium  sulph-hydrate  the  mer- 
captan,  and  with  ammonia  the  amine. 

The  compounds  containing  halogen  in  the  side  chain  irritate 
the  mucous  membrane  of  the  nose  and  eyes  exceedingly,  and 
on  oxidation  yield  benzoic  acid.  Benzyl  chloride  is  used  on 
the  large  scale  for  the  preparation  of  oil  of  bitter  almonds  and 
also  of  certain  dyes. 

Benzal  chloride,  Benzylidene  chloride,  C6H5  •  CHC12,  and 
benzo-trichloride,  C6H5«CC13,  are  produced  by  the  further 
chlorination  of  boiling  toluene  and  also  by  the  action  of  PC15 
upon  the  corresponding  oxygen  compounds,  benzaldehyde, 
C6H6»CHO,  benzoic  acid,  C6H5»C02H,  and  benzoyl  chloride, 
C6H5«COC1.  They  are  liquids  resembling  benzyl  chloride, 
and  are  reconverted  into  the  original  oxygen  compounds  by 
superheating  with  water,  and  into  benzoic  acid  by  oxidizing 
agents. 

Chlorobromo-benzenes,  C6H4ClBr,  chlor-iodo-benzenes,  and 
other  mixed  derivatives  also  exist  in  large  number. 

Substitution  compounds  of  unsaturated  hydrocarbons  are 
likewise  known,  e.g.  /3-bromo-styrene,  C6H5  •  CBr :  CH2,  a- 
bromo-styrene,  C6H5  •  CH :  CHBr,  &c. 

Iodine  Derivatives  containing  a  Polyvalent  Iodine  Atom. 
— The  iodine  atom  attached  to  the  nucleus  may  in  many  cases 
unite  with  other  atoms,  and  thus  exercise  a  higher  valency. 
The  compounds  thus  obtained  have  but  few  analogues  in  the 
fatty  series. 

Phenyl-iodide  dichloride,  C6H5«I:C12  (Willgerodt),  is  formed 


NITRO-COMPOUNDS  359 

as  a  yellow  crystalline  compound  when  dry  chlorine  is  led 
into  a  chloroform  solution  of  phenyl  iodide.  The  chlorine  is 
loosely  combined,  and  may  be  removed  on  warming,  or  by  the 
action  of  potassium  iodide.  Alkalis  transform  the  dichloride 
into  iodoso-  benzene,  CgH5-I:0,  a  yellow  amorphous  sub- 
stance which  dissolves  in  acids,  yielding  salts,  e.g.  acetate, 
C6H5.I(C2H302)2,  nitrate,  C6H6.I(0-NO?)2>  &c.  It  decom- 
poses when  heated,  oxidizes  potassium  iodide  solution,  and 
when  kept  or  when  distilled  in  steam  is  converted  into  phenyl 
iodide  and  iodoxy-benzene,  C6H5-I02.  This  latter  is  crystal- 
line, explodes  when  heated,  is  not  basic,  and  resembles  per- 
oxides. It  may  also  be  prepared  by  oxidizing  the  iodoso- 
compound  with  Card's  reagent. 

lodonium  compounds  (Hartmann  and  V.  Meyer,  B.  27,  1592), 
e.g.  diphenyl-iodonium  iodide,  (06H5)2I«I,  and  the  correspond- 
ing hydroxide,  (C6H5)2I  •  OH,  can  be  obtained  when  a  mixture  of 
iodoso-  and  iodoxy-benzene  is  shaken  with  moist  silver  oxide: 

H  =  (C6H6)2I.OH  +  AgIO3. 


The  hydroxide  which  is  only  known  in  solution  has  strongly 
alkaline  properties.  The  salts,  which  crystallize  well,  closely 
resemble  the  thallium  salts.  It  is  highly  probable  that  the 
three  valencies  of  the  polyvalent  iodine  atom  in  these  iodo- 
nium  salts  lie  in  the  same  plane,  as,  according  to  Peters  and 
Kipping  (J.  C.  S.  1902,  1350),  stereo-isomerides  of  the  form 
RR'I  •  X  do  not  appear  to  exist,  and  no  resolution  into  optically 
active  components  can  be  effected. 


XX.  NITRO-SUBSTITUTION  PKODUCTS  OF  THE 
AROMATIC  HYDROCARBONS 

When  benzene  and  its  derivatives  are  treated  with  concen- 
;rated  nitric  acid,  most  of  them  are  easily  dissolved,  with  evo- 
ution  of  heat,  and  transformed  into  mtro-compounds  which 
re  precipitated  on  the  addition  of  water.  According  to  the 
onditions  of  the  experiment  and  the  nature  of  the  compound 
;o  be  nitrated,  one  or  more  nitro-groups  enter  the  molecule 
see,  e.g.,  phenol).  The  nitro-groups  substitute  in  the  nucleus, 
nd  only  very  seldom  in  the  side  chain  (cf.  p.  363). 

Very  often  fuming  nitric  acid  or  a  mixture  of  fuming  nitric 
nd  concentrated  sulphuric  (or  fuming  sulphuric)  acid  is  used. 


360  XX.   AROMATIC  NITRO-COMPOUNDS 

The  advantage  of  the  addition  of  sulphuric  acid  is  to  absorb 
the  water  formed  during  nitration,  and  thus  to  keep  the  nitric 
acid  from  becoming  too  dilute.  The  stronger  the  acid  and 
the  higher  the  temperature,  the  larger  the  number  of  nitro- 
groups  introduced.  The  homologues  of  benzene  are,  as  a  rule, 
nitrated  more  readily  than  benzene  itself. 

SUMMARY 


C«H^NO> 

Nitro-benzene  .  . 

Positions  of 
Substituents. 

M.-p. 

+3° 

B.-p. 
908° 

Sp. 
gr. 
1.204 

CflH4(N02)2.  .. 

o-Dinitro-benzene.... 

1:2 

117° 

319° 

C6H8(N02)8  
CHs-CeH^NO.,... 

m-Dinitro-benzene  ... 
2>-Dinitro-benzene  ...  . 
s-Trinitro-benzene  .  .  . 
os-Trinitro-benzene  . 
o-Nitro-  toluene  
wi-Nitro-toluene  . 

1:3 
1:4 
1:3:5 
1:2:4 
*1:2 
1:3 

90° 
172° 
122° 
57-5° 
-10-5° 
+  16° 

302° 
299° 

t 

218° 
?30° 

1-168 
1-168 

^?-Nitro-toluene  

1:4 

51° 

934° 

f  1-123 

CH8.C6HV(N02)2 
(CH8)2  •  C6H8  •  N02 

2:4-Dinitro-toluene  .  .  . 
2:6-Dinitro-toluene  .  .  . 
4-Nitro-xylene  .  .  . 

.       1:2:4 
.       1:2:6 
.      1:3:4 

70° 
66° 

+2° 

t 
946° 

\  (54°) 
1  -135 

(CH^CJL.NO,.. 

Nitro-mesitvlene.  .  .  , 

.     1:3:5:2 

44° 

255° 

Nitro-compounds  are  also  produced  by  the  action  of  nitrous 
acid  upon  diazonium  compounds  in  the  presence  of  cuprous 
oxide  (Sandmeyer,  B.  20,  1494): 


C6H6NC1:N  +  HN02  =  C6Hfi.N02  +  HC1  +  N2, 

and  also  by  the  oxidation  of  primary  aromatic  amines  : 
C6H5.NH2  —  CCH6.N02 

(Bamberger,  B.  1893,  26,  496).  These  reactions,  however,  are 
mainly  of  theoretical  interest. 

They  cannot,  however,  be  prepared  according  to  mode  of 
formation  1  for  nitro-methane  (p.  94),  i.e.  by  the  action  of 
AgN02  on  C6H5C1,  &c. 

The  nitro-compounds  are,  for  the  most  part,  pale-yellow 
liquids  which  distil  unchanged  and  volatilize  with  water 
vapour;  some  form  colourless  or  pale-yellow  crystals;  some- 
times they  are  also  of  an  intense  yellow  or  red  colour.  Many 

*  The  positions  of  CH3  group,  or  groups,  are  always  given  first. 
t  Most  of  the  polynitro-compounds  are  not  volatile,  but  decompose 
when  heated. 


#ALOir>  NITRO-COMPOUNDS  361 

of  them  explode  when  heated.  They  are  heavier  than  water, 
and  insoluble  in  it;  but  most  of  them  are  readily  soluble  in 
alcohol,  ether,  and  glacial  acetic  acid. 

The  nitro-group  in  most  aromatic  nitro-compounds  is  bound 
very  firmly,  as  in  the  case  of  the  nitre-methanes,  and  is  not 
exchangeable  for  other  groups.  Like  the  latter  compounds 
also,  they  are  readily  reduced  in  acid  solution  to  the  corre- 
sponding amines;  in  alkaline  solution  they  are  converted  into 
azoxy-,  azo-,  and  hydrazo- compounds  (see  these),  and  in 
neutral  solution  into  hydroxylamine  derivatives. 

When  reduced  electrolytically,  nitro -benzene  can  yield 
either  phenyl-hydroxylamine,  C6H5«NH-OH,  which  is  imme- 
diately transformed  into  p-amino- phenol,  OH»C6H4«NH2 
(Gattermann,  B.  1893,  26,  1814;  1894,  27,  1927),  or  it  can 
yield  aniline.  Other  nitro-compounds  can  be  reduced  in  a 
similar  manner.  When  hydrogen  is  passed  into  an  alcoholic 
solution  of  nitro-benzene  containing  colloidal  palladium,  aniline 
is  formed. 

Nitro-benzene,  C6H5(N02)  (Mitscherlich,  1834),  is  formed 
when  a  mixture  of  sulphuric  and  the  calculated  quantity  of 
nitric  acid  is  added  to  benzene.  It  is  a  yellowish  liquid  with 
an  intense  odour  of  oil  of  bitter  almonds,  which  solidifies  in 
the  cold,  and  melts  at  +5°. 

Dinitro-benzenes,  C6H4(N02)2  are  produced  when  benzene 
is  boiled  with  fuming  nitric  acid;  in  this,  as  in  all  analogous 
cases,  the  two  nitro  groups  take  up  the  meta-position  to  one 
another,  very  little  of  the  o-  and  ^-compounds  being  formed, 
and  after  crystallizing  from  alcohol,  pure  m-dinitro-benzene  is 
obtained  in  long  colourless  needles. 

The  0-compound  crystallizes  in  plates  and  the  ^-compound 
in  needles,  both  being  colourless;  they  are  prepared  indirectly 
by  eliminating  NH2  from  the  corresponding  di-nitranilines. 

When  reduced,  they  yield  first  the  three  nitranilines,  and 
then  the  phenylene-diamines  (pp.  374  and  380). 

o-Dinitro-benzene  exchanges  a  nitro-group  for  hydroxyl  when 
boiled  with  caustic  soda,  and  for  an  amino-group  when  acted 
on  by  ammonia,  yielding  o-nitro-phenol,  C6H4(N02)(OH),  and 
0-nitraniline,  C6H4(N02)(NH2),  respectively.  These  reactions 
appear  to  be  characteristic  of  all  compounds  containing  two 
nitro-groups  in  ortho-positions.  The  ?w-compound  is  oxidiz- 
able  by  K3FeC6N6  to  a-  and  /3-dinitro-phenol. 

s-Trinitro-benzene  crystallizes  in  colourless  plates,  melts  at 
122°,  and  forms  additive  compounds  with  aromatic  hydro- 


362  XX.    AROMATIC   NITRO-COMPOUNDS 

carbons,  phenols,  and  especially  with  aromatic  bases,  e.g.  ani- 
line, naphthylamine.  Most  of  these  are  well-defined  crystal- 
line compounds  of  red,  reddish-brown,  or  black  colour,  and  are 
readily  resolved  into  their  components  by  warm  mineral  acids 
(A.  1882,  215,  344;  J.  C.  S.  1901,  522;  1903,  1334;  1906, 
583;  1910,  773). 

Nitro-toluen.es,  CH3»C6H4«N02. — When  toluene  is  nitrated, 
the  p-  and  0-compounds,  with  very  little  wi-compound,  are 
formed.  The  first  is  solid,  crystallizing  in  large  prisms,  and 
the  second  liquid,  the  latter  being  used  as  a  perfume  under 
the  name  of  "  oil  of  mirbane";  both  are  employed  in  the  colour 
industry.  m-Nitro- toluene  can  be  prepared  indirectly  from 
m-nitro-^-toluidine,  C6H3(CH3)(NO2)(NH2),  by  the  elimination 
of  the  ammo-group  (p.  387).  Further  nitration  gives  rise  to: 

Dinitro- toluenes,  CH3  •  C6H3(N02)2,  of  the  constitution 
OH3:N02:N02  =  1:2:4  and  1:2:6,  the  two  nitro-groups 
being  again  in  the  m-position  to  one  another  in  both  cases. 
(Cf.  p.  361.) 

Most  of  these  nitro-compounds  are  of  great  technical  im- 
portance, on  account  of  the  readiness  with  which  they  are 
reduced  to  amines. 

Trinitro-tertiary-butyl-toluene,  C6H(CH3)[C(CH3)3](N02)3, 
is  used  as  "artificial  musk". 

Chloro-  and  Bromo-nitro-benzenes, — When  chloro-  or  bromo- 
benzene  is  nitrated,  ^-chloro-  (or  bromo-)  nitro-benzene  is 
formed,  together  with  smaller  quantities  of  the  o-compounds. 
The  ra-compounds  "must  be  prepared  indirectly  by  replacing 
an  amino-group  in  m-nitraniline  by  halogen.  The  ^-deriva- 
tives have  a  higher  melting-point  than  their  isomers,  and  the 
m-compounds  for  the  most  part  a  higher  one  than  the  0-deri- 
vatives,  this  law  frequently  repeating  itself  in  other  cases  also. 
The  p-derivatives  are  usually  also  less  soluble  in  alcohol.  The 
o-  and  ^-compounds,  but  not  the  w-,  exchange  halogen  for 
hydroxyl  when  boiled  with  potash,  and  for  the  amino-group 
when  heated  with  ammonia. 

In  s-trinitro-chloro-benzene,  C6H2(N02)3C1,  and  in  1-chloro- 
2 : 4-dinitro-benzene  the  chlorine  atoms  have  been  rendered  so 
readily  exchangeable,  that  the  compounds  behave  as  alkyl 
chlorides,  or  even  as  acid  chlorides;  hence  the  name  "picryl 
chloride",  the  chloride  of  picric  acid  (p.  414),  for  the  former 
compound. 

0-,  m-y  and  ^-Nitro-cinnamenes,  C0H4(N02)(C2H3),  can  be 
prepared  by  indirect  methods.  a-Nitro-styrene,  C6H6-CH; 


PHENYL-NITRO-METHANE  363 

CH'N02,  which  is  formed  by  the  action  of  nitrous  acid  on 
cinnamene,  contains  the  nitro-group  in  the  side  chain,  since  it 
can  be  prepared  from  benzoic  aldehyde  and  nitro-methane  by 
means  of  zinc  chloride,  thus: — 

C6H6  •  CHO  +  CH3  •  NO2  =  C6H6 .  CH :  CH .  NO2  +  H2O. 

o-Nitro-phenyl-  acetylene,  N02  •  C6H4  •  C  •  CH,  is  formed 
when  o-nitro-phenyl-propiolic  acid  is  boiled  with  water.  It 
crystallizes  in  colourless  needles. 

Phenyl-nitro-methane,  C6H5  •  CH2«N02,  isomeric  with  the 
nitro-toluenes,  is  the  most  typical  of  the  aromatic  nitro-deriva- 
tives  with  a  nitro-group  in  the  side  chain.  It  is  formed  by  the 
action  of  nitric  acid  (D  1-12)  on  toluene  under  pressure,  and 
also  by  the  action  of  benzyl  halides  on  silver  nitrite  (cf.  Nitro- 
methane).  It  is  a  true  nitro-derivative,  and  not  an  alkyl 
nitrite  (benzyl  nitrite,  C6HB.CH2.O.N:0),  as  it  is  not  readily 
hydrolysed,  and  when  reduced  yields  benzylamine,  C6H5« 
CH2-NH2.  It  exists  in  two  distinct  modifications,  which  are 
readily  transformed  into  each  other.  As  generally  prepared, 
it  is  a  colourless  liquid  with  a  characteristic  odour,  boils  at 
225°-227°,  and  dissolves  to  a  certain  extent  in  water,  yielding 
a  solution  which  does  not  give  a  coloration  with  ferric  chloride. 
The  second  modification,  which  is  a  crystalline  solid  melting 
at  84°,  is  formed  when  the  sodium  derivative  obtained  from 
the  oily  compound  is  decomposed  in  the  cold  by  hydrochloric 
acid.  The  solid  modification  is  relatively  unstable,  and  when 
kept,  gradually  passes  over  into  the  oily  form.  The  solid  is 
probably  a  hydroxy-compound,  since  (a)  its  aqueous  solution 
gives  a  red-brown  coloration  with  ferric  chloride,  (b)  it  reacts 
with  phenyl-carbimide,  (c)  it  reacts  with  PC15,  and  (d)  with 
benzoyl  chloride  it  gives  dibenzhydroxamic  acid, 

C6H6.CO.NH.O.COC6H5  (from 

The  solid  would  thus  be  represented  by  the  formula: 
C6H6.CH:NO-OH    or  perhaps    C6H5.CH-N.OH, 

O 

-an  &09ulr0-fonnula,  the  sodium  salt  by  C6H5»CH:NO'ONa, 
and  the  oil  by  C6H5-CH2-N02.  The  tendency  to  form  iso- 
nitro-compounds  is  also  shown  by  certain  aliphatic  nitre-com- 
pounds. 


364  XX.   AROMATIC  NITRO-COMPOUND8 

The  oily  compound,  although  it  gives  rise  to  a  sodium  salt, 
is,  strictly  speaking,  not  an  acid ;  it  is  what  is  termed  a  pseudo- 
acid,  and  before  it  yields  a  sodium  salt  it  undergoes  intra- 
molecular rearrangement,  yielding  the  true  acid — the  isomtro- 
compound.  When  the  sodium  salt  is  treated  with  a  mineral 
acid,  the  fsonitro-compound,  or  true  acid,  is  first  formed;  but 
as  this  is  unstable,  it  gradually  changes  over  into  the  true 
nitro-  or  pseudo-acid  form.  Numerous  examples  of  pseudo- 
acids,  i.e.  compounds  which  on  formation  of  metallic  salts 
undergo  intramolecular  rearrangement  so  that  the  original 
substance  has  a  structure  different  from  that  of  the  salt,  have 
been  investigated  by  Hantzsch  (B.  1899,  32,  575;  1902,  35,  210, 
226, 1001;  1906,  39, 139, 1073,  &c.),  who  describes  the  following 
as  some  of  the  most  characteristic  criteria  of  pseudo-acids: — 

1.  The  compound  is  a  pseudo-acid  if  it  gradually  neutralizes 
an  alkali.     The  pseudo-acid,  as  such,  does  not  neutralize  the 
base,  but  is  first  transformed  into   the   isomeric   true  acid, 
which  then  neutralizes  the  alkali.     If  the  transformation  is 
slow,  then  the  process  of  neutralization  is  also  slow.    Similarly, 
if  when  a  solution  of  a  salt  of  the  acid  is  decomposed  by  an 
equivalent  quantity  of  a  mineral  acid,  the  electrical  conductivity 
gradually  falls  to  that  required  for  the  metallic  salt  of  the 
mineral  acid,  it  indicates  that  the  acid  is  a  pseudo-acid,  e.g. 
barium  esonitro-methane  +HC1  give  isonitro-methane  +BaCl2, 
and  then  nitro-methane  -f-BaCl2.     Isonitro-methane  is  a  fairly 
strong  acid,  and  hence  is  dissociated  to  an  appreciable  extent; 
as  it  becomes  transformed  into  nitro-methane  (the  pseudo- 
acid)  the  conductivity  will  diminish,  as  nitro-methane  is  an 
extremely  feeble  acid — scarcely  ionized. 

2.  If  the  original  compound  is  extremely  feebly  acidic,  and 
yet  yields  a  sodium  derivative  which  dissolves  in  water  yield- 
ing a  practically  neutral  solution,  then  the  compound  must  be 
a  pseudo-acid.     It  is  a  well-known  fact  that  only  sodium  salts 
derived  from  comparatively  strong  acids,  e.g.  NaCl,  Na2S04, 
Nal,  &c.,  dissolve  in  water  to  neutral  solutions,  i.e.  are  not 
hydrolysed  by  water.     The  sodium  salts  derived  from  feeble 
acids  are  always  appreciably  hydrolysed,  e.g.  Na2C08,  CH3« 
COONa,  &c.     Hence  if  the  sodium  salt  is  not  hydrolysed  to 
an  appreciable  extent,  the  salt  must  be  derived  from  a  strong 
acid  (the  true  acid),  and  the  non-  or  feebly  acidic  compound 
must  be  the  pseudo-acid. 

3.  If  the  compound  in  question  will  not  yield  a  salt  with 
ammonia  in  an  anhydrous  solvent,  e.g.  dry  benzene,  but  will 


NITROSO-DERIVATIVES  365 

do  so  in  the  presence  of  water,  e.g.  in  moist  ether,  then  the 
substance  is  a  pseudo-acid.  The  formation  of  a  salt  in  dry 
ether  does  not  necessarily  indicate  that  the  substance  is  a 
true  acid. 

4.  If  the  compound  dissolves  in  water  or  in  other  dissociating 
(ionizing)  media  to  a  colourless  solution,  but  yields  a  coloured 
solid  salt  or  coloured  ions  when  dissolved  in  alkalis,  it  is  a 
pseudo-acid. 

5.  An  abnormally  high  temperature  coefficient  for  the  elec- 
trical conductivity  and  an  increase  in  the  coefficient  with  rise 
of  temperature  are  further  indications  of  pseudo-acids. 

Nitro- methane,  bromo-nitro-methane,  dibromo-nitro-meth- 
ane,  nitro-ethane,  phenyl-nitro-methane,  phenyl-bromo-nitro- 
methane,  in  addition  to  numerous  other  organic  compounds, 
e.g.  cyanuric  acid,  react  as  pseudo-acids. 

NITROSO-DERIVATIVES  OF  THE  HYDROCARBONS 

Nitroso-benzene,  C6H5.N:0,  an  aromatic  compound  which 
contains  the  nitroso-group,  »N:0,  in  place  of  a  benzene  hy- 
drogen atom,  is  produced  by  the  action  of  nitrosyl  chloride, 
NO'Cl,  upon  mercury  diphenyl  dissolved  in  benzene;  it  is 
also  obtained  by  the  oxidation  of  diazo-benzene  with  alkaline 
permanganate,  and  most  readily  by  the  oxidation  of  phenyl- 
hydroxylamine  with  chromic  acid  or  ferric  chloride.  It  forms 
colourless  plates,  melts  at  68°,  yields  green  solutions,  and  pos- 
sesses a  powerful  odour  similar  to  that  of  cyanic  acid.  When 
reduced  it  yields  aniline,  and  when  oxidized  nitro-benzene. 
It  readily  condenses  with  different  compounds,  e.g.  with  ani- 
line in  the  presence  of  acetic  acid  to  azo-benzene: 

CCH5.N:0  +  H2N.C6H6  =  H2O  +  C6H5.N:N.C6Hfi) 

and  with  phenyl-hydroxylamine  to  azoxy-benzene. 

Nitroso-derivatives  of  tertiary  amines  are  obtained  directly 
by  the  action  of  nitrous  acid  upon  the  latter.  (See  Nitroso- 
dimethyl-aniline,  NQ.C6H4.N(CH3)2,  p.  378.) 


366  XXI.    ARYLAMINKS 

XXL  AMINO-DERIVATIVES  OR  ARYLAMINES* 

(See  Table,  p.  367.) 

Aniline,  the  simplest  of  the  aromatic  bases,  may  be  regarded 
(1)  as  benzene  in  which  a  hydrogen  atom  is  replaced  by  the 
amino-group  ("amino-benzene"),  or  (2)  as  ammonia  in  which 
a  hydrogen  atom  is  replaced  by  phenyl,  C6H5»,  ("phenyl- 
amine").  According  to  the  former  view,  ammo-compounds 
can  be  derived  from  all  the  benzene  hydrocarbons,  and  not 
only  monamines  (containing  NH2),  but  also  diamines  (2NH2), 
triamines,  &c.;  according  to  the  latter,  the  phenyl  group 
may  enter  anew  with  the  formation  of  secondary  or  tertiary 
amines.  Secondary  and  tertiary  amines,  and  even  quaternary 
ammonium  compounds,  may  also  result  from  the  entrance  of 
alky  1- radicals  into  the  above  monamines,  diamines,  &c. 
Amines  are  also  known  in  which  the  NH2  group  is  attached 
to  a  carbon  atom  of  a  side  chain,  e.g.  C6H5»CH2«NH2.  These 
compounds  differ  in  many  respects  from  aniline  and  its  homo- 
logues. 

An  extraordinarily  large  number  of  aromatic  bases  are  thus 
theoretically  possible,  and  also  actually  known.  In  certain 
respects  they  closely  resemble  the  aliphatic  amines,  e.g.  they 
form  salts  with  acids,  e.g.  (XH5NH2,  HC1,  and  complex  salts, 
e.g.  platinichlorides  and  auricnlorides,  2C6H5NH2,  H2PtCl6  and 
C6H6NH2,  HAu014;  they  possess  a  basic  odour,  give  rise  to 
white  clouds  with  volatile  acids,  and  distil  for  the  most  part 
unchanged,  &c.  As  a  rule,  however,  they  are  weaker  bases 
than  the  aliphatic  amines,  since  the  phenyl  group,  C6H5,  pos- 
sesses a  negative  character,  and  not — like  the  alphyl  radicals — 
a  positive;  thus  the  salts  of  diphenylamine  are  decomposed 
even  by  water,  and  triphenylamine  no  longer  possesses  basic 
properties,  while  dimethyl-aniline  has  a  strongly-marked  basic 
character. 

*  To  distinguish  between  monovalent  alcoholic  or  hydrocarbon  radicals 
of  the  fatty  and  aromatic  series  the  following  system  has  been  suggested : — 
The  term  alkyl  group  comprises  all  such  monovalent  radicals  whether  of 
the  aliphatic  series,  e.g.  CH8,  C2H5,  or  of  the  aromatic,  e.g.  C«Hfc  CHs.C6Ht, 
C6H5'CHo,  &c.  The  purely  aliphatic  alkyl  radicals  are  termed  alphyl 
groups,  and  the  aromatic,  aryl  ( Vorlander,  J.  pr.  [2],  69,  247).  Thus  anil/ ue 
is  often  spoken  of  as  a  type  of  the  arylamines. 


PRIMARY  MONAMINES 


367 


The  diamines  have  a  more  strongly  basic  character  than  the 
monamines,  and  are  more  readily  soluble  in  water. 

ANILINE  AND  ITS  HOMOLOGUES 


Formula. 
CflH,.NH9.. 

Name.               1 

Positions  of 
iubstituents 
NH2  in  1. 

M.-p.     B.-p. 

—8°    183° 

M.-p.  of 
Acetyl 
Derivative. 

115° 

CJELMe-NH,.. 

o-Toluidine  

1-2 

liq      199° 

110° 

1:3 

liq.     199° 

65'5° 

#-Toluidine        ... 

1:4 

42  '8°   198° 

153° 

C6H3Me2-NH2.. 

ac?/.-0-xylidene  .... 
wnsywi.-o-xylidene 
ac^'.-m-xylidene.  .  . 
»-xylidene  

1:2:3 
1:3:4 
1:2:6 
1:2:5 

liq.     223° 
49°    226° 
liq.     215° 
15'5°  215° 

134° 
99° 
176° 
139° 

C6H2Me3«NH2  . 

Mesidine  

1-2-4-6 

liq      233° 

216° 

C6H6-NHMe... 
C6H6.NMe2  

Pseudo-cumidine  . 

Methyl-aniline.... 
Dimethyl-aniline  . 

1:2:4:5 

68°    234° 

...     192° 
...     192° 
...     204° 

164° 
101-102° 

54'50 

(lld-NEt, 

Diethyl-aniline  .  . 

213° 

183° 

60° 

A.  Primary  Monamines 

Isomers. — The  isomerism  of  the  aromatic  is  in  part  analogous 
to  that  of  the  fatty  amines  (p.  107),  e.g.  dimethyl-aniline  is 
isomeric  with  the  methyl-toluidines  and  the  xylidines.  Cases 
of  isomerism  are  also  caused  by  the  amino-group  being  present 
in  the  benzene  nucleus  in  the  one  case,  and  in  the  side  chain 
in  the  other.  Finally,  position  isomerides  are  frequently  met 
with,  e.g.  0-,  m-,  and  ^-toluidines,  CH3  •  C6H4  •  NH2. 

Constitution. — As  already  seen  at  pp.  108  et  seq.,  amines  are 
very  easy  to  characterize  as  primary,  secondary,  &c.  In 
addition,  their  modes  of  formation,  and  also  their  behaviour, 
show  whether  the  amino-group  of  a  primary  amine  is  present 
in  the  benzene  nucleus  or  in  the  side  chain. 

Modes  of  Formation. — 1.  The  most  important  mode  of  pre- 
paration of  the  primary  arylamines,  whether  mono-  or  di-,  &c., 
is  the  reduction  of  the  corresponding  nitro-compounds : 

C6H6.N02 

Nitro-benzene 

C6H4(N02)2H 
Diuitro-benzene 


Aniline. 


4H20  +  C6H4(NH2)2 

Phenylene-diamine. 


368  XXI.   ARYLAMINES 

The  usual  method  of  introducing  an  ammo-group  into  a 
benzene  hydrocarbon  is  to  first  nitrate  and  then  reduce.  An 
interesting  direct  method  for  the  introduction  of  the  NH 
group  is  by  the  action  of  ferric  or  aluminic  chloride  on  a 
mixture  of  the  hydrocarbon  and  hydroxylamine  hydrochloride 
(B.  1901,  34,  1778): 

NH.OH  = 


The  reduction  of  nitro-  to  amino-compounds  takes  place 
most  readily  in  acid  solution,  e.g.  by  the  gradual  addition  of 
the  former  to  a  warm  mixture  of  tin  or  stannous  chloride 
and  hydrochloric  acid.  On  a  manufacturing  scale,  iron  and  a 
limited  amount  of  hydrochloric  acid  are  used  (Be~champ\  also 
frequently  zinc  dust  and  hydrochloric  or  acetic  acid.  Am- 
monium sulphide  (Zinin),  ferrous  sulphate,  and  baryta  water, 
&c.,  also  effect  the  reduction.  (See  Aniline  and  chapter  on 
Eeduction.) 

Aniline  and  its  homologues  may  also  be  obtained  by  the 
electrolytic  reduction  of  nitro-compounds. 

Ammonium  sulphide  acts  more  mildly  than  tin  and  hydro- 
chloric acid,  and  is  therefore  of  special  value  for  the  partial 
reduction  of  dinitro-compounds  (see  Nitraniline).  An  alcoholic 
solution  of  stannous  chloride  containing  hydrochloric  acid  may 
also  be  used  for  this  purpose  (B.  19,  2161). 

Amines  are  also  formed  when  nitroso-compounds  and  aryl- 
hydroxylamines  are  reduced. 

2.  By  heating  phenols  with  the  compound  of  zinc  chloride 
and  ammonia,  or  of  calcium  chloride  and  ammonia,  to  300° 
(Merz),  secondary  amines  being  formed  at  the  same  time: 

C6H6.iOH"+H;NH2  = 


This  reaction  proceeds  more  easily  in  the  presence  of  nega- 
tive groups,  e.g.  with  the  mtro-phenols  (B.  19,  1749). 

3.  By  distilling  amino-acids  with  lime,  sometimes  by  merely 
heating  them  alone  : 

NH2.C6H4.C02H  =  C6H6.NH2-hC02. 

4.  When    the    hydrochlorides    of    secondary   and    tertiary 
amines  of  the  type  of  mono-  and  di-methyl-aniline  are  heated 
in  sealed  tubes,  the  methyl  groups  wander  from  the  nitrogen 
atom  to  a  carbon  atom  of  the  benzene  nucleus,  e.g.  methyl- 
aniline  hydrochloride  at  335°  yields  toluidine  hydrochloride: 

CflH6.NHCH3,HCl  ^  CH3.CCH4.NH2,HCL 


PROPERTIES   OF  PRIMARY  ARYLAMINES  369 

The  methyl  groups  invariably  take  up  the  o-  or  p-,  and  not 
the  m-  position,  with  respect  to  the  amino-group.  Q 

Similarly,  the  final  product  obtained  by  heating  phenyl- 
trimethylammonium  iodide,  C6H5'NMe3I,  is  mesidine  hy- 
driodide,  CflH2Me8  •  NH2  [NH2 :  Me3  =  1 : 2 : 4 :  6*J.  ftiphenyl- 
amine  hydrochloride  does  not  behave  in  a  similar  manner. 

This  reaction,  often  known  as  the  Hofmann  reaction,  is  of 
considerable  service  in  obtaining  the  higher  homologues  of 
aniline  from  aniline,  toluidine,  &c.  Aniline  is  readily  con- 
verted into  dimethyl-aniline,  and  when  the  hydrochloride  of 
this  is  heated  to  about  300°  the  methyl  groups  wander  from 
the  side  chain  into  the  nucleus: 

C6H6.NMe2  —  CGH3Me2.NH2. 

5.  Primary  amines  can  be  obtained  from  acid  amides  by 
Hofmann' s  reaction  (cf.  p.  183),  viz.  treatment  with  bromine 
and  alkali,  or  from  acid  azides,  K-CO'N3.     When  boiled  with 
alcohol  the  azide  yields  nitrogen  and,  by  molecular  rearrange- 
ment, a  urethane,  R»NH'CO»OEt,  and  this  on  hydrolysis 
gives  a  primary  amine,  RNH2. 

6.  The  aromatic  amines  cannot,  as  a  rule,  be  obtained  by 
heating  chloro-benzene,  &c.,  with  ammonia  unless  there  is  a 
nitro-group  in  the  ortho-  (or  para-)  position  with  respect  to 
the    halogen.      Benzylamine,    however,    and   all   analogously 
constituted  bases,  which  contain  the  NH2  group  in  the  side 
chain,  can  be  obtained  by  the  methods  employed  for  the  pre- 
paration of  aliphatic  amines.     Thus  benzylamine  is  formed  by 
the  action  of  ammonia,  or  better,  of  acetamide  upon  benzyl 
chloride  (the  latter  method  gives  acetyl-benzylamine,  which 
can  be  readily  hydrolysed). 

Properties. — The  primary  monamines  are  either  liquid  or 
solid  crystalline  bases.  They  are  colourless  when  pure,  but 
readily  become  brown  when  exposed  to  the  air,  largely 
owing  to  the  presence  of  small  amounts  of  impurities,  and 
possess  a  weakly  basic  though  not  disagreeable  odour.  Ani- 
line is  somewhat  soluble  in  water  (1:31),  its  homologues 
less  so. 

Behaviour. — 1.  With  acids  most  of  them  form  crystalline 
salts,  the  majority  of  which  are  readily  soluble  in  water. 
They  do  not,  however,  unite  with  very  weak  acids,  such  as 

*  The  numbers  1:2:4:6  indicate  the  relative  positions  of  the  amino-  and 
three  methyl -radicals  in  the  benzene  ring. 

(B480)  ?A 


370  XXI.    ARYLAMINES 

carbonic,  and  they  are  therefore  separated  from  their  salts  in 
the  free  state  by  sodium  carbonate,  and  in  some  cases  even  by 
sodium  acetate  (when  no  acetates  exist).  They  yield  com- 
plex salts,  such  as  platinichlorides,  (C6H5NH2)2,  H2PtCl6,  ami- 
chlorides,  C6H5NH2,  HAuCl4,  ami  similar  compounds  with  stan- 
nous,  stannic,  and  zinc  chlorides.  The  platinum  double  salts 
are  often  sparingly  soluble,  and  therefore  suited  for  the  isolation 
of  the  bases. 

All  salts  of  the  bases  are  readily  decomposed  by  strong 
alkalis,  and  the  free  bases  are  regenerated.  Even  in  aqueous 
solution  the  salts  are  largely  split  up  into  free  acid  and  free 
base;  the  result  is  that  the  strength  of  a  solution  of  aniline 
hydrochloride  may  be  determined  by  titrating  the  hydrochloric 
acid  present  by  standard  alkali  hydroxide,  using  phenol- 
phthalein  as  indicator.  This  is  not  due  to  the  fact  that  the 
salt  is  completely  hydrolysed  in  aqueous  solution;  in  reality 
there  is  a  state  of  equilibrium  represented  by  the  equation: 
C6H6.NH3C1  ^±  C6H6NH2  +  HC1, 

and  as  the  HC1  is  neutralized  by  the  addition  of  alkali,  more 
of  the  aniline  salt  is  decomposed  in  order  to  restore  the  equi- 
librium. This  continues  until  the  whole  of  the  salt  is  decom- 
posed, and  the  HC1  neutralized  by  the  alkali. 

The  amines  also  form  additive  compounds  with  numerous 
metallic  salts,  e.g.  2C6H7N  +  ZnCl2,  2C6H7N  +  HgCl2,  &c. 

2.  When  aniline  is  heated  with  potassium  or  sodium,  the  hy- 
drogen is  replaced  by  metal  with  formation  of  the  compounds 
CgH5NHK  and  C6H5NK2.    These  yield  di-  and  tri-phenylamine 
with  bromobenzene,  and  decompose  immediately  with  water. 

3.  The  primary  arylamines  react  with  methyl  iodide,  benzyl 
chloride,  &c.,  yielding  secondary,  tertiary,  and  even  quaternary 
compounds  : 

=  C6H5.NH(CH3),HI; 


C6H5.NH(CH3)  +  CH3I  =  QgHs-NC 
C6H6.N(CH3)2  +  CH3I     =  C6H5.N(CH3)3I. 

The  secondary  and  tertiary  bases  can  be  liberated  from  their 
hydriodides  by  soda,  but  moist  oxide  of  silver  must  be  used  in 
the  case  of  the  ammonium  bases  (see  p.  109). 

4.  Just  as  the  ammonium  salts  of  acids  can  eliminate  water, 
yielding  amides,  so  the  aniline  salts  can  yield  anilides,  e.g. 
aniline  acetate  gives  acetanilide: 

CH3.CO-ONH3C6H6  =  CH3.CO-NHC6H6-fHaO. 


ANILIDES.      ISONITRILES  371 

These  anilides  may  be  looked  upon  either  as  acetylated 
amines  or  as  phenylated  amides,  the  formula  CH3»CO- 
NH»C6H5  corresponding  with  the  latter  view.  They  are  in 
every  respect  analogous  in  their  chemical  behaviour  to  the 
ordinary  amides,  especially  to  the  alkylated  amides  (p.  182), 
being  hydrolysed  to  the  acid  and  aniline  by  alkalis,  and  being 
formed  by  analogous  methods,  e.g.  by  heating  the  acid,  or 
better,  its  anhydride  or  chloride,  with  the  amine  in  question, 
thus  :  — 

CH3  •  C6H4  •  NH2  +  CH3  •  COC1  =  CH3  •  C6H4  .  NH  •  CO  •  CH3  +  HC1. 

Toluidiue  Acet-toluidide 

5.  Aliphatic  aldehydes  react  with  the  primary  bases,  with 
elimination  of  water,  thus:  — 

CH3.CHO-f  2C6H6.NH2  =  CH3.CH(NH.C6H5)2-f  H2O. 

Ethylidene-diphenyl-diamine 

Aromatic  aldehydes,  however,  react  as  follows  :  — 
C6H5  •  CHO  +  NH2  •  C6H6  =  C6H6  .  CH  :  N  •  C6H6  +  H20. 

In  this  case  an  additive  compound  appears  to  be  first  formed, 
C6H5.CH(OH).NH-C6H5,  and  this  loses  water,  yielding  ben- 
zylidene  aniline,  C6H5  •  CH  :  N  •  C6H5. 

Condensation  products  of  this  latter  kind  (Schiff's  bases) 
can  also  be  obtained  with  the  fatty  aldehydes,  but  they  poly- 
merize readily  (v.  Miller,  Plochl,  B.  25,  2020). 

6.  When  warmed  with  chloroform  and  alcoholic  potash,  the 
primary  bases,  like  those  of  the  fatty  series,  yield  isonitriles 
of  stupefying  odour.      When  they  are  warmed  with  carbon 
disulphide,  thio-ureas  are  formed,  and  from  the  latter  isothio- 
cyanates  (mustard  oils)  by  treatment  with  phosphoric  acid  (cf. 
pp.  276  and  296). 

7.  Bromine  and  chlorine,  especially  in  the  form  of  sodium 
hypochlorite  or  hypobromite,  react  with  amines,  forming  sub- 
stituted derivatives  of  the  type  C6H5-NHBr,  in  which  the 
halogen  is  attached  to  nitrogen.     These  compounds  are  ex- 
tremely unstable,  can  only  be  kept  at  low  temperatures,  and 
the  halogen  atom  readily  passes  from  the  side  chain  into  the 
benzene  nucleus: 

CflH6.NHBr  — 


usually  into  the  para-position  (Chattaway  and  Orton,  J.  C.  S. 
1899,  1046;  1900,  134,  152,  789,  797). 


372  XXI.    AR  FAMINES 

8.  Nitrous  acid  converts  the  primary  aromatic  amines  in 
acid  solution  into  diazonium  salts  (p.  385),  and  in  the  absence 
of  acids  into  diazo-amino-compounds  (p.  392). 

9.  The  oxidation  products  of  the  primary  bases  are  very 
various,  azo-benzene,  nitro-benzene,  ^-amino-phenol,  phenols, 
quinones,  azo-compounds,  aniline  black,  &c.,  resulting  accord- 
ing to  the  conditions;  a  mixture  of  aniline  and  toluidine  yields 
magenta  (fuchsine)  (see  Triphenylmethane  dyes). 

10.  The  bases  which  contain  the  amino-group  in  the  side 
chain   possess,   in   contradistinction   to   the   purely   aromatic 
amines,  the  character  of  the  amines  of  the  fatty  series,  and 
cannot,  therefore,  be  diazotized. 

Aniline,  ammo-benzene,  Phenylamine,  C6H5«NH2,  was  first 
obtained  in  1826  by  Unverdorben  from  the  dry  distillation  of 
indigo,  and  termed  by  him  "crystalline";  then  Eunge  found 
it  in  coal-tar  in  1834,  and  called  it  "cyanol".  In  1841 
Fritsche  prepared  it  by  distilling  indigo  with  potash,  and  gave 
it  the  name  of  aniline;  while  in  1842  Zinin  obtained  it  by  the 
reduction  of  nitro-benzene,  and  called  it  "  benzidam  ".  It  was 
accurately  investigated  by  A.  W.  Hofmann  in  1843,  and  he 
was  able  to  show  that  all  the  above  products  are  identical. 

It  is  present  in  small  quantities  in  coal-tar  and  also  in  bone- 
oil. 

Preparation.  —  Since  1864  aniline  has  been  prepared  on  a 
manufacturing  scale  by  reducing  nitro-benzene  with  iron 
filings  and  a  regulated  quantity  of  hydrochloric  acid,  and 
distilling  with  steam  after  the  addition  of  lime.  The  amount 
of  hydrochloric  acid  actually  employed  is  only  about  j^th  of 
that  required  by  the  equation: 

=  C6H6-NH2  +  2H20  +  3FeCl2. 


This  is  probably  due  to  the  fact  that  water  and  metallic  iron, 
in  the  presence  of  ferrous  chloride,  can  act  as  reducing  agents. 
It  is  a  colourless,  oily,  strongly  refracting  liquid  of  peculiar 
odour,  which  quickly  turns  yellow  or  brown  in  the  air,  and  is 
finally  converted  into  a  resin.  It  dissolves  in  31  parts  of 
water,  has  no  action  upon  litmus,  and  is  a  weaker  base  than 
ammonia,  although  it  can  displace  the  latter  at  higher  tem- 
peratures. It  is  poisonous,  burns  with  a  smoky  flame,  and  is 
a  good  solvent  for  many  compounds  which  are  otherwise  not 
readily  dissolved,  e.g.  indigo  and  sulphur.  Aqueous  solutions 
of  the  salts  have  a  distinct  acid  reaction. 

The  behaviour  of  aniline  has   been  investigated  with   the 


ANILINE  373 

utmost  care.  Oxidation  in  alkaline  solution  leads  to  azo- 
benzene,  while  arsenic  acid  produces  chiefly  violaniline,  a 
violet  colouring-matter.  A  solution  of  free  aniline  is  tem- 
porarily coloured  violet  by  one  of  bleaching- powder,  this 
reaction  being  an  extremely  delicate  one.  A  solution  in  con- 
centrated H2S04  is  first  coloured  red  and  then  blue  by  a  small 
grain  of  potassium  dichromate.  A  solution  of  K2O207  pro- 
duces in  an  acid  solution  of  aniline  sulphate  a  dark-green  and 
then  a  black  precipitate  of  aniline  black  (Willstdtter,  B.  1907, 
40,  2665;  1910,  43,  2976;  Green,  J.  C.  S.  1910,  2388;  B.  1911, 
44,  2570),  and  ultimately  quinone,  C6H402.  A  mixture  of 
aniline  and  toluidine  may  be  oxidized  to  magenta,  mauveine, 
&c.,  and  a  mixture  of  aniline  and  j9-diamines  to  safranines  (see 
these).  When  reduced,  aniline  yields  amino-hexamethylene, 
boiling  at  134°. 

Salts. — Aniline  hydrochloride,  C6H5*NH2,  HC1,  forms  large 
colourless  plates  which  become  greenish-grey  in  the  air  and 
distil  unchanged,  and  aniline  sulphate,  (C6H7N)2,  H2S04,  beau- 
tiful white  plates,  sparingly  soluble  in  water.  The  platini- 
chloride,  (C6H7N)2,  H2PtCl6,  crystallizes  in  yellow  plates,  which 
are  sparingly  soluble. 

Substitution  Products — Halogen  'Derivatives. — Aniline  is  much 
more  readily  substituted  by  halogens  than  benzene,  chlorine 
or  bromine  causing  substitution  of  as  many  as  three  atoms 
of  hydrogen,  yielding  s?/w-trichlor-  or  -tribrom-aniline,  while 
iodine  produces  mono-iodoaniline.  In  the  chlorination  of  ani- 
line it  is  necessary  to  use  a  solvent  free  from  water  (e.g. 
chloroform  or  glacial  acetic  acid),  otherwise  oxidation  and  not 
substitution  occurs.  In  bromination  the  simplest  method  is  to 
aspirate  air  saturated  with  bromine  vapour  through  an  acid  solu- 
tion of  aniline.  In  all  these  reactions  the  halogen  probably 
first  substitutes  H  of  the  NH2  group  (see  p.  371).  In  the 
preparation  of  monochlor-aniline,  the  aniline  must  be  "pro- 
tected" by  using  it  in  the  form  of  its  acetyl  derivative, 
acetanilide.  When  this  is  suspended  in  water,  it  is  mostly 
transformed  by  chlorine  into  p  -  chlor  -  acetanilide,  which 
readily  yields  p-chlor-aniline  on  hydrolysis ;  the  latter  forms 
colourless  crystals,  m.-pt.  71°,  b.-pt.  231°.  The  o-  and  m-com- 
pounds,  which  are  both  liquid,  are  prepared  indirectly,  e.g.  by 
the  reduction  of  o-  or  m-chloro-nitro-benzene. 

The  basic  character  is  weakened  in  the  mono-chlor-anilines 
by  the  entrance  of  the  halogen,  this  being  the  case  particularly 
in  the  0-compounds.  It  is  still  more  striking  in  s-tri  chlor- 


374  XXI.   ARYLAMINJCS 

aniline,  C6H2C13(NH2)  (crystals,  volatile  without  decomposi- 
tion), which  no  longer  combines  with  acids  in  presence  of 
water,  o-  and  ^-Chlor-anilines  are  only  capable  of  taking  up 
two  more  atoms  of  chlorine  with  the  formation  of  trichlor- 
aniline:  [NH2 : Cl : Cl : Cl  =  1.2.4.6];  ra-chlor-aniline,  on  the 
other  hand,  can  be  further  chlorinated  to  tetra-  and  penta- 
chlor-aniline. 

The  bromo-derivatives  of  aniline  closely  resemble  the  chlor- 
anilines,  and  may  be  prepared  by  similar  methods.  The  best- 
known  compound  is  s-tribrom-aniline,  which  is  formed  by  the 
action  of  bromine  water  on  a  solution  of  aniline  hydrochloride. 
It  crystallizes  from  alcohol  in  needles,  and  melts  at  119°. 

As  an  example  of  the  methods  sometimes  employed  for  the 
preparation  of  halogen  derivatives  may  be  cited  the  prepara- 
tion of  2 : 6-dibrom-aniline  from  sulphanilic  acid,  1-amino-ben- 
zene-4-sulphonic  acid.  When  carefully  brominated,  this  yields 
the  2 : 6-dibromo-derivative ;  and  when  this  is  superheated  with 
steam  at  170°  the  sulphonic  acid  group  is  removed,  and  2:6- 
dibrom-aniline,  melting  at  84°,  is  formed. 

Nitranilines. — Aniline  is  likewise  attacked  far  more  vio- 
lently than  benzene  by  concentrated  nitric  acid,  and  therefore 
when  it  is  wished  to  prepare  the  mono-nitro-compounds,  the 
aniline  must  again  be  "  protected  ",  either  by  using  its  acetyl 
compound,  or  by  nitrating  in  presence  of  excess  of  concen- 
trated sulphuric  acid.  In  the  latter  case  all  three  nitranilines 
result,  the  m-compound  preponderating.  When  acetanilide  is 
nitrated,  p-nitr acetanilide,  N02.C6H4-NH«CO.CH3,  and  a 
little  of  the  o-compound,  are  formed,  and  both  are  readily 
hydrolysed  by  potash  or  hydrochloric  acid. 

The  nitranilines  are  further  obtained  by  the  partial  reduc- 
tion of  the  corresponding  dinitro-benzenes,  e.g.  by  means  of 
ammonium  sulphide;  this  is  the  method  usually  employed  for 
the  preparation  of  m-nitraniline.  (For  mechanism  of  the  re- 
action, see  Cohen  and  M'Candlish,  J.  C.  S.  1905,  1257.) 

The  o-  and  ^-compounds  are  also  formed  when  o-  and  p- 
C6H4C1.N02,  C6H4Br.N02,  OH.C6H4.N02,  or  OEt.C6H4.NO? 
are  heated  with  ammonia  at  180°,  and  conversely  the  o-  and 
p-nitranilines  are  converted  into  nitro-phenols  when  boiled 
with  alkalis,  the  former  more  easily  than  the  latter,  thus: — - 

CflH4(N02)(NH2) -f  H-OH  =  C6H4(N02)OH  +  NH3. 

These  are  all  further  examples  of  the  remarkable  influence  of 
nitro- groups  on  other  substituents,  e.g.  Cl,  Br,  OH, 


TOLUIDINE!  375 

&c.,  in  the  o-  and  p-,  but  not  in  the  m-position.  (Cf.  Picryl 
Chloride  and  Picramide.) 

The  three  ni tramlines  crystallize  in  yellow  needles  or 
prisms,  and  are  readily  soluble  in  alcohol,  but  only  very 
slightly  in  water.  They  melt  respectively  at  71°,  114°,  147°, 
and  their  acetyl  derivatives  at  92°,  142°,  and  207°.  The  o- 
and  m-compounds  are  volatile  with  steam,  but  not  ^-nitraniline. 
When  reduced,  they  yield  phenylene-diamines. 

Di-  and  trinitranilines, 

C6H3(N02)2(NH2)    and    *-C6H2(NO2)3(NH2), 

are  likewise  known;  the  latter,  which  is  termed  picramide, 
and  which  crystallizes  in  yellow  needles,  m.-pt.  188°,  comports 
itself  as  the  amide  of  picric  acid,  since  it  is  readily  transformed 
into  the  latter  compound  on  hydrolysis. 

(For  alkyl  derivatives,  see  under  Secondary  and  Tertiary 
Monamines.) 

Homologues  of  Aniline. — Of  the  three  toluidines,  CH3« 
C6H4  •  NH2,  the  o-  and  ^-compounds  are  obtained  by  the 
reduction  of  the  corresponding  nitro-compounds.  The  o-  is 
liquid  and  the  p-  solid. 

m-Toluidine,  which  is  liquid,  may  be  prepared  from  wi-nitro- 
toluene  or  ra-nitro-benzaldehyde  (cf.  B.  15,  2009). 

The  boiling-points  of  the  three  isomeric  toluidines  are  almost 
identical,  but  the  melting-points  of  their  acetyl  compounds 
differ  widely  (see  table,  p.  367) ;  these  are,  therefore,  of  value 
for  the  characterization  ot  the  toluidines.  o-Toluidine  is 
coloured  violet  by  a  solution  of  bleaching-powder,  and  blue  by 
sulphuric  and  nitrous  acids  and  also  by  ferric  chloride,  but  not 
£>-toluidine.  For  their  conversion  into  fuchsine,  see  Triphenyl- 
methane  dyes.  If  during  oxidation  the  amino-group  be  pro- 
tected by  the  introduction  of  acetyl,  the  methyl  radical  can 
be  oxidized  to  carboxyl  and  an  acetyl  derivative  of  amino- 
benzoic  acid  obtained.  When  oxidized  with  KMnO4,  the 
amino-compounds  are  transformed  into  azo-compounds. 

(For  higher  homologues,  see  table,  p.  367.) 

B.  Secondary  Monamines 

We  have  purely  aromatic  secondary  amines,  such  as  di- 
phenylamine,  (C6H5)2NH,  and  mixed  secondary  bases,  which 
contain  both  an  alphyl  and  an  aryl  group,  e.g.  methylaniline. 
CttH6.NH.CH8. 


376  XXI.   ARYLAMINES 

Modes  of  Formation. — 1.  Mixed  secondary  amines  are  formed 
when  the  primary  amines  are  heated  with  alphyl  iodides  (Hof- 
mann)  (see  p.  105). 

This  reaction  does  not  usually  stop  short  with  the  intro- 
duction of  one  alphyl  radical,  but  extends  further  with  the 
formation  of  tertiary  bases.  In  order  to  avoid  this,  the  alphyl 
iodide,  &c.,  may  be  allowed  to  act  upon  the  acetylated  primary 
bases,  e.g.  acetanilide  [or  upon  their  sodium  compounds  (Hepp}\ 
and  the  resulting  acetyl  compound  hydrolysed : 

C6H6.NH.CO-CH3-f-CH3I  =  C6H6.N(CH3)CO.CH3  +  HI. 

The  secondary  bases  are  separated  from  the  tertiary  by 
treatment  with  nitrous  acid  (see  below,  under  Nitrosamines). 

2.  The  purely  aromatic  secondary  amines  are  obtained  when 
the  primary  arylamines  are  heated  with  their  hydrochlorides : 

NH3. 

Twodiffsrent  aryl  radicals  maybe  introduced,  <?.</.  (C6H6)(CH3» 
C6H4)NH,  phenyl-tolylamine. 

Behaviour. — 1.  The  mixed  secondary  bases  have  strongly- 
marked  basic  properties,  while  the  purely  aromatic  are  feebler 
bases  than  the  primary  arylamines  (cf.  p.  366). 

2.  For  the  migration  of  the  alphyl  group  from  the  side 
chain  into  the  nucleus,  see  p.  369. 

3.  The  hydrogen  of  the  imino-group  is  replaceable  by  an 
alkyl  or  acyl  radical,  and  also  by  potassium  or  sodium: 

(C6H6)2NH  +  CH3I  =  HI  +  (C6H5)2NCH3 

Methyl-diphenylamine. 

(CeH^H  +  CCHg-CO^O  =  CH3.CO2H  +  (C6H5)2N.CO.CH3 

Acetyl-diphenylamine. 

4.  The  secondary  bases  give  neither  the  isonitrile  nor  the 
"mustard  oil"  reaction  (p.  108). 

5.  With  nitrous  acid,  nitrosamines  are  formed  (cf.  p.  108): 

C6H6NHCH3  +  NO.OH  =  H2O  +  C6H6.N(NO).CH3 

Pheuyl-methyl-nitrosamine. 

These  nitrosamines  are  neutral  oily  liquids  insoluble  in 
water,  and  they  regenerate  the  secondary  bases  when  heated 
with  stannous  chloride  or  with  alcohol  and  hydrochloric  acid. 
With  mild  reducing  agents  they  yield  hydrazines. 

They  serve  for  the  preparation  of  the  pure  secondary  bases, 


TERTIARY  MONAMINES  377 

since  they  alone  are  precipitated  by  sodium  nitrite  as  non- 
basic  oils  from  the  acid  solution  of  a  mixture  of  primary, 
secondary,  and  tertiary  bases.  When  such  nitrosamines  are 
digested  with  alcoholic  hydrochloric  acid,  a  molecular  re- 
arrangement takes  place,  and  compounds  of  the  nature  of 
nitroso-dimethyl-aniline  (p.  378)  are  formed,  the  nitroso-group 
becoming  attached  to  a  carbon  atom  of  the  nucleus  (0.  Fischer 
and  Hepp,  B.  19,  2991;  20,  1247): 

C6H6.N(NO).CH3  =  NO.C6H4.NHCH3. 

All  nitrosamines  give  Liebermann's  reaction  (p.  409). 

Methyl  aniline,  C6H5-NHMe,  is  a  colourless  oil  lighter  than 
water.  It  is  a  stronger  base  than  aniline;  its  sulphate  does 
•not  crystallize,  and  is  soluble  in  ether.  With  bleaching-powder 
it  gives  a  brown  coloration. 

(For  the  oxidation  of  ethylaniline,  see  Bamberger,  Abstr. 
1902,  1,  275.) 

Diphenylamine,  NHPh2,  crystallizes  in  colourless  plates, 
melts  at  54°,  distils  at  302°,  and  its  solution  in  sulphuric  acid 
yields  an  intense  blue  colour  with  a  trace  of  nitric  acid  (deli- 
cate test).  It  is  prepared  by  heating  aniline  and  aniline 
hydrochloride  at  210°-240°.  The  nitrosamine,  NPh2-NO, 
forms  yellow  plates  melting  at  6  6 '5°,  and  the  acetyl-deriva- 
tive,  NPho-CO-CHg,  melts  at  103°.  Numerous  nitro-deriya- 
tives  are  Jmown,  e.g.  [C6H2(N02)3]2NH,  which  is  feebly  acidic 
in  properties;  its  ammonium  salt,  C12H4(N02)6N»NH4,  is  the 
dye  aurantia. 

C.  Tertiary  Monamines 

These  also  are  either  purely  aromatic  or  mixed  (alphyl- 
arylamines). 

Modes  of  Fwmation. — 1.  The  latter  are  formed  when  the 
primary  or  secondary  bases  are  alkylated  (cf.  p.  376).  Methyl 
bromide,  iodide  or  sulphate  are  often  used  on  the  small  scale, 
but  on  the  manufacturing  scale  methyl  alcohol  and  hydro- 
chloric acid  under  pressure. 

A  convenient  laboratory  method  is  that  due  to  Noelting 
(B.  1891,  24,  563;  J.  C.  S.  1904,  85,  236).  The  primary 
amine  is  heated  on  the  water-bath  with  a  slight  excess  of  the 
alkyl  iodide  and  sodium  carbonate  solution,  and  in  many  cases 
an  almost  theoretical  yield  of  the  tertiary  amine  is  formed. 
Tertiary  bases  are  also  formed  when  the  quaternary  salts  are 
strongly  heated. 


S?8  XXI.  ARYLAMlNtiS 

2.  Triphenylamine,  a  purely  aromatic  base,  is  formed  by 
the  action  of  bromobenzene  upon  dipotassium-aniline  : 

CCH5NK2  +  2C6H6Br  =  (C6H6)3N  +  2KBr. 

Behaviour.  —  1.  Unlike  the  alphyl-arylamines,  the  purely  aro- 
matic tertiary  amines  are  incapable  of  forming  salts. 

2.  They  do  not  yield  isonitriles  with  CHC13,  isothiocyanates 
with  CS2,  or  acyl  derivatives  with  acid  chlorides,  but  most  of 
them  yield  quaternary  compounds  with  methyl  iodide. 

3.  Nitrous   acid  reacts   with   the   tertiary  aromatic   bases 
(which  thereby  differ  from  the  tertiary  bases  of   the  fatty 
series),  yielding  coloured  nitroso-compounds  which   contain 
the  NO-group  linked  to  the  benzene  nucleus: 


C6H6.N(CH3)2  +  NO.OH  =  NO.C6H4.N(CH3)2  +  H2O. 

2>-N  itroso-d  imethyl-aniline 

Such  nitroso-  derivatives  are,  in  contradistinction  to  the 
nitrosamines  already  mentioned,  converted  into  diamines  on 
reduction,  and  when  hydrolysed  yield  nitroso-phenols. 

4.  The  tertiary  amines,  when  oxidized  with  hydrogen  per- 
oxide, yield  unstable  oxides,  e.g.  dimethyl-phenylamine  oxide, 
CgHg'NMeolO,  feebly  basic  compounds  soluble  in  water,  and 
decomposed  at  high  temperatures.     (B.  1899,  32,  346;  Abstr. 
1901,  1,  200.) 

5.  Tertiary   amines   in   which   the   three   substituents  are 
different,  e.g.  methyl-ethyl-aniline  or  benzyl-phenyl-hydrazine, 
do  not  exist  in  isomeric  forms,  and  cannot  be  resolved  into 
optically  active  components  (Kipping  and  Salway,  J.  C.  S.  1904, 
438;  H.  0.  Jones  and  Millington,  C.  C.  1904,  2,  952).     The 
centres  of  gravity  of  the  nitrogen  atom  and  of  the  three  sub- 
stituents would  therefore  appear  to  lie  in  one  plane. 

Dimethyl-aniline,  C6H5  •  N(CH3)2,  is  an  oil  of  sharp  basic 
odour,  solidifying  in  the  cold;  its  salts  do  not  crystallize  well. 
It  combines  with  methyl  iodide,  even  in  the  cold,  to  the  com- 
pound N(C6H5)(CH3)3I,  phenyl-trimethyl-  ammonium  iodide, 
which  breaks  up  into  its  components  when  distilled.  With 
nitrous  acid  it  yields  ^-nitroso-dimethyl-aniline,  which  crystal- 
lizes in  green  plates,  melting  at  85°;  the  hydrochloride  crys- 
tallizes in  yellow  needles.  When  oxidized  with  permanganate 
the  nitroso-compound  yields  ^-nitro-dimethyl-aniline  (m.-pt, 
162°),  when  reduced  ^-amino-dimethyl-anilme,  and  when  hy- 
drolysed with  alkali  ^-nitroso-phenol  (p.  412)  and  dimethyl- 


THE  QUATERNARY  BASES  379 

amine.  (For  condensations,  see  Malachite  green,  p.  483.) 
Bleaching-powder  colours  dimethyl-aniline  only  a  pale-yellow. 
Dimethyl-aniline  yields  compounds  of  somewhat  complex  com- 
position with  acid  chlorides,  aldehyde,  &c.;  for  example,  tetra- 
methyl-diamino-benzophenone  or,  finally,  methyl  violet  with 
carbonyl  chloride,  leuco-malachite  green  with  benzoic  alde- 
hyde, &c.  Mild  oxidizing  agents,  such  as  chloranil,  convert  it 
into  methyl  violet. 

Diethyl-aniline  boils  at  213°;  its  nitroso-derivative  melts 
at  84°. 

Triphenyl-amine,  NPh3,  melts  at  127°,  and  yields  no  salts. 

D.  The  Quaternary  Bases 

correspond  entirely  with  the  quaternary  bases  of  the  fatty  series. 
Trimethyl-phenyl-ammonium  hydroxide,  C6H5«N(CH3)3«OH, 
for  instance,  is  a  colourless,  strongly  alkaline,  bitter  substance 
which  breaks  up  into  dimethyl -aniline  and  methyl  alcohol 
when  heated.  Most  of  the  tertiary  amines,  however,  which 
contain  substituents  in  the  two  ortho- positions  with  respect 
to  the  alphylated  NH2  group,  are  incapable  of  yielding  quater- 
nary ammonium  salts,  e.g. : 

N(CH3)2 


(E.  Fischer,  B.  1900,  33,  345,  1967).     This  is  an  example  of 
steric  retardation  or  inhibition  (cf.  p.  175). 

The  readiness  with  which  a  given  quaternary  salt  is  formed 
depends  to  a  large  extent  on  (a)  the  order  in  which  the 
radicals  are  introduced,  (6)  the  nature  of  the  alkyl  haloid 
used,  e.g.  chloride  bromide  or  iodide,  the  last  reacting  most 
readily,  (c)  the  solvent  (p.  106),  and  (d)  temperature  (cf.  Wede- 
kind,  A.  1901,  318,  90;  Jones,  B.  A.  Kep.  1904,  179).  It  has 
been  found  that  in  the  preparation  of  phenyl-dimethylethyl 
ammonium  iodide  a  100 -per -cent  yield  is  obtained  when 
methylethyl-aniline  is  combined  with  methyl  iodide,  but  only 
a  15-per-cent  when  dimethyl -aniline  is  combined  with  ethyl 
iodide  under  similar  conditions. 


380  XXI.   ARYLAMINES 

E.  Diamines,  Triamines,  &c. 

Polyamino-derivatives  may  be  obtained  by  reducing  poly- 
nitro-hydrocarbons  or  nitro-amino-compounds,  e.g.  : 

C6H4(N02)2  —  *  C6H4(NH2)2  (plienylene-diamine). 

The  o-  and  ^-diamines  are  best  obtained  from  the  o-  and 
p-nitro-amino-compounds.  Tetramino-  benzene  is  formed  in 
an  analogous  manner  by  reducing  dinitro-m-diamino-benzene. 

A  new  amino-group  can  be  introduced  in  the  ^-position 
into  an  arylamine,  especially  a  secondary  or  tertiary,  such  as 
C6H5»N(CH3)2,  by  first  transforming  the  latter  into  an  azo- 
dye  (e.g.  benzene-azo-dimethyl-aniline,  C6H6-N:N»C6H4»NMe) 
by  coupling  it  with  benzene-diazonium  chloride,  and  decom- 
posing this  by  reduction.  (See  the  Azo-compounds.) 

Diamines  are  also  formed  by  the  reduction  of  the  nitroso- 
compounds  of  tertiary  amines;  amino-dimethyl-aniline,  NH2- 
CglBL-N^Hg)^  from  ^-nitroso-dimethyl-aniline. 

The  polyamines  are  solid  compounds  which  crystallize  in 
plates  and  distil  unchanged,  and  are  soluble  in  warm  water. 
Though  originally  without  colour,  most  of  them  quickly 
become  brown  in  the  air,  their  instability  increasing  with  the 
number  of  amino-groups  present.  In  accordance  with  the 
readiness  with  which  they  are  oxidized,  they  frequently  yield 
characteristic  colorations  with  ferric  chloride,  e.g.  0-phenylene- 
diamine  a  dark-red,  and  1  :  2  :  3-triamino-benzene  a  violet  and 
then  a  brown  colour. 

The  three  isomeric  groups  of  diamines  differ  materially  in 
their  behaviour:  (a)  Ortho-cLLamines.  —  1.  Ferric  chloride  yields 
a  yellowish-red  crystalline  precipitate  of  diamino-phenazine 
hydrochloride  with  a  solution  of  o-phenylene-diamine. 

2.  The  mono-acyl  compounds  of  the  o-diamines  change  into 
derivatives  of  imido-azole  (A.  273,  269),  the  so-called  "JBenz- 
imido-azoles  "  or  "  Anhydro-lases  ",  through  the  formation  of  in- 
tramolecular anhydrides;  thus  o-nitracetanilide,  when  reduced 
with  tin  and  hydrochloric  acid,  yields  methyl-benzimido-azole 
or  phenylene-ethenyl-amidine  (A.  209,  339): 


Compounds  of  this  nature  are  also  obtained   by  heating 
o-diamines  with  acids. 


ACYL  DERIVATIVES  381 

3.  Glyoxal  and  many  of  the  a-diketones  yield  qumoxaline 
and  its  derivatives  with  0-diamines  : 

ON;na""o;c.R 
N;H2    OJC-R 

and  the  a-ketonic  alcohols  react  in  an  analogous  manner,  e.g. 
benzoin  yields  dihydro-diphenyl-quinoxaline. 

4.  Nitrous  acid  converts  the  o-diamines  into  the  so-called 
."  azimido-compounds  ",  compounds  which  contain  three  atoms 
of  nitrogen,  e.g.  0-phenylene-diamine   into  azimido-  benzene 


=  imido-azo-phenylene,  CgH^^N  (B.  9,  219,  1524;  15, 

1878,  2195;  19,  1757). 

(b)  Meta-diamino-bases.  —  1.  These  form  yellow-brown  dyes 
with  nitrous  acid,  even  when  only  traces  of  the  latter  are 
present.     (See  Bismarck  Brown,  p.  401). 

2.  They  yield  azo-dyes  with  benzenediazonium  chloride  (see 
Chrysoidine,  p.  401.) 

3.  With  nitroso-dimethyl-aniline,  or  on  oxidation  together 
with  para-diamines,  blue  colouring-matters  (indamines)  are  ob- 
tained, and  these  when  boiled  yield  red  dyes  (see  Toluylene  red). 

(c)  Para-diamino-compounds.  —  1.  When  warmed  with  ferric 
chloride,  or  better,  with  Mn02  +  H2S04,  quinone,  C6H402  (or 
a  homologue),  is  formed,  and  may  be  recognized  by  its  odour. 

2.  By  oxidizing  para-diamines,  containing  one  amino-group, 
together  with  a  monamine  or  a  meta-diamine,  indamines  are 
produced. 

ACYL  DERIVATIVES  OF  ABYLAMINES.     ANILIDES,  &c. 

Practically  all  primary  and  secondary  arylamines  —  but  not 
tertiary  —  react  with  acids,  or  better,  acid  anhydrides  or  acid 
chlorides,  yielding  acyl  derivatives,  the  most  characteristic 
of  which  are  the  acetyl  derivatives,  e.g.  C6H5  •  NH  •  CO  •  CH3, 
CH3.C6H4.NH.CO.CH3,  (C6H5)2N  •  CO  .  CH3,  &c.  The  acyl 
products  formed  from  aniline  are  termed  anilides  (p.  370),  e.g. 
acetanilide,  benzanilide,  oxanilide;  they  are  really  phenylated 
acid  amides  (see  p.  182  et  seq.),  and  as  such  may  be  hydrolysed, 
although  not  so  readily  as  the  amides,  by  means  of  acids  or 
alkalis,  to  aniline  and  the  corresponding  acid. 

The  dibasic  acids  like  oxalic  acid  can  give  rise  not  merely 
to  anilides,  e.g.  C6H5.NH»CO.CO.NH.C6H5,  oxanilide,  but 


382  XXI.   ARYLAMINES 

also  to  half  anilides,  the  anilic  acids,  which  correspond  with 
the  amic  acids,  e.g.  oxanilic  acid,  C6H5NH  •  CO  •  CO  •  OH. 
These  are  monobasic  acids,  and  can  also  be  hydrolysed  to 
their  components. 

Similarly,  the  toluidines  give  rise  to  toluidides,  e.g.  acetolui- 
dide,  CH3.C6H4.NH.CO.CH3,  the  xylidines  to  xylidides,  &c. 

The  acetyl  derivatives  are  frequently  used  for  the  identi- 
fication of  the  various  primary  and  secondary  arylamines, 
since  they  crystallize  well  and  have  definite  melting-points. 
As  a  rule,  it  is  sufficient  to  mix  the  amine  with  a  slight  excess 
of  acetic  anhydride  and  warm  for  two  minutes,  and  then  to 
pour  into  water.  After  a  short  time  the  solid  (or  oily)  acetyl 
derivative  is  obtained. 

Formanilide,  C6H6»NH«CH:0,  from  aniline  and  formic 
acid,  is  worthy  of  note,  because  its  sodium  salt  reacts  accord- 
ing to  the  formula  C6IL»NNa«CH:0,  but  its  silver  salt  ac- 
cording to  the  formula  C6H5  •  N :  CH  •  0 Ag.  (Cf.  B.  23,  2274, 
Ref.  659.)  The  latter  corresponds  to  those  isomers  of  the 
amides,  the  imido-hydrates  and  imino-ethers  (p.  187). 

Acetanilide,  C6H5«NH«CO'CH3,  is  most  conveniently  pre- 
pared by  boiling  aniline  with  glacial  acetic  acid  for  twenty- 
four  hours.  It  crystallizes  in  beautiful  white  prisms  which  are 
readily  soluble  in  hot  water  or  alcohol,  less  readily  in  ether 
and  benzene.  It  melts  at  115°,  and  boils  at  304°.  In  the 
absence  of  water  it  can  form  a  hydrochloride,  C7H9ON,  HC1. 
Acetanilide  is  used,  under  the  name  of  "  antif ebrine ",  as  a 
medicine  in  cases  of  fever. 

Thio-acetanilide,  C6H5«NH.CS.CH3,  is  formed  when  acet- 
anilide  is  heated  with  P2S5,  and  from  it  imido-thio-com- 
ponnds,  amidines,  &c.,  can  be  prepared.  Methyl-acetanilide, 
C6H5.N(CH8)(CoH30),  is  used  as  a  specific  against  headache. 

Oxanilide,  C6H5  -  NH .  CO .  CO  •  NH .  C6H5,  is  obtained  when 
aniline  oxalate  is  heated  at  160°-180°.  It  melts  at  252°,  boils 
without  decomposition,  and  is  best  hydrolysed  by  fusion  with 
potash. 

The  half  anilide,  oxanilic  acid,  COOH  •  CO  •  NH  •  C6H5,  is 
formed  when  aniline  oxalate  is  heated  at  130°-140°.  It  melts 
at  149°-150°,  is  soluble  in  hot  water,  has  the  properties  of  a 
monobasic  acid,  and  with  phosphorus  pentachloride  yields 
phenyl  carbimide  (phenyl  isocyanate): 

C6H6.NH.CO.OH  —  C6H6.NH.CO.C1  —  C6H5.N:C:O. 
Diacyl  derivatives  of  aniline  and  its  homologues  are  also 


DIACETANILIDE.      PRIMARY   AMINES  383 

known,  e.g.  C6H5  •  N(CO  •  CH3)2,  diacetanilide.  This  is  formed, 
together  with  acetanilide,  when  aniline  is  boiled  for  an  hour 
with  excess  of  acetic  anhydride,  or  when  the  amine  is  heated 
to  a  high  temperature  with  acetyl  chloride.  The  two  may  be 
separated  by  fractional  distillation  under  diminished  pressure. 
The  diacetanilide  crystallizes  in  colourless  prisms,  melts  at 
37°,  and,  unlike  acetanilide,  is  readily  soluble  in  benzene  or  light 
petroleum.  On  hydrolysis  with  dilute  alkali,  one  acetyl  group 
is  split  off  more  readily  than  the  second. 

The  presence  of  one  or  two  substituents  in  the  o-position 
with  respect  to  the  amino-group  of  aniline  facilitates  the  for- 
mation of  diacetyl  derivatives,  e.g.  o-toluidine  yields  a  diacetyl 
derivative  more  readily  than  aniline,  and  s-tribrom-aniline 
yields  a  diacetyl  derivative  with  the  greatest  readiness 
(J.  C.  S.  1901,  533). 

In  nearly  all  those  compounds  of  the  fatty  series  which 
are  amino-  or  imino-derivatives  of  alcohols,  acids,  or  hydroxy- 
acids,  the  unreplaced  ammoniacal  hydrogen  can  be  substituted 
indirectly  either  wholly  or  partially  by  phenyl.  The  number 
of  these  phenylated  (tolylated,  xylylated,  &c.)  compounds  is 
thus  extremely  large.  Among  them  may  be  mentioned: 
Phenyl-glycocoll,  Phenyl-glydne,  C6H5  -  NH .  CH2 .  C02H,  from 
chloracetic  acid  and  aniline;  phenyl-imino-butyric  acid,  CH3« 
C(:NCgH5)-CH.2-C02H,  from  aniline  and  aceto-acetic  ester; 
carbanilide  or  diphenyl-urea,  CO(NHC6H5)2,  from  aniline  and 
carbon  oxy chloride  (cf.  p.  280);  phenyl  isocyanate,  phenyl 
carbimide,  COiN-CgHg,  from  COC12  and  fused  aniline  hydro- 
chloride,  a  sharp-smelling  liquid  exactly  analogous  to  the  iso- 
cyanic  esters — its  vapour  gives  rise  to  tears;  phenyl  isothio- 
cyanate,  C6H5N:CS  (b.-pt.  222°),  a  liquid  possessing  all  the 
characteristics  of  the  mustard  oils  (p.  275);  diphenyl  thio- 
urea,  CS(NHC6H6)2,  from  aniline  and  carbon  disulphide  (forms 
glistening  plates,  melting  at  154°;  it  is  decomposed  into  phenyl 
isothiocyanate  and  aniline  when  hydrolysed  with  concentrated 
HC1). 

PRIMARY  AMINES  WITH  THE  AMINO-GROUP  IN  THE 
SIDE  CHAIN 

These  compounds  resemble  the  primary  alphylamines  much 
more  closely  than  aniline.  As  an  example,  we  have  benzyl- 
amine,  C6H5  •  CH2  •  NH2,  the  amine  corresponding  with 
benzyl  alcohol;  it  is  a  colourless  liquid  which  distils  un- 
changed. The  acetyl  compound,  C6H5.CH2.NH-CO.CH2, 


384.  XXII.   DIAZO-  AND  AZO-COMPOUNDS 

is  formed  by  heating  benzyl  chloride,  CpH5»CH2Cl,  with  acet- 
amide.  Benzylamine  is  formed,  together  with  di-  and  tri- 
benzylamines,  by  the  action  of  alcoholic  ammonia  on  benzyl 
chloride;  it  is  also  readily  obtained  by  reducing  the  phenyl- 
hydrazone  of  benzaldehyde : 

C6H6.CH:N-  NHC6H6   - 
H  H2i    H 

It  may  also  be  prepared  from  benzyl  chloride  and  potassium 
phthalimide  (cf.  p.  465).  Its  behaviour  is  entirely  analogous  to 
that  of  methylamine,  as  the  phenyl  derivative  of  which  it  is 
to  be  regarded.  It  dissolves  in  water,  and  the  solution  thus 
formed  is  alkaline.  Conductivity  determinations  show  that  it 
is  about  as  strong  a  base  as  ammonia,  and  thus  differs  materi- 
ally from  aniline. 

It  possesses  all  the  characteristic  properties  of  a  primary 
amine,  but  as  the  NH2  is  attached  to  a  side  chain  and  not  to 
the  benzene  nucleus  it  cannot  be  diazotized,  and  on  treatment 
with  nitrous  acid  it  immediately  yields  benzyl  alcohol. 


XXII.   DIAZO-  AND  AZO-COMPOUNDS; 
HYDEAZINES 

A.  Diazo-eompounds 

The  primary  arylamines  differ  characteristically  from  the 
primary  alphylamines  in  their  behaviour  towards  nitrous  acid. 
The  latter  are  converted  into  alcohols  without  the  formation 
of  intermediate  products  (cf.  p.  108): 


The  aromatic  amines  can  undergo  an  analogous  transfor- 
mation; but  if  the  temperature  is  kept  sufficiently  low,  well- 
characterized  intermediate  products,  the  so-called  diazo-eom- 
pounds  or  diazonium  salts,  e.g.  benzene  diazonium  chloride, 
C6H5«N2C1,  are  obtained,  which  are  of  especial  interest  both 
scientifically  and  technically  (cf.  Azo-dyes,  p.  389).  They  were 
discovered  by  P.  Griess  in  1860,  and  were  carefully  investigated 
by  him  (A.  121,  257;  137,  39). 

The  diazo-compounds  are  usually  divided  into  (1)  the  diazo- 

r^  FT 
nium  salts,  e.g.     6p£>NjN,  compounds  which  are  analogous 


DIAZONIUM   COMPOUNDS  <385 

to  ammonium  salts;  (2)  the  true  diazo-compounds,  which  con- 
tain the  grouping  •  N :  N  • . 

I.  Diazonium  Compounds, — The  diazonium  salts,  as  a  rule, 
#re  not  obtained  in  the  solid  state,  as  they  themselves  are  of 
little  commercial  value,  but  are  of  importance  as  intermediate 
products  in  various  decompositions. 

Solutions  are  usually  prepared  by  the  addition  of  an 
aqueous  solution  of  sodium  nitrite  to  a  solution  of  the  amine 
in  an  excess  of  the  requisite  acid  (V.  Meyer}.  The  essentials 
are — (1)  The  solution  must  be  kept  cool,  at  0°  or  only  a  few 
degrees  above,  otherwise  a  phenol  is  formed  and  nitrogen 
evolved.  (2)  An  excess  of  acid  must  be  used,  otherwise 
diazo-amino-compounds  are  formed.  (3)  As  a  rule,  it  is 
advisable  not  to  use  an  excess  of  nitrous  acid.  This  is 
avoided  by  testing  for  free  nitrous  acid  by  means  of  potassium 
iodide  starch  paper. 

This  conversion  of  amino-  into  diazo-compounds  is  termed 
"  diazotizing  ". 

The  crystalline  salts,  e.g.  benzene-diazonium  chloride,  may 
be  obtained  by  adding  concentrated  hydrochloric  acid  to  an 
alcoholic  solution  of  aniline  hydrochloride,  and  then  amyl 
nitrite  (Knoevenagel).  They  may  also  be  obtained  by  the 
addition  of  alcohol  and  ether  to  their  aqueous  solutions. 

Constitution. — The  N.2X  group  can  be  attached  to  only  one 
carbon  atom  of  the  benzene  nucleus,  since  (1)  when  the  salts 
undergo  decomposition  the  products  formed  contain  groups, 
e.g.  Cl,  OH,  CN,  &c.,  which  are  attached  to  a  single  carbon 
atom;  (2)  penta- substituted  anilines,  e.g.  S03H-C6Br4»NH2, 
can  be  diazotized,  hence  Griess'  formulae,  e.g.  C6H4N2,  HC1, 
where  the  diazo-radical  replaces  two  hydrogen  atoms  of  the 
nucleus,  are  untenable. 

For  many  years  the  constitutional  formula  given  to  these 
compounds  was  that  suggested  by  KekuU,  viz.  C6H5*N:N»C1, 
for  the  chloride;  this  represents  them  as  analogous  to  the 
azo-compounds.  This  formula  readily  explains  the  reduction 
of  the  diazonium  salts  to  hydrazines,  CVH5NH«NH2,  and  their 
conversion  into  azo-dyes,  e.g.  C6H5  •  N :  N  •  C6H4OH.  Within  the 
last  few  years  a  constitutional  formula  which  was  suggested  by 
Blomstrand  in  1875  has  become  generally  accepted.  This  repre- 
sents the  molecule  of  a  diazonium  salt  as  containing  a  quinque- 

O  TT 
valent  nitrogen  atom,  e.g.     6Q-£>N:N.     The  chief  arguments 

in  favour  of  the  Blomstrand  formula  are  briefly: 

(B480)  2P, 


386  XXII.    DIAZO-  AND   AZO-COMPOtTNDS 

• 

1.  It  indicates  the  resemblance  between  the  diazonium  and 
ammonium  salts,  as  both  thus  contain  quinquevalent  nitrogen : 

and 

The  resemblance  between  the  two  groups  of  compounds  is 
marked.  The  diazonium  salts  are  colourless  crystalline  com- 
pounds readily  soluble  in  water;  those  derived  from  strong 
acids,  e.g.  the  chlorides,  nitrates,  and  sulphates,  are  neutral  in 
solution,  cf.  NH4C1;  whereas  those  derived  from  feeble  acids, 
e.g.  carbonic  acid,  are  partially  hydrolysed  in  aqueous  solution, 
and  hence  give  an  alkaline  reaction,  cf.  Na.,C08  or  (NH4)2C03. 
In  addition  they  form  sparingly  soluble  platinichlorides, 
(C6H5N2)2PtCl6,  and  aurichlorides,  C6H5N2AuCl4,  comparable 
with  the  ammonium  compounds.  The  aqueous  solutions  of 
the  salts  are  ionized  to  much  the  same  extent  as  the  corre- 
sponding quaternary  ammonium  salts.  This  resemblance  of 
the  diazonium  ions  to  the  quaternary  ammonium  ions  is 
further  established  by  a  comparison  of  migration  values. 
The  free  base,  benzene -diazonium  hydroxide,  corresponding 
with  ammonium  hydroxide,  is  obtained  by  the  action  of  moist 
silver  oxide  on  the  chloride;  it  dissolves  readily  in  water, 
yielding  strongly  alkaline  solutions,  but  is  very  unstable,  and 
gradually  decomposes.  When  neutralized  with  acids,  it  yields 
the  above-mentioned  diazonium  salts. 

2.  The  conversion  of  aniline  and  its  homologues  into  diazo- 
nium salts  is  rendered  somewhat  more  simple  by  such  a  for- 
mula: 

HO 


3.  The  elimination  of  nitrogen  and  the  formation  of  mono- 
Bubstituted  compounds,  e.g.  C6H5-OH,  C6H6Br,  &c.,  is  readily 
explicable: 


Cain  (J.  C.  S.  1907,  91,  1049)  has  suggested  a  new  consti- 
tutional formula  for  diazonium  salts,  e.g.  benzene-diazonium 
chloride, 

:N.C1 


-N 
is  claimed  that  the  double  linkage  between  nitrogen  and 


REACTIONS  OP  DIAZONIUM   SALTS  387 

carbon  atom  of  the  benzene  nucleus  is  more  in  harmony  with 
the  readiness  with  which  the  nitrogen  is  eliminated  from  the 
molecule.  It  also  accounts  for  the  fact  that  in  a  ^-diamine 
only  one  amino-group  can  be  diazotized. 

Reactions.  —  1.  The  reaction  characteristic  of  the  diazonium 
salts  is  the  readiness  with  which  nitrogen  is  eliminated  and 
monovalent  groups  introduced  into  the  molecule  in  place  of 
the  N2X  radical,  and  for  this  reason  the  diazonium  compounds 
are  frequently  made  use  of  in  the  laboratory  for  the  prepara- 
tion of  various  substituted  benzene  derivatives.  As  examples 
of  this  type  of  reaction,  we  have  — 

(a)  Replacement  of  N2X  by  OH.  —  An  aqueous  solution  of 
a  diazonium   salt,   especially  one  containing   sulphuric  acid, 
evolves  all  its  nitrogen  in  the  form  of  gas  when  warmed,  and 
a  phenol  is  formed  : 

|N:N  =  CflH6.OH  +  N2-f  HCI. 

This  reaction,  which  is  of  very  universal  application,  there- 
fore allows  of  the  exchange  of  NH2  for  OH.  The  only  excep- 
tions appear  to  be  those  salts  containing  numerous  negative 
substituents  in  the  benzene  nucleus,  e.g.  C6H2Br3  •  N2C1. 

For  the  effect  of  light  on  the  decomposition  of  solutions 
of  diazonium  salts,  see  Orton,  Coates,  and  Burdett,  P.  1905, 
168. 

(b)  Replacement  by  H.  —  When  diazonium-compounds,  either 
in  the  solid  state  or  dissolved  in  concentrated  sulphuric  acid, 
are  heated  to  boiling  with  absolute  alcohol,  the  diazo-group  is 
generally  replaced  by  hydrogen.     In  this  reaction  the  alcohol 
gives  up  two  hydrogen  atoms,  and  is  oxidized  to  aldehyde  : 


This  affords  a  simple  method  for  the  replacement  of  NH0 
by  H. 

Instead  of  this  reaction,  there  occurs  in  many  cases  an  ex- 
change of  the  diazo-group  for  the  ethoxy-radical,*0'C2H5,  with 
the  formation  of  ethyl  ethers  of  phenols;  thus  from  chlorinated 
toluidines  ethyl  ethers  of  chloro-cresols  are  formed,  and  not 
chloro-toluenes  (B.  17,  2703;  22,  Ref.  658;  34,  3337). 

Under  certain  conditions  stannous  chloride  in  alkaline  solu- 
tion acts  in  an  analogous  manner  (B.  22,  Ref.  741),  while 
under  others  it  gives  rise  to  hydrazines  (p.  397).  In 


388  XXII.    DIAZO-   AND  AZO-COMPOUNDS 

manner  NH2  may  be  replaced  by  H,  by  first  converting  an 
amino-compound  into  a  hydrazine,  and  then  decomposing  the 
latter  with  CuS04  (Baeyer,  B.  18,  89). 

(c)  Replacement  by  Halogen  —  Sandmeyer's  Reaction.  —  When  a 
diazonium-compound  is  warmed  with  a  concentrated  solution 
of  cuprous  chloride  in  hydrochloric  acid,  the  diazo-group  is 
replaced  by  chlorine  (Sandmeyer,  B.  17,  1633;  23,  1218,  1628; 
A.  272,  143).  The  same  reaction  takes  place  on  distilling  the 
diazonium  platinichloride  with  soda,  and  sometimes  on  simply 
treating  the  diazo-compound  itself  with  fuming  hydrochloric 
acid,  or  with  hydrochloric  acid  in  presence  of  copper  dust 
(Gattermann)  : 


Warming  with  cuprous  bromide  yields,  in  the  same  way,  a 
bromo-derivative  (Sandmeyer,  B.  18,  1482),  and  treatment  with 
hydriodic  acid  or  potassium  iodide  an  iodo-compound  : 


2C6H6.N2.C1  +  CuJBro  =  2C6H5Br  +  Cu2CL  +  N2; 
C6H6  •  N2  •  Cl  +  KI         =  CCH5I  +  KC1  +  N2. 

The  ammo-group  may  further  be  exchanged  for  bromine  by 
boiling  the  diazonium  perbromides  (see  Benzene-diazonium  per- 
bromide)  with  absolute  alcohol. 

(d)  ^Replacement  by  »C]N.  —  This  is  accomplished  by  adding 
the  diazotized  solution  to  a  warm  solution  of  potassium  cuprous 
cyanide  : 

C6H6.N2C1  —  C6H6N2CN  —  C6H5-CN. 

This  reaction  is  of  importance,  as  the  product  obtained  is  a 
nitrile,  and  can  be  hydrolysed  to  an  acid. 

(e)  Phenyl  sulphide  is  formed  by  the  action  of  hydrogen 
sulphide  on   benzene-diazonium   chloride  (cf.  B.   15,    1683); 
nitro-  benzene   is   formed   by  the   action  of   nitrous  acid   in 
presence  of  cuprous  oxide;   benzenesulphonic  acid  from  sul- 
phurous acid;  phenyl  thiocyanate  from  thiocyanic  acid;  and 
phenyl  cyanate  from  cyanic  acid,  &c.  (cf.  B.  23,  738,  1218, 
1454,  1628;  25,  1086;  26,  1996). 

(/)  When  oxidized  in  alkaline  solution,  benzene-diazonium 
hydroxide  yields  —  together  with  other  products  —  nitroso-ben- 
zene  (p.  365),  and  much  benzene-diazoic  acid,  C6H5'N  -NO- 
OK,  or  its   isomeride,    phenyl  -  nitramine,   C6H5»NH«NO,, 
(m.-pt.  46°;  explodes  at  98°)  (see  B.  26,  471;  2?,  584,  915). 


REACTIONS  OF  DIAZONIUM  SALTS  389 

2.  When  a  solution  of  a  diazonium  compound  reacts  with  a 
primary  or  secondary  amine,  or  when  nitrous  acid  acts  upon 
such  an  amine  in  the  absence  of  free  mineral  acid,  diazo- 
amino-compounds  are  formed,  and  these  readily  change  into 
amino-azo-compounds  : 


Diazo-amiuo-benzene. 

3.  Azo-dyes.  —  The  diazonium  salts  readily  react  with  ter- 
tiary amines   or   with  phenols,  yielding  derivatives  of   azo- 
benzene,  e.g.  : 

C6H6.N2C1  +  C6H6N(CH3)2  =  HC1  +  C6H6.N:N.C6H4.N(CH3)2 

Dirnethyl-amino-azobenzene. 

C6H6.N2C1  +  C6H5.OH         =  HC1  +  C6H5-N:N.C6H4.OH 

Hydroxy-azobenzene. 

Such  derivatives  possess  basic  or  acidic  properties,  are 
usually  coloured  yellow,  red,  or  brown,  and  are  known  as 
azo-dyes. 

The  formation  of  such  an  azo-dye  is  largely  made  use  of  as 
a  test  for  a  primary  aromatic  amine  with  the  NH2  in  the 
nucleus.  The  amine  is  dissolved  in  acid,  diazotized,  and  then 
mixed  with  an  alkaline  solution  of  a  phenol  (preferably 
/3-naphthol),  when  an  orange-red  dye  is  precipitated.  The 
process  is  commonly  spoken  of  as  the  "coupling"  up  of  a 
diazonium  salt  with  an  amine  or  a  phenol. 

It  has  been  proposed  to  use  diazo-compounds,  sensitive  to 
light,  in  photography  (B.  23,  3131;  34,  1668). 

4.  The  diazonium  salts  react  in  alkaline  solution  with  com 
pounds  containing  the  grouping  •CH2'CO»,  yielding  azo-com- 
pounds  or  phenylhydrazones,  e.g.  : 

PIT    rn  PTT    rn  ^ 
/H3C 

Cf.  B.  1888,  21,  1697.  For  the  azo  or  hydrazone  constitution 
of  such  compounds,  compare  Auwers  (Abstr.  1908,  i,  477; 
1911,  i,  168,  585). 

Benzene-diazonium  perbromide,  C6H5  •  N2Br,  Br2,  is  a  dark- 
brown  oil,  solidifying  to  yellow  crystalline  plates,  and  is  pre- 
pared by  the  addition  of  HBr  or  KBr  and  bromine  water  to 
diazonium  salts.  Two  of  its  atoms  of  bromine  are  only  loosely 
linked.  Ammonia  converts  it  into  benzene-diazo-imide,  which 


390  XXII.   DlAZO-  AND  A20-COMPOtJN&S 

is  to  be  regarded  as  the  phenyl  derivative  of  hydrazoic  acid, 
N3H,  thus: — 

C6H6  •  N(Br) :  N  +  Br2  =  C6H6  •  NBr2 :  NBr  [Beuzene-diazonium  perbromide]. 

a  XT 
[Benzene-diazo-imide]. 

In  accordance  with  this,  dinitro-benzene-diazo-imide  (from 
dinitro-aniline)  is  decomposed  by  alcoholic  potash  into  dinitro- 
phenol  and  hydrazoic  acid — a  method  of  obtaining  this  latter 
substance  by  means  of  organic  compounds  (see  p.  298). 

II.  Diazo- compounds. — These  contain  the  grouping  R-N: 
N«X,  where  R  =  an  aryl  radical  and  X  an  acid  radical  or 
OH  or  OK.  When  a  benzene-diazonium  salt  is  mixed  with 
an  excess  of  alkali,  a  potassium  salt,  normal  potassium  diazo- 
benzene  oxide,  C6H5N2OK,  is  precipitated.  It  crystallizes  in 
white  plates,  and  can  be  quantitatively  converted  into  ben- 
zene-diazonium chloride;  it  yields  ethers,  and  on  oxidation 
gives  nitroso-benzene  and  benzene-diazoic  acid: 

C6H6.N:N<°H    or    CflH^NH-NOj, 

The  acid,  C6H5N2OH,  which  corresponds  with  the  potassium 
salt,  is  not  known  in  a  pure  form.  When  the  normal  potas- 
sium salt  is  heated  with  concentrated  potash  at  130°-135°,  it 
is  transformed  into  potassium  isodiazo-benzene  oxide  (Schraube 
and  Schmidt,  B.  1894,  27,  520).  When  this  is  acidified  with 
acetic  acid,  the  free  hydroxide  is  obtained  as  a  colourless  oil 
which  is  very  unstable. 

Similar  normal  and  isopotassium  derivatives  have  been  ob- 
tained from  other  diazonium  salts,  and  it  has  been  found  that 
the  presence  of  negative  radicals  (Br,  N02)  facilitates  the  for- 
mation of  the  iso-compound, — in  fact  to  such  an  extent  that 
certain  diazonium  salts,  when  added  to  an  alkali,  immediately 
yield  the  isodiazo-compounds.  Considerable  controversy  has 
taken  place  regarding  the  constitutional  formulae  of  these  two 
groups  of  compounds.  At  one  time  the  isodiazo-oxides  were 
regarded  as  derivatives  of  phenyl-nitrosamine,  viz.  C6H5-NK» 
NO,  and  the  normal  compounds  as  true  diazo-oxides,  C6H6« 
N:N»OK.  The  researches  of  Hantzsch  have  proved  that  the 
two  compounds  are  very  similar  as  regards  chemical  properties. 
For  example,  both  "couple"  with  alkaline  solutions  of  phenols, 
yielding  azo-dyes  (p.  389),  but  as  a  rule  the  normal  more 
readily  than  the  iso-compounds.  Both  compounds,  on  reduc- 


STEREO-ISOMERIC  DIAZO-HYDROXtDES  391 

tion  with  sodium  amalgam  in  the  presence  of  a  large  excess  of 
alkali,  yield  phenyl-hydrazine,  and  both  compounds,  on  oxi- 
dation in  alkaline  solution,  yield  potassium  benzene-diazoate, 
C6H5  •  N :  NO  •  OK.  Similarly,  both  compounds  yield  the  same 
benzoyl  derivative  by  the  Schotten-Baumann  method.  Hantzsch 
draws  the  conclusion  that  the  two  compounds  are  structurally 
identical  and  stereo-isomeric.  As  the  w-diazo-oxide  can  be  syn- 
thesised  by  the  action  of  hydroxylamine  on  nitroso-benzene  in 
alkaline  solution  (B.  38,  2056): 


N.OH  =  H20  +  C6H6.N:N-OH, 

it  is  probable  that  both  normal  and  iso-compound  are  true 
diazo-derivatives,  and  that  they  are  stereo-isomeric  in  much 
the  same  manner  as  the  oximes  (p.  138).  According  to 
Hantzsch,  the  normal  compound  has  the  syn-  and  the  iso-  the 
<w&'-configuration  : 

C6H5-N  C6H6.N 

KO-N  N-OK, 

Potassium  benzene  syn  diazo-oxide  anti 

as  the  normal  compounds  evolve  nitrogen  very  readily,  whereas 
the  iso-compotinds  are  more  stable.  (Ber.  1894,  27,  1702; 
1895,  28,  676,  1734;  36,  4054;  37,  1684.) 

The  isodiazo-oxides  can  almost  undoubtedly  react  as  tauto- 
meric  compounds,  viz.  as  nitrosamine  derivatives,  C6H5-NK« 
NO,  since  the  potassium  salt  yields  an  N-ether,  C6H5'NEt-NO, 
whereas  the  silver  salt  yields  an  O-ether,  C6H5  •  N :  N  •  OEt. 
Bamberger  has  suggested  that  the  normal  diazo-oxides  may 
have  a  diazonium  constitution  C6H5«N(OK)jN,  whereas  the 
iso-compound  has  the  diazo-constitution  C6Hg«N:N«OK;  but 
Hantzsch  has  pointed  out  that  the  diazonium  hydroxides, 
from  which  the  true  diazonium  salts  are  formed,  must  be 
extremely  strong  bases,  and  could  not  possibly  therefore  pos- 
sess sufficiently  acidic  properties  to  give  rise  to  stable  potas- 
sium salts  which  are  only  partially  hydrolysed  in  aqueous 
solution. 

Certain  diazo-hydroxides,  R«N2»OH,  have  been  isolated  as 
colourless  solids  with  acidic  properties ;  the  majority,  however, 
are  extremely  unstable,  and  pass  over  into  the  isomeric  nitros- 
amines  R-NH-NO,  yellow  compounds  with  neutral  properties 
(B.  35,  2964;  36,  4054;  37,  1084). 

Corresponding  with  the  normal  and  isodiazo-oxides,  Hantzsch 


392  XXII.   DIAZO-  AND  AZO-COMPOUNDS 

has  discovered  two  groups  of  sulphonates  and  of  cyanides, 
which  he  also  regards  as  being  stereo-isotneric  in  the  same 
sense,  e.g.: 

E-N  K-N 


In  the  case  of  j0-anisidine,  evidence  of  the  existence  of  three 
isomeric  diazo-cyanides  has  been  obtained.  The  one  is  colour- 
less and  is  an  electrolyte,  and  hence  is  regarded  as  the  diazo- 
nium  salt,  OMe-C6H4-N(CN)jN;  the  other  two  are  reddish- 
coloured  solids  and  non-electrolytes.  The  syw-compound  is 
unstable,  and  melts  at  51°;  it  gradually  passes  over  into  the 
more  stable  an  ^'-compound,  which  melts  at  121°. 

It  is  probable  that  when  a  syn  diazo-cyanide  is  dissolved  in 
water  it  is  largely  transformed  into  the  ionized  diazonium 
cyanide  : 


Compare  also  Armstrong  and  JRobertson,  J.  C.  S.  1905,  1280; 
Hantzsch,  P.  1905,  287.  An  account  of  the  chemistry  of  diazo- 
compounds  will  be  found  in  B.  A.  Rep.  1902,  181  (G.  T.  Morgan), 
and  in  Ahrens  Sammlungt  1902,  8,  pp.  1-82  (Hantzsch). 

B.  Diazo-amino-eompounds 

The  diazo-amino-compounds  are  pale-yellow  crystalline  sub- 
stances which  are  stable  in  the  air,  and  do  not  combine  with 
acids.  They  are  obtained  by  the  action  of  a  primary  or 
secondary  amine  on  a  diazonium  salt,  and  also  when  nitrous 
acid  reacts  with  a  free  primary  aromatic  amine  instead  of  with 
its  hydrochloride,  probably  : 

C6H5NH2-f-O:N.OH  =  C6H6-N:N.OH  +  H2O  and 
C6H5.N:N.OH  +  C6H6NH2  =  C6H6.N:N.NHC6H6  +  H2O. 

Diazo-amino  compounds  have  been  synthesised  by  the  action 
of  Grignard  compounds  on  alkyl  or  acyl  derivatives  of  hydra- 
zoic  acid,  and  decomposing  the  products  with  water: 

RN3  +  B'Mgl  —  RN(MgI)-N:NR' 
RN(MgI).N:NR'  +  H2O  —  R-NH-NiN-R'  +  Mgl-OH 

In  this  manner  not  merely  aromatic  but  aliphatic  aromatic 


blAZO-AMINO-COMPOtJNDS  393 

Compounds  of  the  types  C6H6-NH.N:N.CH3  and  C6H5«CH2- 
NH  •  N :  N  •  CH3  have  been  prepared. 

Reactions. — 1.  They  are  not  bases,  and  hence  do  not  form 
salts  with  acids. 

2.  They  behave  in  much  the  same  way  as  the  diazo-com- 
pounds,  since  they  are  usually  decomposed  in  the  first  instance 
into  their  components,  a  diazonium  salt  and  an  amine,  the 
former  then  entering  into  reaction.      Thus  diazo-amino-ben- 
zene,    for   example,   yields   phenol  and   aniline  when   boiled 
with  water   or   hydrochloric   acid,    while   with   hydrobromic 
acid   it   gives   bromobenzene   and    aniline.      These   reactions 
are  easy  to  recognize  from  the  accompanying  evolution  of 
nitrogen. 

3.  By  the  renewed  action  of  nitrous  acid  in  acid  solution 
they  are  completely  transformed  into  diazonium  salts: 

C6H6.N2.NH.C6H5  +  NO2H  +  2HC1  =  2C6H5.N2.C1  +  2H2O. 

4.  Most  of  them  readily  undergo  molecular  transformation 
into  the  isomeric  amino-azo-compounds  (KekuU): 

C6H6.N:N-NH/       \H  —  C6H6.N:N/ 

This  molecular  rearrangement  takes  place  most  readily  in 
presence  of  an  amine  hydrochloride,  which  acts  as  a  catalytic 
agent.  The  amino-group  always  takes  up  the  para-position 
with  regard  to  the  azo-group  (»N:N«)  if  this  is  free.  If,  how- 
ever, this  is  already  substituted,  as  in  the  diazo-amino-com- 
pound  from  |?-toluidine,  then  the  transformation  occurs  much 
more  slowly,  and  the  NH2  takes  up  the  o-position  with  respect 
to  the  •  N :  N  •  group.  The  velocity  of  transformation  has  been 
investigated  by  H.  Goldschmidt,  and  the  reaction  has  been 
shown  to  be  unimolecular.  Only  a  relatively  small  amount 
of  aniline  salt  is  required,  and  the  velocity  is  proportional  to 
the  strength  of  the  acid,  the  aniline  salt  of  which  is  used  (B. 
1896,  29,  1899).  For  similar  transformations,  see  Benzidene 
(p.  395)  and  Azoxy-benzene  (p.  395). 

5.  The   imino- hydrogen  of   the  diazo-amino-compounds  is 
replaceable  by  metallic  radicals,  and  also  by  acyl  groups. 

Constitution. — By  the  action  of  benzene-diazonium  chloride 
upon  ^-toluidine,  "  diazo-benzenef>-toluidide "  is  formed,  and 
would  appear  to  possess  the  formula: 

(I). 


394  XXII.   DIAZO-  AND  AZO-COMPOUNDS 

But  the  same  compound  is  also  obtained  from  a  mixture 
of  ^-toluene-diazonium  chloride  and  aniline,  a  reaction  which 
would  indicate  its  constitution  to  be: 

C6H6.NH.N:N.CVH7    (II). 

It  is  all  the  more  difficult  to  decide  which  of  these  two 
formulae  is  the  right  one,  from  the  fact  that  most  of  those 
"  mixed  diazo-amido-compounds  "  react  as  if  they  had  both  of 
the  above  constitutions.  Thus,  when  the  compound  just  men- 
tioned is  boiled  with  dilute  sulphuric  acid,  it  yields  not  only 
phenol  and  ^-toluidine  (according  to  I),  but  also  aniline  and 
^?-cresol  (according  to  II).  Such  diazo-ami  no-compounds  are 
thus  typical  tautomeric  substances.  (Cf.  e.g.  B.  19,  3239;  20, 
3004;  21,  548,  1016,  2557;  J.  C.  S.  1889,  55,  412,  610,  &c.) 

Diazo-amino-  benzene,  C6H5  •  N  :  N  •  NHC6H5  (Griess),  is 
usually  prepared  by  adding  NaN02  (1  mol.)  to  the  solution 
of  aniline  (2  mols.)  in  HC1  (3  mols.),  and  saturating  with 
sodium  acetate  (B.  1884,  17,  641;  1886,  19,  1952).  It  crystal- 
lizes in  bright-yellow  lustrous  plates  or  prisms,  is  insoluble  in 
water,  but  readily  soluble  in  hot  alcohol,  ether,  and  benzene, 
melts  at  98°,  and  is  far  more  stable  than  the  diazo-compounds. 

C.  Azo-compounds,  and  Compounds  intermediate 
between  the  Nitro-  and  Ammo-compounds 

While  the  reduction  of  nitro-compounds  in  acid  solution  leads 
to  the  aromatic  amines,  the  use  of  alkaline  reducing  agents, 
such  as  sodium  amalgam,  zinc  dust  and  caustic  soda,  and  also 
potash  and  alcohol,  gives  rise  for  the  most  part  to  intermediate 
products,  the  azoxy-,  azo-,  and  hydrazo-compounds  : 

C6H5.N02  C6H6.iST.N.C6H5  C6H5.N:N.C6H5 

Nitro-benzene  \/  Azo-benzene 


Azoxy-benzene 
CCH6NH  •  NHC6H5  C6H6  .  NH2; 

Hydrazo-benzene  Aniline 

and   reduction   in   neutral   solution  yields   pheriyl-hydroxyl- 
amines,  C6H5-NH.OH. 

Of  these  the  azo-compounds  are  the  most  important 


1.  AZOXY-COMPOUNDS 


The  azoxy-compounds  are  mostly  yellow  or  red  crystalline 
substances  which  vare   obtained   by   the  action   of   alcoholic 


HYDRAZO-COMPOtlNDS  396 

potash,  and  especially  of  potassium  methoxide  (B.  15,  865), 
upon  the  nitro-compounds.  Many  of  them  may  also  be 
obtained  by  the  oxidation  of  azo-compounds.  They  are  of 
neutral  reaction,  and  are  very  readily  reduced  to  azo-com- 
pounds. 

Azoxy -  benzene,  (C6H5)2N20  (Zinin),  forms  pale -yellow 
needles  melting  at  36°,  is  insoluble  in  water,  but  dis- 
solves readily  in  alcohol  and  ether.  Concentrated  sulphuric 
acid  transforms  it  into  the  isomeric  ^?-hydroxy-azo-benzene, 
CGH5N:N.C6H4.OH. 

2.  HYDRAZO-COMPOUNDS 

These  are  colourless  crystalline  neutral  compounds,  and, 
like  the  azo-compounds,  cannot  be  volatilized  without  decom- 
position; e.g.  hydrazo- benzene  decomposes  into  azo-benzene 
and  aniline  when  heated.  They  are  obtained  by  the  reduction 
of  azo-compounds  with  ammonium  sulphide  or  zinc  dust  and 
alkali,  or  by  sodium  hyposulphite.  Oxidizing  agents,  such  as 
ferric  chloride,  readily  transform  them  into  azo-compounds,  a 
reaction  which  also  occurs  when  the  hydrazo-compounds  are 
exposed  to  the  air.  Stronger  reducing  agents,  e.g.  sodium 
amalgam,  convert  them  into  amino-compounds. 

Strong  acids  cause  them  to  change  into  the  isomeric  deriv- 
atives of  diphenyl  (p.  472);  thus  from  hydrazo-benzene  and 
hydrochloric  acid  we  obtain  benzidine  hydrochloride  (the 
hydrochloride  of  ^/-diamino-diphenyl,  p.  472): 

— >  NIL, 

This  rearrangement  is  typical,  and  is  often  observed  in  the 
case  of  aromatic  compounds.  It  may  be  regarded  as  the 
shifting  or  wandering  of  a  radical — in  this  case  the  relatively 
complex  CgH5«NH — from  attachment  to  the  side  chain  to 
direct  attachment  to  the  benzene  nucleus,  or,  in  other  words, 
the  NH'CgHg  group  exchanges  place  with  the  hydrogen  atom 
in  the  ^-position  in  the  nucleus: 


396  XXII.   DIAZO-  AND  AZO-COMPOUNDS 

The  operation  is  repeated, 


and  j^'-diamino-diphenyl  is  formed. 

Other  well-known  examples  of  this  are  the  transformation  of 
methyl-aniline  or  dimethyl-aniline  into  o-toluidine  and  xylidene, 
and  ultimately  into  mesidene  (Hofmann,  p.  368);  the  transforma- 
tion of  N-brominated  amines  or  anilides,  e.g.  C6H5  •  NBr  •  COCH3 
into  C6H4Br-NH.COCH3  (Chattaway  and  Orion,  p.  370),  of  dia- 
cetylated  amines,  C6H5»N(COCH3)2,  into  ketonic  substances, 
CH3  •  CO  -  C6H4  •  NH  -  CO  •  CH3  (Chattaway,  J.  C.  S.  1 904,  386,  589, 
1663),  of  phenyl-hydroxylamine  into  ^-amino-phenol  (p.  395), 
and  of  diazo-amino-benzene  into  amino-azo-benzene  (p.  391). 

This  molecular  rearrangement  does  not  take  place  if  the 
hydrogen  which  occupies  the  para-position  to  the  imino-group 
is  replaced  by  other  groups.  In  such  cases  a  partial  re- 
arrangement only  occurs,  and  derivatives  of  diphenylamine 
are  formed  (B.  25,  992,  1013,  1019);  thus  ^-hydrazo-toluene, 
CH3  •  C6H4 •  NH  •  NH  •  C6H4  -  CH3,  yields  o-amino-di-^-toly lamine, 

CH8.C6H4.NH-C6H8<0|k     (Cf.  Jacobson,  B.  1893,  26,  700; 

1898,  31,  890;  A.  1895,  2837,  98.) 

Hydrazo-benzene,  sym.-Diphenyl-hydrazine,  C6H5  •  NHe  * :  I 1  • 
CgH5  (Hofmann),  forms  colourless  plates  of  camphor- like 
odour,  which  are  only  slightly  soluble  in  water,  but  dissolve 
readily  in  alcohol  and  ether;  m.-pt.  131°.  The  imino-hydrogen 
atoms  are  replaceable  by  acetyl-  or  nitroso-groups. 

3.  AZO-COMPOUNDS 

The  azo-compounds  are  red  or  yellowish -red,  crystalline, 
neutral  substances,  insoluble  in  water,  but  soluble  in  alcohol; 
some  of  them  may  be  distilled  without  change.  Azo-benzene 
itself  (benzene-azo-benzene,  C6H5«N:N«C6H5)  crystallizes  in 
large  red  plates,  melts  at  68°,  and  distils  at  293°.  Oxidizing 
agents  convert  them  into  azoxy-,  and  reducing  agents  into 
hydrazo-  or  amino-compounds.  Chlorine  and  bromine  act  as 
substituents. 

The  so-called  "mixed"  azo-compounds,  which  contain  both 


ft  PHENYL-HYDROXYLAMINE  397 

an  alphyl  and  an  aryl  radical,  are  also  known,  e.g.  azo-phenyl- 

ethyl,  C6H5.N:N.C2H5,  a  bright-yellow  oil  (B.  1897,  30,  793). 

Modes  of  Formation.  —  1.  By  the  cautious  reduction  of  nitro- 

or  azoxy-compounds,  e.g.  by  means  of  sodium  amalgam  or  of 

an  alkaline  solution  of  stannous  oxide  (B.  18,  2912).     2.  By 

distilling  azoxy-benzene  with  iron  filings.    3.  By  the  oxidation 

of  hydrazo-benzene.    4.  By  the  oxidation  of  amino-compounds, 

e.g.  together  with  azoxy-compounds  by  means  of  KMnO4: 

2C6H6.NH2  +  20 


5.  By  the  action  of  nitroso-  upon  amino-compounds  in  pre- 
sence of  acetic  acid.  In  this  way  azo-benzene  is  obtained  from 
nitroso-benzene  and  aniline  acetate  : 

C6H5.NO  +  NH2.C6H5  =  C6H5.N:N-C6H5  +  H20. 

Ammo-  and  hydroxy-derivatives  of  azo-benzenes  are  known, 
thus  :  — 

C6H6.N:N.C6H4.NH2  C6H6.N:N.C6H4.QH 

Amino-azo-benzene  Hydroxy-azo-benzene. 

The  former  are  at  the  same  time  bases  and  azo-compounds, 
and  the  latter  azo-compounds  and  phenols  (i.e.  weak  acids). 
(Cf.  Azo-dyes,  p.  399.) 

/2-Phenyl-hydroxylamine,  C6H5.NH-OH,  is  formed  when 
nitro-benzene  is  reduced  with  zinc  dust  and  water,  more 
especially  in  the  presence  of  a  mineral  salt,  e.g.  CaCl2.  It  is 
a  colourless  crystalline  substance  melting  at  81°,  and  is 
relaf'  ly^unstable.  Aqueous  solutions  rapidly  undergo  oxi- 
dation on  exposure  to  the  air,  yielding  azoxy-benzene;  oxidiz- 
ing agents  generally  yield  nitroso-benzene.  Mineral  acids 
immediately  cause  molecular  rearrangement  into  p-amino- 
phenol,  NH2-C6H4.OH  (cf.  p.  394).  All  the  arylated  /3-hy- 
droxylamines  corresponding  with  phenyl-hydroxylamine  reduce 
Fehling's  solution,  and  this  affords  a  test  for  an  aromatic  nitro- 
compound.  If,  after  warming  with  water  and  zinc  dust,  a  solu- 
tion is  obtained  which  reduces  FeMing's  solution,  the  presence 
of  a  nitro-group  in  the  original  compound  can  be  inferred. 

D.  Hydrazines 

The  aromatic  hydrazines  (E.  Fischer)  entirely  correspond 
with  those  of  the  fatty  series  (cf.  p.  111). 

Phenyl-hydrazine,  CGH5  •  NH  •  NH2,  s-diphenyl-hydrazine  or 
hydrazo-benzene,  C6H6  •  NH  •  NH  •  CeH6;  unsym.-diphenyl- 


398  XXII.   DIAZO-  AND  AZO-COMPOUNDS 

hydrazine,     (C6H5)2N  •  NEL    and    phenylmethyl  -  hydrazine, 
(C6H5)(CH3)N.NH2,  are  all  known. 

Phenyl-hydrazine,  C6H5«NH»NH2,  forms  a  colourless  crys- 
talline mass,  melting  at  23°  to  a  colourless  oil,  which  quickly 
becomes  brown  from  oxidation,  and  which  is  best  distilled 
under  reduced  pressure.  When  kept  or  when  heated  it  under- 
goes slow  decomposition  (Chattaway).  It  forms  salts  with 
mineral  acids,  e.g.  the  hydrochloride,  C6H5N2H3,  HC1  (plates). 
Like  all  hydrazines,  it  has  strong  reducing  power,  reducing 
Fehling's  solution  even  in  the  cold.  It  is  readily  destroyed  by 
oxidation  (Chattaway,  C.  N.  1911,  103,  217),  but  is  stable  to- 
wards mild  reducing  agents.  Energetic  reducing  agents  con- 
vert it  into  aniline  and  ammonia.  Gentle  oxidation  of  the 
sulphate  by  means  of  HgO  converts  it  into  benzene-diazonium 
sulphate.  It  is  prepared:  (a)  by  reducing  benzene-diazonium 
chloride  with  the  calculated  quantity  of  SnCl2  and  HC1: 

C6H6N2C1  +  4H  =  C6H6.NH.NH2,HC1; 


(b)  by  reducing  potassium  diazo-  benzene  -sulphonate,  C6H5- 
NrN-SOgK  (from  06H5N2C1  and  K2SO?),  with  zinc  dust  and 
icetic  acid  to  potassium  phenyl-hydrazine-sulphonate,  CGH5« 
NH»NH»S03K,  which  is  then  hydrolysed  to  phenyl-hydrazine 
and  sulphuric  acid  : 

CcH5.NH-NH.S08K  +  HC1  +  H20  =  CeHj-NH-NHa,  HC1  +  KHS04. 

Alkyl  and  acyl  derivatives  of  phenyl-hydrazine  are  known; 
the  former  (mono-alky  lated  derivatives  only)  are  obtained  by 
the  action  of  alkyl  iodides  on  the  base  or  its  metallic  deriva- 
tives. Phenyl-methyl-hydrazine,  which  can  be  obtained  in 
this  way,  is  largely  used  for  differentiating  ketoses  and  aldoses 
(p.  302);  its  constitution  follows  from  its  formation  by  the 

/~1    TT 

reduction  of  nitroso-methyl-aniline,  Q|J  6^>N«NO.    Both  mono- 

and  diacyl  derivatives  are  known.  The  mono-acyl  derivatives 
or  hydrazides  (cf.  Amides,  Anilides)  are  obtained  by  the 
action  of  the  acid  or  acid  anhydrides  on  the  base;  they  give 
a  violet-red  coloration  with  sulphuric  acid  and  dichromate  of 
potash,  and  can  be  used  for  isolating  acids  which  are  readily 
soluble  (B.  22,  2728),  e.g.  acetylphenyl-hydrazide,  C6H5-NH. 
NH.CO-CH8;  m.-pt.  128°. 

The  base  is  an  important  and  often  an  exceedingly  delicate 
reagent  for  aldehydes  and  ketones,  combining  with  them  to 
hydrazones,  with  elimination  of  water  (cf.  pp.  127  and  135). 


AZO-DYE8  399 

Most  of  these  compounds  are  solid  and  crystalline,  and  are 
therefore  eminently  suited  for  the  recognition  of  aldehydes 
and  ketones.  With  certain  sugars  it  yields  phenyl-hydrazones, 
but  with  an  excess  of  the  base,  osazones  (p.  301)  are  formed. 
Diketones,  keto-aldehydes,  &c.,  also  yield  osazones. 

With  ethyl  aceto- acetate,  phenyl-hydrazine  forms  pyrazole 
derivatives,  &#.  phenyl-methyl-pyrazolone,  the  methyl  deriva- 
tive*of  whrch  is  antipyrine  (see  p.  230). 

Drphenyl-hydrazine,  (CgH5)2N»NH2,  is  an  oily  base  which 
boils  without  decomposition,  and,  like  phenyl-hydrazine,  is 
easily  oxidized;  it  only  reduces  Fehling's  solution,  however, 
when  warmed.  It  is  obtained  by  reducing  diphenyl-nitros- 
amine,  (C6H5)2N-NO,  with  zinc  dust  and  acetic  acid.  M.-pt. 
34°.  Like  phenyl-hydrazine,  it  yields  characteristic  hydra- 
zones  and  osazones  with  the  sugars. 

^-Bromo-phenyl-hydrazone,  C6H4Br*NH«NH2,  and|?-nitro- 
phenyl-hydrazine  are  often  used  in  isolating  ketones,  &c.,  as 
the  phenyl-hydrazones  thus  obtained  crystallize  well  (B.  1899, 
32,  1806). 

E.  Azo-dyes 

A  number  of  compounds  derived  from  azo-benzene  and  its 
homologues  are  largely  used  as  dyes,  under  the  name  of  azo- 
dyes.  These  compounds  are  either  basic  and  contain  NH2  or 
N(CH3)2  groups,  or  are  acidic  and  then  contain  either  phenolic, 
OH,  or  sulphonic,  S02  •  OH,  and  phenolic  groups.  Azo-benzene 
itself  is  a  highly-coloured  substance,  but  is  not  a  dye.  In 
order  that  a  coloured  substance  shall  be  a  dye,  it  is  essential 
that  the  colour  it  imparts  to  a  fabric  shall  not  be  removed  by 
washing  or  treatment  with  soap.  According  to  0.  Witi>  when 
certain  characteristic  groups  known  as  chromophores,  among 
which  are  «N:N  and  N02,  are  present,  the  compound  is 
coloured  or  is  a  chromogene ;  and  when,  in  addition  to  the 
chromophore,  a  strongly  basic  (e.g.  NH2)  or  acidic  group  (e.g. 
•  OH  or  •  S02  •  OH)  is  also  present,  we  obtain  a  dye,  e.g. : 

Chromogeues.  Dyes. 

Nitre-benzene  Nitraniline,  N02<C6H4-NH2; 

Nitro-benzene  Picric  acid,  (NO2)3.C6H2.OH; 

^.zo-benzene  £>-Hydroxy-azo-benzene,  C6H6-N:N-C6H4'OH. 

The  majority  of  dyes,  when  reduced,  yield  colourless  com- 
pounds— leuco-compounds — which  on  oxidation  are  converted 
into  the  original  dyes. 

With  regard  to  the  theory  of  the  process  of  dyeing  fabrics, 


400  XXII.   DIAZO-  AND   AZO-COMPOUNDS 

there  are  still  two  distinct  schools.  According  to  one,  the  process 
consists  in  the  formation  of  definite  compounds  of  the  basic  or 
acidic  dye  with  acidic  or  basic  constituents  of  the  fabric  dyed. 
According  to  the  other,  the  operation  is  largely  a  physical  one, 
and  the  dyed  fabric  may  be  regarded  as  a  solid  solution. 

In  most  cases,  silk  and  woollen  —  and  in  a  few  cases  cotton  — 
fabrics  can  be  dyed  by  direct  immersion  in  a  solution  of  the 
dye;  but,  as  a  jule,  cotton  will  not  dye  directly,  but  recmires 
previous  treatment  with  a  mordant.  The  object  of  fehPmor- 
dant  is  to  deposit  some  substance  on  the  fabric  which  will 
afterwards  combine  with  or  fix  the  dye.  The  chief  mordants 
employed  for  acid  dyes  are  the  feeble  bases  aluminic,  chromic, 
or  ferric  hydroxides,  obtained  by  immersing  the  fabric  in  a 
solution  of  the  metallic  acetate,  and  then  subjecting  to  the 
action  of  steam.  The  product  formed  by  the  action  of  the 
dye  on  the  mordant  is  known  as  a  lake,  and  the  same  dye  can 
give  rise  to  different-coloured  lakes,  according  to  the  mordant 
used.  When  basic  dyes  are  employed  for  cotton  goods,  the 
fabric  is  usually  mordanted  with  tannic  acid.  Stannic  hy- 
droxide obtained  from  such  a  salt  as  SnCl4,  2NH4C1  is  also 
used  as  a  mordant. 

^-Amino-azo-benzene  is  the  parent  substance  of  the  dyes 
known  as  chrysoidines.  It  may  be  obtained  (1)  by  nitrating 
azo-benzene  and  then  reducing  (this  indicates  its  constitution 
as  an  amino-derivative  of  azo-benzene);  (2)  by  molecular  re- 
arrangement of  diazo-amino-benzene  (p.  393): 


;    gives    NH2.C6H4.N:N.C6H5, 


another  example  of  the  wandering  of  a  radical  from  a  side 
chain  into  the  benzene  nucleus.  The  amino-group  occupies 
the  ^-position  with  respect  to  the  azo-group. 

Substituted  amino-azo-benzenes,  e.g.  dimethyl-amino-azo- 
benzene,  are  obtained  directly  by  the  action  of  a  diazonium 
salt  on  a  tertiary  amine: 

=  C6H5.N:N.C6H4.N(CH3)2  +  HC1. 


Assuming  the  Blomstrand  formula  for  the  diazonium  sait, 
the  reaction  is  probably  first  additive,  and  then  HC1  is 
eliminated  : 


CHRYSOIDINES  AND  TROP^OLINES  401 

The  azo-group  always  takes  up  the  ^-position  with  respect 
to  the  substituted  amino-group  if  this  position  is  free.  If, 
however,  the  jo-position  is  already  substituted,  a  dye  is  not 
formed,  or  is  formed  very  incompletely,  and  the  o-position  is 
taken  up. 

The  chrysoidines  are  coloured  yellow  to  brown,  and,  as  they 
contain  amino-  or  substituted  amino-groups  in  the  molecule, 
are  basic,  and  form  well-defined  salts  with  mineral  acids. 

Among  the  simplest  chrysoidines  we  have : — 

Aniline  yellow,  the  hydrochloride  of  j;-amino-azo-benzene. 
It  is  now  very  little  used. 

Chrysoidine,  or  2-A-diamino-azobenzene  hydrochloride,  CrH5« 
N :  N .  C6H3(NH2)2,  HC1  [N2 :  (NH2)2  =  1:2:4].  It  dyes  silk  and 
wool  directly  an  orange-red  colour. 

Bismarck  brown,  or  3':Z'A-triamino-azo-benzene  hydrochloride, 
NH2.C6H4.N:N.C6H3(NH2)2,HC1,  is  obtained  by  diazotizing 
w-phenylenediamine  and  coupling  the  diazonium  salt  with  a 
second  molecule  of  the  base. 

The  brown  coloration  obtained  by  the  addition  of  a  few 
drops  of  dilute  nitrous  acid  solution  to  m-phenylenediamine 
is  due  to  the  formation  of  Bismarck  brown  or  a  related  sub- 
stance. The  hydrochloride  crystallizes  in  reddish  -  brown 
plates. 

Many  of  the  chrysoidine  dyes  are  sulphonated  derivatives 
of  amino-azo-benzene.  As  an  example,  we  have  methyl  orange, 
which  is  the  sodium  salt  of  helianthine  or  jp-dimethamino-azo- 
benzene-^-sulphonic  acid,  (CH3)2N.C6H4.N:N.C6H4.S02.OH. 
It  is  largely  made  use  of  as  an  indicator  in  volumetric  analysis, 
as  it  is  not  affected  by  weak  acids,  e.g.  carbonic,  but  is  an  ex- 
tremely delicate  reagent  for  the  feeblest  alkalis. 

The  dyes  known  as  tropaeolines  are  derivatives  of  ^-hydroxy- 
azo-benzene.  Such  compounds  are  obtained  by  adding  the  cold 
diazotized  solution  to  an  alkaline  solution  of  a  phenol.  The 
dye  is  then  salted  out  by  the  addition  of  sodium  chloride  and 
collected.  The  reaction  is  often  made  use  of  in  testing  for  a 
primary  aromatic  amine  (p.  389),  as  the  precipitates  produced 
are  usually  coloured  bright  red.  The  azo-group  invariably 
occupies  the  p-position  with  respect  to  the  OH  group,  unless 
this  is  already  substituted. 

^-Hydroxy-azo-benzene  crystallizes  in  brick-red  prisms,  and 
is  a  yellowish-red  dye. 

Resorcin  yellow,  OH.S02.C6H4.N:N;C6H3(OH)2,  2A-di- 
hydroxy-azo -benzene- 4' '-sulphonic  acid,  obtained  by  coupling  a 

(B480)  2C 


402  XXII.   DIAZO-  AND  AZO-COMPOUNDS 

diazotized  solution  of  sulphanilic  acid  with  an  alkaline  solu- 
tion of  resorcinol,  is  known  as  Tropseolin  0. 

The  constitution  of  an  azo-dye  can  usually  be  determined  by 
an  examination  of  its  decomposition  products,  especially  the 
products  formed  by  energetic  reduction ;  e.g.  Bismarck  brown, 
on  reduction  with  tin  and  hydrochloric  acid,  yields  a  mixture 
of  1 : 3-diamino-  and  1:2: 4-triamino-benzene : 

NH2  :        NH, 

<(      \N:|N 
N /  2H;2I_ 

Bis-azo-dyes. — Certain  well-known  dyes,  e.g.  Biebrich  scarlet, 
contain  two  azo-groups.  Such  can  be  obtained  by  diazotizing 
an  amino-derivative  of  azo-benzene,  and  then  coupling  it  with 
a  tertiary  amine  or  with  a  phenol,  and  we  thus  obtain  com- 
pounds of  the  type  CgH5.N:N.C6H4.N:N.C6H4.OH. 

Another  type  of  bis-azo-compound  is  formed  by  coupling  a 
diamine  or  dihydric  phenol  with  2  mols.  of  a  diazonium  salt. 

Many  amino-  and  hydroxy-azo-derivatives  react  as  tauto- 
meric  substances,  especially  those  which  contain  an  NH2  01 
OH  group  in  the  ortho  -  position  with  respect  to  the  N2 
radical.  These  react  as  though  they  were  quinone  hydra- 
zones  or  quinone-imide  derivatives,  e.g.: 

C6H5.N:N.C6H4.OH     —  C6H6NH.N:C6H4:O, 
C6H6.N:N.C6H4.NH2  —  C6H6.NH.N:C6H4:NH. 

For  a  general  summary  compare  Auwers  (A.  1908,  360,  11). 
The  general  conclusion  drawn  is  that  all  the  compounds,  both 
para  and  ortho,  are  true  hydroxy-azo-compounds. 

According  to  Hantzsch,  many  of  the  hydroxy-azo-compounds 
are  pseudo-acids  (p.  363),  i.e.  the  hydrogen  compound  is  the 
quinone  hydrazone;  but  in  the  formation  of  a  salt,  intra- 
molecular rearrangement  occurs,  and  the  salt  thus  has  a  con- 
stitution quite  different  from  that  of  the  parent  substance,  e.g.: 

C6H5.NH.N:C6H4:0  - 


F.  Phosphorus  Compounds,  &c.;  Org-ano-Metallie 
Derivatives 

The  phosphorus,  &c.,  compounds  of  the  fatty  series  have 
their  analogues  in  corresponding  compounds  of  the  aromatic; 
these  latter  have  been  investigated  by  Michaelis  and  his 
pupils  (A.  181,  188,  201,  212,  and  229 ;  B.  28,  2205):  for 


SULPHONIC  ACIDS  403 

instance,  phenyl  phosphine,  CGHr.PH2;  phenyl  phosphinic 
acid,  C6H5PO(OH)2;  phosphenyl  chloride,  CtfH5-PCl2;  phos- 
phino-benzene,  C6H5P02;  and  phospho -benzene,  C6H5P:P« 
C6H5  (these  two  last  being  analogous  to  nitro-  and  to  azo- 
benzene).  Some  of  those  compounds  are  solid,  and  they  are 
less  volatile  and  more  stable  than  the  corresponding  aliphatic 
compounds.  Corresponding  derivatives  of  arsenic  are  also 
known. 

Aromatic  Organo  -  Metallic  Compounds.  —  Mercury,  tin, 
lead,  tellurium,  and  magnesium  yield  phenyl  derivatives. 
Mercury  phenyl,  Hg(C6H5)2,  is  obtained  by  the  action  of 
sodium  amalgam  of  bromobenzene.  It  is  relatively  stable. 
Numerous  compounds  of  the  type  of  phenyl  magnesium 
bromide,  C6H5-Mg-Br,  have  been  prepared,  and  are  used  as 
synthetical  reagents  (cf.  p.  356). 


XXIII.  ABOMATIC  SULPHONIC  ACIDS 

The  aromatic  sulphonic  acids  are  very  similar  in  properties 
to  the  sulphonic  acids  of  the  fatty  series,  but  can  be  obtained 
much  mofe  readily.  One  of  the  characteristic  properties  of 
benzene  and  its  derivatives  is  the  readiness  with  which  they 
react  with  concentrated  sulphuric  acid,  yielding  sulphonic 
acids.  In  some  cases  fuming  sulphuric  acid  is  used;  in  others 
sulphuryl  chloride,  OH-SO^Cl. 

Benzene-sulphonic  acid,  C6H5.S02»OH  (Mitscherlich,  1834), 
is  formed  when  benzene  is  heated  with  concentrated  sulphuric 
acid  for  some  hours : 

C6H6  +  S02(OH)2  =  C6H5.S02.OH  +  H20. 

As  in  the  case  of  ethyl  hydrogen  sulphate,  advantage  is 
taken  of  the  solubility  of  its  barium,  calcium,  or  lead  salt  to 
separate  it  from  the  excess  of  sulphuric  acid;  or  its  sodium 
salt  is  separated  by  the  addition  of  sodium  chloride. 

It  crystallizes  in  small  plates  containing  1JH20,  deliquesces 
in  the  air,  and  is  readily  soluble  in  alcohol.  The  barium  salt 
crystallizes  in  glistening  mother-of-pearl  plates  containing  1H2O. 

It  is  very  stable,  and  is  not  hydrolysed  when  boiled  with 
alkalis  or  acids  (cf.  Ethyl  hydrogen  sulphate).  It  is,  however, 


404  XXIII.   AROMATIC  SULPHONIC  ACIDS 

decomposed  into  benzene  and  sulphuric  acid  when  heated  with 
hydrochloric  acid  at  150°,  or  with  water  vapour  at  a  high 
temperature  (cf.  p.  347): 


C6H5.S02.OH  +  H20  =  C6H6  +  S02(OH)2. 


When  fused  with  alkali,  it  yields  phenol  in  the  form  of  its 
potassium  salt: 

C6H5.S03K  +  2KOH  =-  C6Hfi.OK  +  S03K2  +  H20, 

and  when  distilled  with  potassium  cyanide,  it  yields  benzo- 
nitrile: 

C6H6.SO3K  +  CNK  =  C6H6.CN  +  S03K2. 

With  PC15  the  OH  group  present  in  the  sulphonic  acid 
radical  is  replaced  by  chlorine,  and  benzene-sulphonic  chloride 
is  formed: 

C6H6.S02OH-f  PC16  =  C6H5-S02C1-|-POC13  +  HC1. 

This  is  an  oil,  insoluble  in  water;  it  melts  at  14-5°,  and  boils 
at  120°  (under  10  mm.  pressure);  as  an  acid  chloride  it  is 
reconverted  into  sulphonic  acid  by  hot  water,  into  the  corre- 
sponding esters  by  alcohols,  and  into  benzene-sulphonamide, 
C6EL«S02«NH2  (lustrous  mother-of-pearl  plates  melting  at 
150°),  by  ammonia.  This  compound  can  be  sublimed,  and 
corresponds  with  other  amides  in  its  properties.  The  amido- 
group,  however,  is  so  affected  by  the  strongly  acidifying  action 
of  the  S02  group  that  its  hydrogen  is  replaceable  by  metals, 
and  the  sulphonamides  consequently  dissolve  in  aqueous  solutions 
of  alkali  hydroxides. 

The  sulphonamides  are  largely  made  use  of  in  distinguish- 
ing the  various  sulphonic  acids.  These  acids  themselves  are 
difficult  to  purify,  as  a  rule  do  not  crystallize  well,  and  have 
no  definite  melting-point.  The  sulphonamides,  on  the  other 
hand,  crystallize  readily,  and  have  sharp  melting-points.  The 
sodium  salt  of  the  acid  is  treated  with  PC15,  and  the  chloride 
thus  obtained  is  warmed  with  ammonium  carbonate. 

Benzene-sulphonic  chloride  likewise  yields  sulphonamides 
with  primary  and  secondary  amines,  C6H5'S02«NHR  and 
C6H5'S02»NRB/,  the  former  of  these  being  soluble  in  alkali, 
but  the  latter  insoluble.  Tertiary  amines  do  not,  of  course, 
give  sulphonamides.  This  serves  as  the  basis  of  a  method  for 
separating  primary,  secondary,  and  tertiary  bases,  especially 


AMINO-SULPHONIC  ACIDS  405 

when  /3-anthraquinone  sulphonic  chloride  is  used  (Hinsberg, 
B.  23,  2962;  1900,  33,  477,  557,  3526;  38,  906). 

When  benzene-sulphonic  chloride  is  treated  with  zinc  dust, 
zinc  benzenesulphinate  is  formed  : 


2C6H6.S02Cl  +  2Zn  =  (C6H6S02)2Zn  +  ZnCl2. 

An  alkaline  sulphinate  is  also  produced  (along  with  phenyl 
disulphide  as  by-product)  when  benzene-sulphonic  chloride  is 
treated  with  thio-phenol  in  presence  of  alkali. 

Benzene-sulphuric  acid  crystallizes  in  large  glistening  prisms, 
readily  soluble  in  hot  water,  alcohol,  and  ether.  It  possesses 
reducing  properties,  and  is  itself  converted  into  thio-phenol  by 
nascent  hydrogen: 

C6H6.S02H  +  4H  =  C6H6SH  -f  2H20. 


Substitution  may  be  effected  in  benzene-sulphonic  aoid  by 
chlorine,  bromine,  and  the  groups  N02  and  NH2. 

The  nitro-benzene-sulphonic  acids,  N02»C6H4»S03H,  are 
obtained  by  nitrating  benzene-sulphonic  acid  or  by  sulphonat- 
ing  nitro-benzene,  the  w-compound  preponderating.  Reduc- 
ing agents  convert  them  into  the  — 

Amino-  benzene  -sulphonic  acids,  NH2'C6H4«S03H.  The 
^-compound,  which  is  termed  sulphanilic  acid,  is  obtained  by 
heating  aniline  sulphate  at  180°-200°  (Gerhardt,  1845);  also  by 
reducing  ^-nitro-benzene-sulphonic  acid.  The  conversion  of 
aniline  sulphate  into  sulphanilic  acid  proceeds  in  the  following 
stages  :  — 

NH3HSO4         NH.SO2-OH 


Aniline  hydrogen    Phenylsulphonamto 
sulphate  acid 


SO2'OH  Aniline 

Sulphanilic  acid      o-siilphonic  acid. 

(Of.  Eamberger,  B.  1897,  30,  2274.)     It  crystallizes  in  rhombic 
plates  (+  H2O),  sparingly  soluble  in  water,  forms  metallic  salts, 


406  XXIII.    AROMATIC  SULPHONIC  ACIDS 

e.g.  sodium  sulphanilate,  NH2  •  C6H4  •  S08Na  +  2H20  (large 
plates),  but  does  not  combine  with  acids.  The  formula 

C6H4<^qQ  3/>   possibly  expresses   the  constitution  of   sulph- 

anilic  acid.  The  m-acid,  also  termed  metanilic  acid,  is  em- 
ployed in  the  preparation  of  azo-dyes,  e.g.  metaniline  yellow; 
it  crystallizes  in  fine  needles  or  prisms. 

Diazo-benzene-sulphonic  acid,  C6H4<^gQ  ^>  (the  anhydride 
of  C6H4<^Q  TT  Y  is  obtained  by  adding  a  mixture  of  sul- 

phanilate  and  nitrite  of  sodium  to  dilute  sulphuric  acid.  It 
forms  colourless  needles,  sparingly  soluble  in  water,  shows  all 
the  reactions  of  the  diazo-compounds,  and  is  of  great  impor- 
tance for  the  preparation  of  azo-dyes. 

Benzene-disulphonic  acids,  C6H4(S03H)2  (principally  meta-), 
and  benzene-trisulphonic  acids,  C6H3(S03H)3,  result  from  the 
energetic  sulphonation  of  benzene  with  fuming  sulphuric  acid. 
The  former  exist,  of  course,  in  three  isomeric  modifications. 
"When  they  are  distilled  with  KCN,  they  yield  the  compounds 
C6H4(CN)2,  the  nitriles  of  the  phthalic  acids;  when  fused  with 
KOH,  the  m-disulphonic  acid  changes  into  resorcinol  (m-di- 
hydroxy-benzene),  G6H4(OH)2. 

Almost  all  the  homologues  of  benzene,  with  the  exception 
of  hexamethyl-benzene,  yield  sulphonic  acids.  From  toluene 
are  obtained  the  o-,  m-,  and  ^-toluene  sulphonic  acids,  CH3- 
C6H4.S03H  (Hollemann  and  Caland,  B.  1911,  44,  2504).  Of 
these  it  is  the  p-acid  which  is  formed  in  largest  quantity 
directly;  its  potassium  salt  crystallizes  beautifully. 

The  sulphonic  acids  of  the  three  xylenes,  the  xylene-sul- 
phonic  acids,  C6H3(CH3\2S03H,  serve  for  the  separation  of 
these  isomers  from  each  other;  and  the  power  of  crystalliza- 
tion of  the  salts  or  amides  of  the  sulphonic  acids  of  the  higher 
benzene  homologues  is  frequently  made  use  of  for  the  recog- 
nition and  separation  of  these  hydrocarbons. 

The  above  instances  are  sufficient  to  show  that  sulphonic 
acids  may  be  obtained  from  the  most  complicated  aromatic 
compounds.  This  is  of  especial  importance  if  the  latter  are 
dyes  whose  application  is  hindered  by  their  insolubility  in 
water,  as  in  the  case,  e.g.,  of  indigo,  amino-azo-benzene,  &c. 
The  sulphonated  dyes,  however,  are  usually  inferior  to  their 
originals  in  colouring  power  arid  purity,  e.g.,  they  do  not  stand 
the  effects  of  light  so  well. 


XXIV.   PHENOLS  407 

XXIV.  PHENOLS 

The  hydroxylic  derivatives  of  benzene  and  its  homologues 
are  usually  divided  into  (a)  phenols  and  (b)  aromatic  alco- 
hols. The  phenols  all  contain  the  hydroxyl  group  or  groups 
directly  attached  to  the  benzene  nucleus,  e.g.  C6H5(OH), 
C6H4(OH)2,  whereas  in  the  alcohols  the  hydroxyl  group  is 
present  in  a  side  chain,  e.g.  C6H5«CH2-OH. 

One  important  point  of  difference  between  the  phenols  and 
alcohols  is  the  more  pronouncedly  acidic  nature  of  the  phenol. 
The  aromatic  alcohols  closely  resemble  those  of  the  aliphatic 
series,  but  the  phenols  react  as  feeble  acids,  the  hydroxylic 
hydrogen  being  displaced  by  the  action  of  sodium  or  potassium 
hydroxide. 

The  phenols  are  either  liquid  or  solid  compounds,  and  are 
often  characterized  by  a  peculiar  odour,  e.g.  carbolic  acid  and 
thymol.  Most  of  them  can  be  distilled  without  decomposition, 
and  all  are  readily  soluble  in  alcohol  or  ether;  some  dissolve 
easily  in  water,  others  less  readily,  the  solubility  tending  to 
increase  with  the  number  of  hydroxyl  groups  present  in  the 
molecule.  Many  of  them  are  antiseptics,  e.g.  phenol,  creosol, 
and  resorcinol.  . 

The  phenols  are  usually  divided  into  mono-,  di-,  tri-  or  tetra- 
hydric,  according  to  the  number  of  OH  groups  present  in  the 
molecule. 

Behaviour. — 1.  Like  the  alcohols,  the  phenols  are  capable 
of  forming  ethers  such  as  anisole,  C6H5«0-CH3,  esters,  e.g. 
phenyl  acetate,  C6H5  •  0  •  CO  •  CH3,  and  phenyl  hydrogen 
sulphate,  C6H60  •  S02  •  OH,  thio-coinpounds,  e.g.  thiophenol, 
C6H5.SH,  &c. 

They  can  only  be  compared  with  the  tertiary  alcohols,  since 
they  cannot,  like  the  primary  or  secondary  alcohols,  yield  acids 
or  ketones  containing  an  equal  number  of  carbon  atoms  in  the 
molecule  upon  oxidation. 

2.  The  phenols  are  weak  acids,  and  form  salts  known  as 
phenates  or  phenoxides,  e.g.  C6H5«OK,  potassium  phenate  or 
potassium  phenoxide;  most  of  the  salts  are  readily  soluble  in 
water,  and  far  more  stable  than  the  alcoholates,  with  which 
they  correspond. 

In  aqueous  solutions  the  salts  are  largely  hydrolysed,  and 
are  decomposed  by  carbon  dioxide,  as  the  phenols  are  ex- 
tremely feeble  acids  comparable  with  hydrocyanic  acid  (cf. 
Walker,  Phys.  Chem.,  chapter  xxiv).  The  acid  character  of  the 


408 


XXIV.  PHENOLS 


J^O) 

CD  Ci 

66 


o    o    o    o    o 
CO  (N  Oi  ^  l>- 
i—  i  CM  O  CO  CO 
CM  (N  <?q  CM  <M 


o  I-H 


o  2 

cq  o  cq 
co  -^    I 

CM 


W 


S   1 


REACTIONS  OF  PHENOLS  409 

phenols  is  considerably  increased  by  the  entrance  of  negative 
groups,  especially  N02,  into  the  molecule.  (See  Picric  acid; 
also  Abst.  1903,  1,  754.) 

3.  The  presence  of  NH2  or  OH  groups  in  the  benzene 
nucleus  renders  compounds  much  more  reactive  towards  halo- 
gens, nitric  acid,  sulphuric  acid,  oxidizing  agents,  &c.  With 
polyamines  and  aminophenols  the  reactivity  is  such  that  the 
compounds  undergo  spontaneous  oxidation  on  exposure  to  the 
air.  The  reactivity  with  chlorine  is  so  great  that  frequently 
compounds  of  this  type  cannot  be  chlorinated  by  the  usual 
methods.  Orton  and  King  (J.  C.  S.  1911,  1185)  have  introduced 
a  method  based  upon  the  fact  that  the  reversible  reaction: 

K-NClAc  +  HCl  ^  B-NHAc 


proceeds  from  left  to  right  in  the  presence  of  glacial  acetic 
acid,  and  thus  by  taking  very  dilute  solutions  of  hydrochloric 
acid,  e.g.  0*021  N,  the  concentration  of  the  chlorine  is  kept  so 
low  that  chloro-derivatives  are  obtained  free  from  products  of 
oxidation.  Cresols  can  be  chlorinated  in  the  same  manner. 
The  acetyl  derivative  generally  used  is  2  :  4-dichloro-acetyl- 
chloranilide,  and  if  the  theoretical  amount  of  this  compound  is 
used  the  reaction  proceeds  to  completion,  as  hydrogen  chloride 
is  formed  by  the  action  of  the  chlorine  on  the  amine  or  phenol. 

4.  Many  phenols  give  characteristic  colorations  with  ferric 
chloride  in  neutral  solution,  e.g.  phenol  and  resorcinol  violet, 
catechol  green,  and  orcinol  blue-violet;  while  pyrogallol  yields 
a  blue  colour  with  ferrous  sulphate  containing  a  ferric  salt, 
and  a  red  one  with  ferric  chloride.     Bleaching-powder  and 
iodine  solution,  in  certain  cases,  also  give  particular  coloration. 

5.  Liebermann's  Reaction.  —  When   the   phenols  are  mixed 
with  concentrated  H2S04  and  a  drop  of  nitrite  solution  or  of 
a  nitrosamine,  they  yield  intensely  coloured  solutions  which 
turn   to  a  deep-blue  or  green  when   diluted   and   rendered 
alkaline  with  potash. 

6.  The  sodium  and  potassium  salts  of  the  phenols  react 
with  C02  (Kolbe)  or  with  COC12,  with  formation  of  aromatic 
hydroxy-acids,  e.g.  salicylic  acid  (see  this). 

For  further  methods  of  preparation  of  hydroxy-acids  and 
aldehydes,  see  Tiemann-Reimer  reaction  (pp.  430  and  440). 

7.  The  phenols  couple  with  diazonium  salts  to  form  azo- 
dyes  (p.  389);  when  heated  with  benzo-trichloride,  CgHyCC^, 
they  yield  yellow-red  dyes  (see  Aurin),  and  with  phthalic  acid, 
the  phthaleins  (see  Phenol-phthalein). 


410  XXIV.   PHENOLS 

8.  When  heated  with  zinc  dust,  the  phenols  are  converted 
into  the  corresponding  hydrocarbons  (Baeyer). 

9.  When  heated  with  the  additive  compounds  of  zinc  chloride 
and  ammonia  or  calcic  chloride  and  ammonia,  the  OH  is  replaced 
by  NH2  (cf.  p.  368;  also  B.  19,  2901). 

10.  Heating  with  phosphorus  pentachloride  partially  con- 
verts the  phenols  into  chlorinated  hydrocarbons,  and  heating 
with  P2S5  into  thio-phenols. 

Occurrence.  —  Many  individual  phenols  are  found  in  the 
vegetable  and  animal  kingdoms,  and  also  in  coal-tar. 

Constitution.  —  The  hydroxyl-groups  in  phenol,  C6H5  •  OH,  and 
in  the  di-  and  polyhydroxy-benzenes,  containing  six  carbon 
atoms,  are  linked  to  the  benzene  nucleus.  That  this  is  also 
the  case  in  the  homologues  of  these  compounds  follows: 
(a)  from  their  completely  analogous  reactions;  (b)  from  their 
behaviour  upon  oxidation.  Thus,  when  oxidized,  w-cresol 
yields  m-hydroxy-benzoic  acid,  and  hence  the  OH  is  present 
in  the  benzene  nucleus  and  not  in  the  side  chain,  and  must 
be  in  the  m-position  with  respect  to  the  methyl  group. 

A.  Monohydrie  Phenols 

Modes  of  Formation.  —  1.  Many  phenols  are  formed  during 
the  destructive  distillation  of  the  more  complex  carbon  com- 
pounds, especially  of  wood  and  coal;  they  are  therefore 
present  in  wood-  and  coal-tars.  The  latter  contains  more 
especially  phenol  and  its  homologues,  cresol,  &c.;  the  former, 
among  other  products,  the  methyl  ethers  of  polyhydric  phenols, 
e.g.  guaiacol,  C6H4»(OH)(0»CH3),  and  its  homologue  creosol, 
C6H3(CH3)(OH)(O.CH3). 

The  phenols  are  isolated  from  coal-tar,  &c.,  by  shaking  with 
sodic  hydroxide  solution,  in  which  they  dissolve,  saturating 
the  alkaline  solution  with  hydrochloric  acid,  and  purifying  the 
precipitated  phenols  by  fractional  distillation. 

2.  Phenols  are  formed  together  with  an  alkali  sulphite  when 
salts  of  sulphonic  acids  are  fused  with  potassic  or  sodic  hy- 
droxides (KekuU,  Wurtz,  Dusart,  1867): 


C6H6.S03K  +  2KOH  =  C6H6.QK  +  SO3K2  +  H2O. 

In  the  laboratory  nickel  or  silver  basins  are  used  for  this 
fusion,  and  on  the  large  scale  iron  boilers,  £c.  The  alkali 
salts  of  the  phenols  are  formed,  and  the  free  phenols  may  be 
liberated,  by  the  addition  of  mineral  acid.  The  chlorinated 


PREPARATION  OF  PHENOLS  411 

sulphonic  acids  and  the  chlorinated  phenols  also  exchange  the 
halogen  for  hydroxyl  when  fused  with  potash: 

C6H4C1(SO3K)  -f  4KOH  =  C6H4(OK)2  +  SO3K2  -f  KC1  +  2H20. 

In  certain  cases  intramolecular  rearrangement  occurs  during 
this  fusion,  e.g.  all  three  bromo-benzene-sulphonic  acids,  the 
ortho-,  meta-,  and  para-,  yield  m-dihydroxy-benzene  (resorcinol) 
when  fused  with  potash. 

3.  They  are  formed  when  aqueous  solutions  of  diazonium 
salts  are  heated  (Griess-,  cf.  p.  387).     As  a  rule,  a  very  dilute 
sulphuric  acid  solution  is  employed: 

C6H4C1(N2C1) -f- H2O  =  CcH4Cl-OH  +  N2-f  HC1. 

4.  Phenol  is  produced  from  benzene  by  the  action  of  ozone 
or  hydrogen  peroxide,  and  also  by  that  of  the  oxygen  of  the 
air  in   presence   of   caustic   soda   solution   or   of   aluminium 
chloride.     In  an  analogous  manner  di-  and  even  trihydroxy- 
benzene  may  be  obtained  by  fusing  phenol  with  potash : 

CCH6.OH  +  0  =  C6H4(OH)2. 

5.  The  phenols  cannot  be  prepared  from  chloro-,  bromo-,  or 
iodo-benzene   in  the  same  way  as    the  alcohols  from  alkyl 
chlorides,  bromides,  or  iodides,  the  halogen  being  bound  too 
firmly  to  the  benzene  nucleus.     If,  however,  nitro-groups  are 
present  in  o-  or  ^-positions,  an  exchange  of  this  kind  can  be 
effected  by  heating  with  aqueous  sodium  or  potassium  hy- 
droxides;   trinitro-chloro-benzene    indeed    reacts   with   water 
alone : 

CCH2C1(N02)3  +  HOH  =  C6H2(OH)(N02)3  +  HC1. 

Similarly,  the  amino-group  in  amino-compounds  may  be 
replaced  by  hydroxyl  by  means  of  boiling  alkalis,  provided 
nitro-groups  are  also  present  in  certain  position;  thus  o-  and 
p-  (not  m-)  dinitro-aniline  yield  dinitro-phenols,  a  reaction 
which  corresponds  with  the  saponification  of  the  amides  (cf. 
pp.  362  and  374). 

6.  Phenols   are   also   formed  when   salts   of   the  aromatic 
hydroxy-acids  are  distilled  with  lime,  or  when  their  silver 
salts  are  carefully  heated: 

CCH2(OH)3.C02H  =  C02-hCGH3(OH)3 

Gallic  acid  Pyrogallol. 

Phenol,    Carbolic  acid,   hydroxy -benzene,   C6H5OH,  was   dis- 


412  XXIV.   PHENOLS 

covered  in  1834  by  Runge  in  coal-tar.  It  occurs  in  the  urine 
of  the  herbivora  and  in  human  urine  as  phenyl  hydrogen  sul- 
phate, also  in  castoreum,  and  in  bone-oil.  It  forms  a  colourless 
crystalline  mass  consisting  of  long  needles,  melts  at  42°,  boils 
at  181°,  is  soluble  in  fifteen  parts  of  water  at  16°,  and  itself 
dissolves  some  water,  a  small  percentage  of  the  latter  sufficing 
to  liquefy  the  crystalline  phenol.  Alcohol  and  ether  dissolve  it 
readily.  It  is  hygroscopic,  and  acquires  a  reddish  colour  in  the 
air  owing  to  the  presence  of  impurities,  possesses  a  character- 
istic odour  and  burning  taste,  is  poisonous,  acts  as  a  splendid 
antiseptic,  and  exerts  a  strongly  corrosive  action  upon  the  skin. 
As  a  very  feeble  acid  it  dissolves  readily  in  caustic  potash 
solution,  but  not  in  the  carbonate.  Ferric  chloride  colours  the 
aqueous  solution  violet,  while  a  pine  shaving  moistened  with 
hydrochloric  acid  is  turned  greenish-blue  by  phenol. 

Hexahydro-phenol,  06HU  •  OH,  prepared  from  quinitol  (cyclo- 
hexane-1  :  4-diol)  (B.  26,  229),  is  a  liquid  with  an  odour  resem- 
bling that  of  fusel  oil. 

Anisole,  or  Phenyl  methyl  ether,  C6H5  •  0  •  CHg,  and  phenetole, 
or  phenyl  ethyl  ether,  C6H5  •  0  •  C2H6,  are  best  obtained  by  heat- 
ing phenol  and  caustic  potash  with  methyl  or  ethyl  iodide  in 
alcoholic  solution  : 

C6H5.OK  +  CH3I  =  C6H5.OCH3-}-KIj 

the  former  is  also  obtained  by  distilling  anisic  acid  with  lime. 
They  are  liquids  of  ethereal  odour  which  boil  at  a  lower 
temperature  than  phenol,  just  as  ether  has  a  lower  boiling- 
point  than  alcohol.  They  are  very  stable  neutral  compounds, 
which  are  not  readily  hydrolysed  by  acids  or  alkalis;  when 
heated  with  HI  to  140°,  or  with  HC1  to  a  higher  temperature, 
or  with  aluminium  chloride,  they  are  decomposed,  yielding 
phenol  : 


Phenyl  ether,  Diphenyl  oxide,  (C6H5)20,  is  formed  when 
phenol  is  heated  with  ZnCl2  or  AlClg,  but  not  with  H2S04. 
It  crystallizes  in  needles,  and  is  not  decomposed  by  hydriodic 
acid. 

Esters.—  Phenyl  hydrogen  sulphate,  C6H.  •  0  •  S02  •  OH  (cf. 
Ethyl  hydrogen  sulphate),  is  only  capable  of  existence  in  the 
form  of  salts,  being  immediately  hydrolysed  into  phenol  and 
sulphuric  acid  when  attempts  are  made  to  isolate  it.  The 
potassium  salt,  C6H60«S02.OK  (plates,  sparingly  soluble  in 


THIO-PHENOL  413 

water),  is  found  in  the  urine  of  the  herbivora  and  also  in 
human  urine  after  the  consumption  of  phenol,  and  it  may 
be  prepared  synthetically  by  heating  potassium  phenate  with 
potassic  pyro-sulphate  in  aqueous  solution  (Baumann).  It  is 
very  stable  towards  alkalis,  but  is  saponified  by  hydrochloric 
acid. 

Phenyl  acetate,  C,HLO  •  CO  •  CH3,  obtained  from  phenol, 
acetic  anhydride,  and  dry  sodic  acetate,  is  a  liquid  which 
boils  at  193°,  and  is  readily  hydrolysed  (cf.  Ethyl  acetate). 

Thio-phenol,  Phenyl  hydrosulphide,  C6H5«SH,  is  prepared 
from  benzene-sulphonic  chloride,  C6H5'S02C1,  as  given  at 
p.  405,  or  by  heating  phenol  with  P2S5.  It  is  a  liquid  of 
most  unpleasant  odour  and  of  pronounced  mercaptan  char- 
acter (see  p.  89).  It  yields,  for  instance,  a  mercury  com- 
pound, (C6H6S)2Hg,  crystallizing  in  glistening  needles,  and 
also  salts  with  other  metals.  When  warmed  with  concen- 
trated H2S04,  a  cherry-red  and  then  a  blue  coloration  is 
produced. 

Closely  related  to  the  above  are:  (a)  phenyl  sulphide,  (C6H5)2S, 
which  is  formed  by  the  action  of  benzene-diazonium  chloride 
upon  thio-phenol  (B.  23,  2469): 


It  is  a  liquid  smelling  of  leeks,  and  is  oxidizable  to  phenyl 
sulphone,  (C6H5)2S02;  (b)  phenyl  disulphide,  (C6H5)2S2  (glisten- 
ing needles,  m.-pt.  60°),  which  is  very  easily  prepared  by  the 
action  of  iodine  upon  the  potassium  compound  of  thio-phenol, 
or  by  exposing  an  ammoniacal  solution  of  the  latter  to  the  air. 
It  is  readily  reduced  to  thio-phenol,  and  may  be  indirectly 
oxidized  to  benzene-disulphoxide,  (C6H5)2S202.  (Cf.  the  cor- 
responding compounds  of  the  fatty  series,  p.  89,  et  seq.) 

SUBSTITUTED  PHENOLS 

Chloro-  and  Bromo-phenols.  —  When  chlorine  is  led  into 
phenol,  o-  and  j?-chloro-phenols  are  formed.  These,  and  also 
the  m-compound,  may  be  obtained  by  reducing  and  diazotizing 
the  haloid  nitro-benzenes. 

Of  the  isomeric  di-derivatives,  the  ^-compounds  have  the 
highest  melting-point  and  the  o-  the  lowest;  thus  0-chloro-  and 
bromo-phenols  are  liquid  and  the  ^-compounds  solid.  When 
fused  with  caustic  potash  they  yield  dihydroxy  -  benzenes 
(p.  411),  often  with  a  molecular  rearrangement.  The  chloro- 


414  XXIV.   PHENOLS 

phenols  have  a  sharp,  persistent  odour.  All  the  5  hydrogen 
atoms  of  phenol  can  be  replaced  by  chlorine  and  bromine. 

When  an  excess  of  bromine  water  is  added  to  an  aqueous 
solution  ©f  phenol,  a  precipitate  of  s-tribromo-phenol  (colour- 
less needles,  melting  at  92°)  is  obtained. 

Nitroso-phenol,  OH'C6H4»NO,  prepared  from  phenol  and 
nitrous  acid  (Baeyer,  B.  7,  964),  by  boiling  nitroso-dimethyl- 
aniline  with  caustic -soda  solution  (see  p.  378),  and  by  the 
action  of  hydroxylamine  upon  quinone,  is  identical  with  qui- 
none  monoxime,  0:C6H4:N«OH  (p.  430).  It  crystallizes  in 
fine  colourless  needles  which  readily  become  brown,  or  in  large 
greenish-brown  plates,  and  detonates  when  heated. 

Nitro-phenols. — A  mixture  of  o-  and  p-nitio -phenols  is  ob- 
tained when  phenol  is  mixed  with  cold  dilute  nitric  acid;  the 
^-compound  preponderates  if  the  liquid  is  cold,  and  the  ortho- 
if  it  is  warm.  When  distilled  with  steam,  the  1:2  compound 
volatilizes,  while  the  1:4  remains  behind.  m-Nitro-phenol  is 
obtained  by  diazotizing  w-nitraniline. 

The  o-  and  jp-compounds  can  also  be  obtained  by  fusing  o- 
and  ^-nitranilines  with  potash,  and  ^-nitro-phenol  has  been 
synthesised  from  nitro-malonaldehyde,  NO2  •  CH(CHO)2,  and 
acetone  (Hill  and  Torray,  B.  1895,  28,  2598). 

The  o-compound  crystallizes  in  yellow  prisms,  and  melts  at 
45°,  the  m-  in  yellow  crystals,  melting  at  96°,  and  the  para-  in 
colourless  needles,  melting  at  114°. 

The  acid  character  of  phenol  is  so  strengthened  by  the 
entrance  of  the  nitro-group  that  its  salts  are  not  decomposed 
by  carbonic  acid,  but  are  formed  from  the  nitro-phenols  and 
alkali  carbonate.  Sodium  o-nitro-phenate,  C6H4(N02)ONa, 
crystallizes  in  dark -red  prisms,  and  potassium  jo-nitro-phenate 
in  golden  needles.  (For  constitution  of  the  salts,  see  chapter 
on  Absorption  Spectra.)  Halogens  and  nitric  acid  readily 
substitute  further  in  these  mono-nitro-compounds ;  nitric  acid 
yields  two  isomeric  dinitro-phenols,  C6H3(N02)2OH,  (OH: 
NO2:N02  =  1:2:4  and  1:2:6,  i.e.  tt-e  two  N02  groups  are 
always  in  the  m-position  to  one  another).  Further  nitration 
in  the  presence  of  sulphuric  acid  gives — 

Picric  acid,  s-Trinitro-phenol,  C6H2(N02)3.OH,  (OH:N02: 
N02:N02  =  1:2:4:6).  This  compound  was  discovered  in 
1799.  It  may  also  be  prepared  by  the  direct  oxidation  of 
s-trinitro-benzene  with  K3FeC6Ng,  and  is  produced  by  the 
action  of  concentrated  nitric  acid  upon  the  most  varied  or- 
ganic substances,  e.g.  silk,  leather,  wool,  resins,  and  aniline. 


AMINO-PHENOLS  415 

It  is  a  strong  acid  and  forms  beautifully  crystalline  salts,  which 
explode  violently  when  heated  or  struck.  It  crystallizes  from 
alcohol  or  water  in  yellow  plates  or  prisms,  melting  at  122°,  is 
only  sparingly  soluble  in  water,  and  the  aqueous  solutions  have 
a  persistent  deep-yellow  colour.  It  is  used  for  the  preparation 
of  explosives,  and  is  also  a  yellow  dye. 

Picryl  chloride,  CLH?(N02)3C1  (from  picric  acid  and  PC15), 
resembles  the  acid  chlorides  (p.  362)  in  behaviour.  Picric  acid 
forms  beautifully  crystallizing  additive  compounds  with  many 
aromatic  hydrocarbons,  and  also  with  amines  and  phenols. 

Ammo-phenols  are  obtained  by  the  reduction  of  nitro- 
phenols : 

C6H4(OH)NH2  C6Hs(OH)(NH2)a   C6H3(OH)(N02)(NH2)   C6H2(OH)(NHa)8 

0-,  m-,  p-  Diamino-  Nitro-amino-  Triamino- 

Amino-phenols  phenols  phenols  pheuoL 

In  the  amino-phenols  (Hofmann,  1857)  the  acid  character  of 
the  phenols  is  neutralized  by  the  presence  of  the  amino-group, 
so  that  they  only  yield  salts  with  acids.  The  amino-phenols 
themselves  are  relatively  unstable,  and  readily  decompose  on 
exposure  to  moist  air  or  sunlight,  but  the  hydrochlorides  are 
much  more  stable.  Derivatives  of  these  compounds,  as  phenols 
and  as  amines,  are  known.  The  amino-hydrogen  is  readily 
replaceable  by  acyl  groups. 

^-Ammo-phenol,  m.-pt.  184°,  obtained  by  the  electrolysis  of 
nitrobenzene  in  concentrated  sulphuric  acid  (Gattermann),  or 
by  molecular  rearrangement  from  /3-phenyl-hydroxylamine, 
is  easily  oxidized  to  quinone,  C6H402,  and  is  converted  by 
bleaching-powder  into  quinone  chlor-imide,  O:C6H4:NC1.  It 
is  used  as  a  photographic  developer  under  the  name  of  rodinal. 
Amidol  is  a  salt  of  2:4-diamino-phenol. 

m-Amino-phenol  and  diethyl-m- ammo-phenol,  C6H4(OH) 
[N(C2H§)2],  are  formed  when  m-amino-benzene-sulphonic  acid 
or  its  diethyl-derivative  is  fused  with  alkali. 

The  anisidines,  amino-anisoles,  methoxy-anilines,  CH30«C6H4« 
NH2,  and  the  phenetidines,  C2H5O.C6H4-NH2,  are  bases 
similar  to  aniline,  and  are  used  in  the  colour  industry  (azo- 
dyes).  The  acetyl  derivative,  aceto-p-phenetidine,  C2H50« 
C6H4»NH'CO'CH3,  which  forms  colourless  crystals,  is  used 
as  an  anti-pyretic  and  as  a  remedy  for  neuralgia  under  the 
name  of  "Phenacetine".  Phenocoll  is  lactyl-phenetidine. 

Numerous  complex  sulphur  compounds  derived  from  amino- 
phenols  are  used  as  dyes  (e.g.  Primulines,  Vidal-black,  &c.). 


416  XXIV.    PHENOLS 

Phenol-sulphonic  acids,  OH- C6H4-S(V OH.— The  o-  and 
|?-acids  are  obtained  from  phenol  and  concentrated  H0S04  at 
a  moderate  temperature,  that  is,  with  much  greater  ease  than 
the  benzene-sulphonic  acids;  the  ortho-acid  changes  into  the 
para-  when  its  aqueous  solution  is  heated.  The  two  acids 
may  be  separated  by  means  of  their  potassium  salts.  The 
m-compound  can  be  prepared  indirectly  by  fusing  m-benzene- 
disulphonic  acid  with  potash.  All  three  are  crystalline. 

The  o-  and  m-acids  yield  o-  and  wi-dihydroxy-benzenes  when 
fused  with  KOH,  but  the  ^?-acid  does  not  react  in  this  way, 
being  attacked  only  at  temperatures  over  320°,  when  complex 
products  are  formed.  0-Phenol-sulphonic  acid  is  used  as  an 
antiseptic  under  the  name  of  "Aseptol"  or  "Sozolic  acid";  simi- 
larly, the  salts  of  di-iodo-^-phenol-sulphonic  acid,  OH«C6H2I2- 
S03H,  "Sozo-iodol",  form  antiseptics  resembling  iodoform. 

HOMOLOGUES  OF  PHENOL 

The  homologues  of  phenol  resemble  the  latter  very  closely 
in  most  of  their  properties,  form  perfectly  analogous  deriva- 
tives, possess  disinfecting  properties,  and  also  a  peculiar  odour 
(the  cresols  an  unpleasant  faecal-like,  and  the  higher  homo- 
logues only  a  faint  odour). 

They  differ  from  phenol  mainly  by  the  presence  of  side 
chains  which,  as  in  the  case  of  toluene,  &c.,  may  undergo 
certain  transformations.  Especially  when  they  are  used  in 
the  form  of  alkyl  or  acyl  derivatives  or  acid  sulphates,  they 
can  be  oxidized  in  such  a  manner  that  the  side  chains  (methyl 
groups)  are  transformed  into  carboxyl,  with  the  production  of 
hydroxy-carboxylic  acids.  The  cresols  themselves  cannot  be 
oxidized  in  this  way  even  by  chromic  acid  mixture,  and  are 
completely  destroyed  by  potassic  permanganate.  Negative 
substituents,  especially  if  they  are  present  in  the  0-position, 
render  such  oxidation  more  difficult  in  acid,  but  facilitate  it 
in  alkaline  solution. 

All  three  cresols,  CH3«C6H4«OH,  are  present  in  coal-tar, 
and  are  also  contained  in  the  tar  from  pine  and  beech  wood; 
they  are  most  readily  prepared  from  the  corresponding 
toluidines.  0-Cresyl  hydrogen  sulphate  (analogous  to  phenyl 
hydrogen  sulphate)  is  found  in  the  urine  of  horses,  and  the 
^-compound  in  human  urine. 

m-Cresol  is  conveniently  prepared  by  heating  thymol  with 
phosphoric  anhydride  and  then  with  potash. 


DIHYDRIO  PHENOLS  417 

^-Cresol  is  produced  during  the  putrefaction  of  albumen. 
Its  dinitro-compound  is  a  golden-yellow  dye  which  is  used  as 
ammonium  or  potassium  salt  under  the  name  of  Victoria 
orange. 

Crude  cresol  is  rendered  soluble  in  water  by  the  addition 
of  resin  soap  or  of  oil  soap;  the  preparations  so  obtained  are 
termed  creoline  and  lysol,  and  are  employed  as  antiseptics. 

Thymol,  C^H^O,  I -methyl- 4: -isopropyl- 3 -hydroxy -benzene,  is 
found  together  with  cymene,  C10H14,  and  thymene,  010Hj6,  in 
oil  of  thyme,  Thymus  Serpyllum,  and  is  used  as  an  antiseptic. 

The  isomeric  carvacrol,  l-methyl-^-isopropyl-Z-hydroxy-benzene, 
present  in  Origanum  hirtum,  is  prepared  either  by  heating 
camphor  with  iodine  or  from  its  isomer,  carvol,  and  glacial 
phosphoric  acid. 

The  constitutions  of  these  two  phenols  have  been  established 
as  follows :  (a)  Both  yield  cymene  (^-methyl-isopropyl-benzene) 
when  heated  with  phosphorus  sulphide  and  similar  compounds. 
(b)  Carvacrol,  when  heated  with  phosphorus  pentoxide,  yields 
propylene  and  o-cresol.  (c)  Thymol,  when  similarly  treated, 
yields  propylene  and  m-cresol. 

C3H7.C6H3(CH3)(OH)  =  C3Hfl  +  OH.C6H4.CH3(oorm). 

B.  Dihydrie  Phenols 

By  the  entrance  of  two  hydroxyls  into  benzene  and  its 
homologues,  the  dihydric  phenols  are  produced.  These  are 
analogous  to  the  monohydric  compounds  in  most  of  their 
relations,  but  differ  from  them  in  the  same  way  as  the 
dihydric  alcohols  from  the  monohydric.  The  methods  of 
formation  are  analogous  to  those  used  for  the  monohydric 
phenols,  especially  by  fusion  of  sulphonic  acids  and  halogen 
derivatives  with  potash;  instead,  however,  of  the  compound 
expected,  an  isomeride  which  is  stable  at  that  high  tempera- 
ture frequently  results  (see  Resorcinol).  The  j?-dihydroxy- 
compounds  are  characterized  by  their  close  connection  with 
the  quinones.  Many  of  the  polyhydric  phenols  are  strong 
reducing  agents. 

Catechol,  formerly  called  pyrocatechin,  C6H4(OH)2  (1:2), 
which  was  first  obtained  by  the  distillation  of  catechin 
(Mimosa  Catechu),  is  present  in  raw  beet-sugar,  and  is  ob- 
tained when  many  resins  or  0-phenol-sulphonic  acid  are  fused 
with  potash.  It  crystallizes  in  short,  white,  rhombic  prisms, 

(B480)  2D 


418  XXIV.   PHENOLS 

which  can  be  sublimed,  and  dissolves  readily  in  water,  alcohol, 
and  ether. 

It  is  usually  prepared  by  heating  its  mono-methyl  ether, 
guaiacol,  C6H4(OH)(OCH3),  a  constituent  of  beech-wood  tar, 
with  hydriodic  acid  (see  Anisole,  p.  410).  Like  most  of  the 
polyhydric  phenols,  it  is  very  unstable  in  alkaline  solution, 
which  quickly  becomes  green  and  then  black  in  the  air.  The 
aqueous  solution  is  coloured  green  by  ferric  chloride,  and 
then  violet  by  ammonia  (reactions  of  the  o-dihydroxy-com- 
pounds).  It  possesses  reducing  properties,  and  precipitates 
silver  even  from  a  cold  solution  of  silver  nitrate.  By  the  con- 
tinued action  of  chlorine  upon  it,  derivatives  of  pentamethy- 
lene  and  finally  of  the  fatty  series  result  (Zincke  and  Kuster). 
By  boiling  it  with  potash  and  potassic  methyl-sulphate,  it  may 
be  reconverted  into  guaiacol,  which  likewise  shows  the  ferric 
chloride  reaction  and  possesses  reducing  powers. 

Resorcinol,  or  m-Dihydroxy-benzene  (Hlasiwetz,  Barth,  1864), 
is  obtained  when  many  resins  (Galbanum,  Asafcetida),  m-phenol- 
sulphonic  acid,  all  three  bromo-benzene-sulphonic  acids,  or  m- 
and  j?-benzene-disulphonic  acids  are  fused  with  potash.  The  last- 
mentioned  compounds  are  employed  for  its  preparation  on  the 
technical  scale.  It  crystallizes  in  rhombic  prisms  or  plates, 
which  quickly  become  brown  in  the  air,  dissolves  readily  in 
water,  alcohol,  and  ether,  and  reduces  an  aqueous  solution  of 
silver  nitrate  when  warmed  with  it,  and  an  alkaline  solution 
even  in  the  cold.  With  ferric  chloride  it  gives  a  dark-violet 
coloration.  It  acts  therapeutically  like  carbolic  acid,  only 
more  mildly. 

When  heated  with  phthalic  anhydride,  it  is  converted  into 
fluorescein  (p.  493);.  test  for  m-dihydroxy-benzenes),  and  it  is 
therefore  manufactured  on  the  large  scale.  Nitrous  acid  or  dia- 
zonium  compounds  transform  it  into  azo-dyes ;  with  the  latter 
it  can  yield  mono-azo-dyes  or  primary  Bis-azo-dyes  (cf.  p.  402). 
Its  trinitro-derivative  is  styphnic  acid,  C6H(OH)2(N02)3,  which 
is  formed  by  the  action  of  nitric  acid  upon  many  gum  resins. 

Quinol,  formerly  called  hydroquinone,  p-dihydroxy -benzene 
(Wohler,  1844),  may  be  obtained  by  the  oxidation  of  quinic 
acid,  C7H1206,  by  means  of  Pb02,  by  the  hydrolysis  of  the 
glucoside  arbutin,  and  from  succinylo-succinic  ester  (cf.  p. 
241),  &c.  It  is  usually  prepared  by  the  reduction  of  quinone 
with  sulphurous  acid,  and  hence  the  name  hydroquinone. 
It  crystallizes  in  monoclinic  plates  or  hexagonal  prisms, 
of  about  the  same  solubility  as  its  isomers,  and  may  be 


TRIHYDRIC   PHENOLS  419 

sublimed.  Ammonia  colours  it  reddish-brown,  while  chromic 
acid,  ferric  chloride,  and  other  oxidizing  agents  convert  it  into 
quinone  or  quinhydrone  (p.  431).  It  melts  at  169°,  and,  being  a 
strong  reducing  agent,  it  is  used  as  a  developer  in  photography. 

Lead  acetate  solution  yields  a  white  precipitate  with  a 
solution  of  catechol,  but  none  with  resorcinol,  while  quinol  is 
only  precipitated  in  presence  of  ammonia.  From  the  observed 
heats  of  neutralization,  resorcinol  and  quinol  behave  towards 
soda  as  dibasic  acids,  and  catechol  as  a  weak  monobasic  acid. 

Orcinol,  or  m-Dihydrwy-toluene,  (CH3:OH:OH  =  1:3:5),  is 
found  in  many  lichens  (Rocella  tindoria,  Lecanora,  &c.).  It  is 
formed  by  the  elimination  of  carbon  dioxide  from  or-sellinic 
acid,  e.g.  upon  fusing  extract  of  aloes  with  potash,  and  it  can 
also  be  prepared  synthetically  from  toluene  (B.  15,  2992).  Of 
especial  interest  is  its  synthesis  from  ethyl  acetone-dicarboxylate 
(p.  260)  and  sodium  (B.  19,  1446).  It  does  not  yield  a  fluor- 
escein  with  phthalic  anhydride. 

Homo-catechol,  C6H3(CH3)(OH)2,  (CH3:OH:OH  =  1:3:4), 
deserves  mention  on  account  of  its  mono-methyl  ether  creosol, 
CH3  -  C6H3(OH)(0  •  CH3),  occurring  in  beech-wood  tar.  Creosol 
is  a  liquid  similar  to  guaiacol,  boiling  at  220°,  and,  as  a  deri- 
vative of  catechol,  gives  a  green  coloration  with  ferric  chloride. 

Quinitol  (Cydohexane  -1:4-  diol),  p-dihydroxy  -  hexamethylene, 
C6H10(OH)2,  a  dihydroxy -derivative  of  reduced  benzene,  is  ob- 
tained synthetically  by  the  reduction  of  p-diketo-hexamethylene. 
It  crystallizes  in  crusts,  and  has  a  sweet  taste  with  a  bitter 
after-taste;  m.-pt.  144°.  It  is  the  simplest  representative  of 
the  inosite  sugar  group  (p.  421). 

C.  Trihydric  Phenols 

Pyrogallol,  Pyrogallic  add  (Sclieele,  1786),  l:2:3-trihydroxy- 
benzene,  is  the  most  important  of  these  three  isomers..  It  is 
obtained,  apart  from  synthetical  reactions,  by  heating  gallic 
acid,  when  carbon  dioxide  is  eliminated: 

C6H2(OH)3.C02H  =  C6H3(OH)3  +  C02. 

It  crystallizes  in  white  plates,  melts  at  132°,  is  readily 
soluble  in  water,  and  capable  of  subliming  without  decom- 
position. It  is  an  energetic  reducing  agent,  e.g.  for  silver 
salts,  and  is  used  as  a  developer  in  photography.  Its  alkaline 
solution  rapidly  absorbs  oxygen,  hence  its  use  in  gas  analysis. 


420  XXIV.   PHENOLS 

The  aqueous  solution  is  coloured  bluish-black  by  a  solution 
of  ferrous  sulphate  containing  ferric  salt,  and  purple-red  by 
iodine.  It  does  not  react  with  hydroxylamine  (cf.  Phloro- 
glucinol). 

Pyrogallol  dimethyl  ether,  C6HS(OE)(OCHS)2  (Hofmann), 
is  contained  in  beech-wood  tar,  as  are  likewise  the  dimethyl 
ethers  of  the  compounds  C6H2(CH3)(OH)3  and  C6H2(C3H7) 
(OH)3,  homologous  with  pyrogallol. 

Phloroglucinol,  or  l:3:5-Trihydroxy-benzene  (Hlasiwetz,  1855), 
is  obtained  by  the  fusion  of  various  resins  and  of  resorciriol 
with  potash  or  soda,  by  the  action  of  alkali  upon  the  gluco- 
side  phloretin,  and  by  fusing  its  dicarboxylic  ester  (whose 
synthetical  formation  is  given  on  p.  439)  with  potash.  It 
forms  large  prisms  which  weather  in  the  air,  melts  at  218°, 
and  sublimes  without  decomposition.  With  ferric  chloride  it 
gives  a  dark-violet  coloration,  its  solutions  in  alkalis  readily 
absorb  carbon  dioxide,  and  it  possesses  reducing  properties. 

Phloroglucinol  is  a  typical  example  of  a  tautomeric  com- 
pound. 

In  many  reactions,  e.g.  (a)  the  formation  of  metallic  deriva- 
tives, C6H3(OK)3;  of  a  trimethyl  ether,  C9H8(OCH8),  which  is 
insoluble  in  alkali;  and  of  a  triacetyl  derivative,  C6H3(OAc)3; 
(b)  its  combination  with  phenyl-carbimide  to  form  a  tricarbani- 
line  derivative,  C6H3(0«CO»NH«C6H5)3,  it  reacts  as  a  normal 
phenol,  i.e.  as  sym.  trihydroxy-benzene.  On  the  other  hand, 
however,  in  certain  of  its  reactions  it  behaves  as  a  ketone,  i.e. 

as  triketo-hexamethylene,  CO<^Qjj2'<QQ^>CH2;  thus  it  yields 

a  trioxime,  C6H6(  :  N  •  OH)3,  and  when  alkylated  in  presence  of 
alcoholic  potash  yields  tetra-  and  hexa-alkyl  derivatives,  e.g. 

*  Its  ultra-violet  absorption 


rtrum  (Hedley,  J.  C.  S.  1906,  730)  resembles  that  of  other 
lols. 

Hydroxy-quinol,  1:2  -A-  Trihydroxy-benzene,  is  obtained  by 
fusing  quinol  with  potash.  Like  pyrogallol,  it  yields  no 
oxime  with  hydroxylamine. 

Hexahydroxy-benzene,  Cg(OH)6,  forms  as  its  potassium 
salt  potassium  carboxide,  C606K6,  the  explosive  compound 
sometimes  obtained  in  the  manufacture  of  metallic  potassium. 
It  crystallizes  in  colourless  prisms,  has  no  definite  melting- 
point,  but  decomposes  at  about  200°,  and  can  be  converted 
into  its  quinone. 


AROMATIC  ALCOHOLS  42 1 

ftuercitol,  CLH7(OH)5,  found  in  the  oak,  and  inosite  or 
iiiositol,  C6H6(OH)6,  found  in  the  muscles  of  the  heart,  are 
polyhydroxy-derivatives  of  hexamethylene.  In  many  respects 
they  closely  resemble  the  aliphatic  polyhydric  alcohols  rham- 
nitol  and  sorbitol.  Quercitol  melts  at  235°,  is  optically  active, 
and  has  [a]D  =  -j-24'16.  Inositol  or  hexahydroxy-cyclohexane 
exists  in  an  inactive  and  in  d-,  /-,  and  r-modifications. 


,  XXV.  AROMATIC  ALCOHOLS,   ALDEHYDES,   AND 
KETONES 

A.  Aromatic  Alcohols 

While  the  phenols  remind  us  of  the  tertiary  alcohols  of  the 
fatty  series,  although  they  differ  from  these  in  many  points, 
we  are  acquainted  with  compounds  which  possess  the  alcoholic 
character  in  its  entirety;  they  are  termed  aromatic  alcohols. 
The  most  important  of  these  is  (primary)  benzyl  alcohol, 
C7H7«OH,  which  is  isomeric  with  the  cresols,  this  isomerism 
being  explained  by  the  different  position  of  the  hydroxy-group 
in  the  molecule;  thus,  while  the  cresols,  like  all  phenols,  con- 
tain the  hydroxyl  linked  to  the  benzene  nucleus,  in  benzyl 
alcohol  it  is  present  in  the  side  chain: 

CH3  •  C6H4  •  OH  (cresols)        C6H6  •  CH2  •  OH  (benzyl  alcohol). 

*  This  follows  from  the  formation  of  benzyl  alcohol  from 
benzyl  chloride,  C6H5«CH2C1  (and  vice  versa),  and  also  from 
the  fact  that  it  can  be  oxidized  to  an  aldehyde  and  an  acid 
containing  the  same  number  of  carbon  atoms  in  the  molecule 
as  itself,  these  being  likewise  mono-derivatives  of  benzene : 

C6H6.CH2.OH  C6H5.CHO  C6H5.CO-OH 

Benzyl  alcohol  (Benzene-       Benzaldehyde  (Benzene-       Benzoic  acid  (Benzene- 
methylol)  methylal)  carboxylic  acid). 

Benzyl  alcohol  may  also  be  looked  upon  as  methyl  alcohol  in 
which  one  atom  of  hydrogen  is  replaced  by  the  group  C6H5: 

H  •  CH2  •  OH  (carbinol)        C6H6  •  CH2  •  OH  (phenyl-carbinol), 

and  is  therefore  the  simplest  aromatic  alcohol. 

In  addition  to  primary  alcohols,  e.g.  tolyl  alcohols,  CH»- 
C6H4.CH2OH,  ^-phenyl-ethyl  alcohol,  C6H6 •  CH2 . CH2OH, 


422          XXV.   AROMATIC  ALCOHOLS,   ALDEHYDES,   ETC. 

secondary,  e.g.  a-phenyl-ethyl  alcohol,  or  l-pkenyl-hydroxy* 
ethane,  C6H5  •  CH(OH)  •  CH3,  and  even  tertiary  alcohols,  e.g. 
(C6H5)3C»OH,  triphenyl-carbinol,  are  known.  Of  the  poly- 
hydric  alcohols,  phenyl-glycerol  (l-phenyl-l:2:3-trihydroxy- 
propane)  is  the  most  important.  All  of  these  contain  the 
hydroxyl  radicals  attached  to  carbon  atoms  of  the  side  chain 
and  not  to  those  of  the  nucleus,  and  this  is  the  fundamental 
difference  between  an  aromatic  alcohol  and  a  phenol.  The  alco- 
hols are  not  of  the  same  commercial  importance  as  the  phenols, 
and  hence  have  not  been  investigated  to  the  same  extent. 

All  these  compounds  are,  as  alcohols,  perfectly  analogous  to 
the  alcohols  of  the  fatty  series,  so  far  as  regards  the  formation 
of  alcoholates,  ethers,  esters,  mercaptans,  amines,  phosphines, 
&c.  They  are,  however,  at  the  same  time  benzene  derivatives, 
and  consequently  yield  chloro-,  bromo-,  nitro-,  amino-,  &c., 
substitution  products.  Unsaturated  aromatic  alcohols  are 
also  known,  which  resemble  the  unsaturated  compounds  of 
the  fatty  series  to  the  closest  extent  in  their  chemical  be- 
haviour, but  are  at  the  same  time  benzene  derivatives. 

These  remarks  also  apply  in  full  degree,  mutatis  mutandis,  to 
the  aromatic  aldehydes  and  ketones  (see  below). 

Benzyl  alcohol,  C6H5'CHo'OH,  is  a  colourless  liquid  of 
faint  aromatic  odour,  sparingly  soluble  in  water,  and  boils  at 
204:°.  It  occurs  naturally  in  Peru  and  Tolu  balsams  as  ben- 
zoic  and  cinnamic  esters,  and  is  formed  from  benzyl  chloride 
just  as  alcohol  is  from  ethyl  chloride.  It  is  usually  prepared 
by  the  action  of  concentrated  aqueous  potash  on  benzaldehyde, 
whereby  the  one  half  of  the  aldehyde  is  oxidized  and  the  re-« 
mainder  reduced  (B.  14,  2394): 

2C6H5.CHO  +  KOH  =  C6H5.CH2«OH  +  C6H6.COOK. 

Benzyl  alcohol  is  also  formed  when  benzamide  is  reduced 
with  sodium  amalgam.  This  is  a  reaction  which  has  been 
employed  for  the  preparation  of  a  number  of  substituted 
benzyl  alcohols  (Hutchinson,  B.  1891,  24,  173). 

Phenyl-methyl-carbinol,  C6H5 .  CH(OH) .  CH3,  b.-pt.  203°, 
can  be  prepared  by  reducing  acetophenone,  C6H5»CO-CH3 
(p.  427),  into  which  it  is  reconverted  by  gentle  oxidation. 

Numerous  secondary  and  tertiary  alcohols  have  been  synthe- 
sized within  recent  years  by  means  of  Grignard's  compounds 
(p.  356). 

The  simplest  of  the  unsaturated  alcohols  is  cinnamic  alco- 
hol, C6H6«CH:CH»CH2OH,  which  occurs  as  cinnamic  ester 


AROMATIC  ALDEHYDES  423 

("  styracin ")  in  storax.  It  crystallizes  in  glistening  needles 
of  hyacinth-like  odour,  yields  cinnamic  acid  when  gently  oxi- 
dized, and  benzoic  when  the  oxidation  is  more  vigorous. 

B.  Aromatic  Aldehydes 

Benzaldehyde,  Benzene-methylal,  or  oil  of  bitter  almonds, 
C6H5-CHO,  was  discovered  in  1803  and  investigated  by  Liebig 
and  W oliler  (A.  22,  1).  It  is  a  colourless,  strongly  refracting 
liquid  of  agreeable  bitter  almond-oil  odour.  It  boils  at  179°, 
has  a  sp.  gr.  1*05  at  15°,  and  is  readily  soluble  in  alcohol  and 
ether,  but  only  sparingly  in  water  (1  in  30). 

The  modes  of  formation  are  for  the  most  part  analogous  to 
those  described  under  the  aliphatic  aldehydes  (pp.  122  and 
123): 

(a)  By  the  oxidation  of  the  corresponding  alcohol.     This 
method,  although  of  considerable  practical  importance  in  the 
aliphatic  series,  is  of  but  theoretical  interest  in  the  aromatic, 
as   the  alcohols  themselves  are  usually  prepared  from  the 
aldehydes. 

(b)  By  the  distillation  of  the  calcium  salt  of  the  correspond- 
ing acid,  benzoic  acid,  with  calcium  formate. 

(c)  By  heating  the  corresponding  dichloride,  benzal  chloride, 
or   benzylidene   chloride,   C6H5-CHC12   (from   toluene),  with 
water  or  sulphuric  acid,  or,  as  is  done  on  the  technical  scale, 
with  water  and  lime;  also  by  heating  benzyl  chloride,  C6H5« 
CH2C1,  with  water  and  plumbous  or  cupric  nitrate. 

This  last  method  involves  a  process  of  hydrolysis : 

C6H5.CH2C1  —  C6H6.CH2.OH, 

and  also  a  process  of  oxidation: 

C6H5.CH2.OH  —  C6H6.C<^, 

both  of  which  are  brought  about  by  the  copper  nitrate  solu- 
tion. 

(d)  Together  with  dextrose  and  hydrocyanic  acid  by  decom- 
posing amygdalin,  C20H27OnN,  a  glucoside  (see  Glucosides) 
which  occurs  in  bitter  almonds  and  crystallizes  in  white  plates, 
either  by  means  of  sulphuric  acid  or  by  emulsin  (an  enzyme 
likewise  present  in  bitter  almonds,  cf.  pp.  267  and  592): 

C20H270UN  +  2H20  =  C6H5.CHO  +  2C6H12O6-f  CNH. 

(e)  By  the  action  of  chromyl  chloride,  Cr02Cl2,  upon  toluene, 


424          XXV.   AKOMAT1C  ALCOHOLS,   ALDEHYDES,   ETd. 

This  is  Etard's  reaction,  and  is  of  great  value  for  the  synthesis 
of  aldehydes  and  also  of  certain  ketones  from  hydrocarbons. 
An  additive  compound,  C6H5  •  CH3(Cr02Cl2)2,  is  first  formed, 
and  yields  the  aldehyde  on  the  addition  of  water  (B.  17,  1462, 
1700;  32,  1050. 

(/)  ^7  the  action  of  Grigiiard's  phenyl-magnesium  bromide 
on  ethyl  orthoformate  (Bodroux,  C.  E.  1904,  138,  92  and  700), 
e.g.: 

C6H6.Mg.Br-f-CH(OEt)3  =  Mg-Br-OEt  -f  C6H6-CH(OEt)2. 
C6H6-CH(OEt)2  hydrolysed  C6H6.CHO. 

Gattermann  and  Maffezzoli  (B.  1903,  36,  4152)  have  used  Gri- 
gnard's  compound  with  a  large  excess  of  ethyl  formate  at  low 
temperatures.* 

(g)  Homologues  of  benzaldehyde  are  sometimes  prepared 
by  the  elimination  of  carbon  dioxide  from  substituted  phenyl- 
glyoxylic  acids : 

C6H4X.CO-C02H  -*  C6H4X.C^Q, 

a  reaction  which  usually  takes  place  when  the  glyoxylic  acid 
is  distilled. 

Behaviour. — 1.  Its  behaviour  is  that  of  an  aldehyde,  and  in 
many  respects  it  closely  resembles  the  aliphatic  aldehydes.  Thus 
it  is  (a)  easily  oxidizable  to  the  acid,  and  on  this  account 
reduces  an  ammoniacal  silver  solution  with  the  production  of 
a  mirror;  (b)  reducible  to  the  alcohol;  (c)  capable  of  forming 
a  crystalline  additive  compound  with  NaHS03;  (d)  capable  of 
combining  with  HCN  (see  Mandelic  acid);  (e)  capable  of 
reacting  with  hydroxylamine  and  phenyl-hydrazine  to  benz- 
aldoxime,  GgHg-CHiN-OH,  and  benzaldehyde-phenyl-hydra- 
zone,  C6H5»CH:N2H'CgH5,  respectively;  (/)  converted  into 
benzylidene  chloride,  C6H6-CHC12,  by  the  action  of  phosphorus 
pentachloride. 

2.  Benzaldehyde  does  not  form  an  additive  compound  with 
ammonia  analogous  to  the  aldehyde-ammonias  of  the  aliphatic 
series,  but  enters  into  a  somewhat  complex  condensation,  the 
oxygen  of  the  aldehyde  being  eliminated  with  the  hydrogen 
atoms  of  ammonia  in  the  form  of  water,  the  complex  conden- 
sation product  hydrobenzamide  being  formed : 

3C6H6.CHO  +  2NH3  =  (C6H5.CH)3N2  +  3H2O. 

3.  Benzaldehyde   and   its   homoiogues   can   undergo   poly- 
*  For  synthetical  methods  see  Gattermann,  A.  1906,  347,  347. 


REACTIONS  OF  ALDEHYDES  425 

tnerization,  e.g.  when  an  alcoholic  solution  of  benzaldehyde  is 
boiled  with  potassium  cyanide,  benzoin  is  formed  : 

C6H6.CH:0  +  C6H5.CH:0  =  C6Hfi.CH(OH).CO.C6H6, 

a  compound  which  is  both  a  secondary  alcohol  and  a  ketone. 

4.  A  number  of  condensation  products  can  be  obtained 
from  the  aromatic  aldehydes,  and  many  of  these  are  of  com- 
mercial importance.  The  condensation  usually  takes  place 
in  the  presence  of  a  condensing  agent,  e.g.  acetic  anhydride, 
anhydrous  zinc  chloride,  potassic  hydroxide,  sodic  ethoxide, 
&c.  Among  some  of  the  simplest  of  these  condensations  are  :  — 

(a)  With  primary  amines.  The  formation  of  benzylidene 
anilines  (Schifs  Bases): 

=  H2O  +  C6H5.CH:N.C6H6. 


It  has  been  shown  recently  that  this  reaction  is  preceded  by 
the  formation  of  an  additive  compound,  C6H5«CH(OH)«NH« 
C6H5,  which  then  passes  into  the  benzylidene  derivative.  A 
few  such  additive  compounds  have  actually  been  isolated. 
(Dimroth  and  Zoepritz,  B.  1902,  35,  984.) 

(b)  With  tertiary  amines,  e.g.  : 

2C6H5.NMe2  +  C6H5.CHO  =  H2O  +  C6H6.CH(C6H4.NMe2)2, 

when  a  substituted  diamino-derivative  of  triphenyl-methane  is 
produced  (p.  483). 

(c)  With  the  sodium  salts  of  fatty  acids,  when  unsaturated 
acids  are  formed  (Perkin's  Synthesis,  pp.  441  and  442): 

C6H6  •  CHO  +  CH3  •  COONa  =  C6H6  .  CH  :  CH  •  C02Na  +  H20. 

(d)  With  fatty  aldehydes,  ketones,  &c.  : 

C6H6.CH:0  +  CHfc.CHiO  =  H2O  +  C6H5.CH:CH.CHO, 


when  unsaturated  aldehydes  (e.g.  cinnamic  aldehyde)  or  ketones 
are  formed. 

5.  Its  reaction  with  alkalis  (p.  422)  is  also  different;  in 
the  fatty  series  aldehyde  resins  are  formed,  and  with  benz- 
aldehyde  a  mixture  of  primary  alcohol  and  the  corresponding 
acid.     This  latter  reaction  is  characteristic  of  aldehydes  in 
which  the  CHO  group  is  directly  attached  to  the  benzene 
nucleus. 

6.  As  a  benzene  derivative,  it  can  be  substituted  by  halogens 
(indirectly),  and  can  be  nitrated,  sulphonated,  &c.  (directly). 


426          XXV.   AROMATIC  ALCOHOLS,   ALDEHYDES,   ETC. 

As  in  the  case  of  toluene,  chlorine  enters  the  side  chain  at 
the  boiling  temperature,  with  formation  of  benzoyl  chloride, 
OJL.COC1. 


Among  its  derivatives,  the  following  deserve  mention : — 

a-Benzaldoxime,  Benz-anti-aldoxime,  C6HB  •  CH :  N  •  OH,  is 
formed  from  benzaldehyde  and  hydroxylamine;  it  melts  at 
35°,  and  decomposes  when  boiled.  It  can  be  transformed  by 
means  of  acids  into  the  isomeric  /3-benzaldoxhne,  benz-syn- 
'aldoxime,  which  melts  at  125°  (for  velocity,  cf.  Patterson,  J. 
€.  S.  1907,  504;  1908,  1041),  and  in  contradistinction  to  the 
isomer,  readily  reacts  with  acetic  anhydride  yielding  benzo- 
nitrile.  The  oximes  are  stereo-isomeric  (Nitrogen-isomerism). 
(Cf.  pp.  138  and  428.) 

Benzaldehyde  -  phenyl  -  hydrazone,  C6H5  •  CH :  N  •  NHC6H5, 
forms  colourless  crystals,  melting  at  152°.  Benzylideneazine, 
CHPh :  N  •  N :  CHPh,  from  benzaldehyde  and  hydrazine  sul- 
phate, has  m.-pt.  93°. 

Nitro-benzaldehydes,  N02.C6H4.CHO.— The  m-compound 
is  the  chief  product  of  nitration,  but  some  20  per  cent  of  the 
o-compound  is  formed  at  the  same  time.  The  latter  is  best 
prepared  by  oxidizing  o-nitro-cinnamic  acid  by  KMn04  in  pre- 
sence of  benzene;  it  forms  long  colourless  needles,  melting  at 
46°,  yields  indigo  (p.  527)  with  acetone  and  caustic  soda,  and 
on  exposure  to  sunlight  forms  o-nitroso-benzoic  acid.  It  can 
be  reduced  to  o-amino-benzaldehyde,  NH2'CJE4»CHO,  a  com- 
pound crystallizing  in  silvery  glistening  plates,  m.-pt.  46°, 
which  is  of  value  for  various  synthetical  reactions.  (See 
Quinoline;  also  B.  16,  1833.)  m-Amino-benzaldehyde,  which 
is  prepared  from  w-nitro-benzaldehyde,  by  the  reduction  of  its 
bisulphite  compound,  is  used  in  the  production  of  triphenyl- 
methane  dyes. 

Cinnamic  aldehyde,  C6H5  •  CH :  CH  •  CHO,  is  the  chief  con- 
stituent of  oil  of  cinnamon  (Persea  cinnamomum),  from  which 
it  may  be  isolated  by  means  of  its  bisulphite-compound.  It  is 
an  oil  of  aromatic  odour,  boils  at  246°,  and  is  readily  volatile 
with  steam.  In  addition  to  its  properties  as  an  aldehyde,  it 
also  possesses  the  properties  of  an  unsaturated  compound,  e  g. 
forms  a  dibromide.  Its  reaction  with  potassium  hydrogen  sul- 
phite is  characteristic.  It  first  forms  an  additive  compound, 
O6H6GH:CH.CH(OH)(S03K),  like  an  ordinary  aldehyde,  and 
then,  as  an  unsaturated  compound,  combines  with  a  second 
molecule  of  the  sulphite,  yielding  C6H5  •  CH(S03K)  •  CH2  - 
€H(OH)(S03K)  +  2H20.  (B.  24,  1805;  31,  3301.) 


AROMATIC  KETONES  42? 

C.  Aromatic  Ketones 

The  aromatic  ketones  are  usually  divided  into  (1)  mixed 
aromatic  ketones,  viz.  those  which  contain  both  an  aryl  and 
an  alphyl  group,  e.g.  CgH5»CO'CH3,  and  (2)  true  aromatic  or 
diaryl  ketones,  e.g.  C6H5  -  CO  •  C6H5. 

Acetophenone,  Phenyl-methyl  ketone,  C6H5'CO«CH3,  is  the 
simplest  representative  of  the  mixed  aromatic  ketones.  It 
crystallizes  in  colourless  plates,  is  readily  soluble  in  water, 
melts  at  20°,  boils  at  200°,  and  is  obtained  by  the  normal 
modes  of  preparation  for  ketones,  e.g.  by  distilling  a  mixture 
of  acetate  and  benzoate  of  calcium,  as  also  by  the  Friedel- Crafts' 
synthesis  (p.  346),  viz.  the  conjoint  action  of  acetyl  chloride 
and  aluminium  chloride  upon  benzene.  When  benzene  and 
its  derivatives  are  converted  into  ketones  by  this  method, 
only  one  acyl  group  is  introduced  as  a  rule,  and  this  into  the 
para-position  with  respect  to  any  alkyl  group  already  present. 
With  a  sym.  trialkylated  benzene,  e.g.  mesitylene,  it  has  been 
found  possible  to  introduce  two  acyl  groups,  e.g.  diacetyl- 
mesitylene,  (CH3)306H(COCH3)2  (V.  Meyer,  B.  1895,  28,  3212; 
1896,  29,  846,  1413).  When  the  temperature  is  kept  low  by 
diluting  the  mixture  with  carbon  disulphide,  a  good  yield  of 
ketone  may  be  obtained  by  the  Friedel-Crafts'  method. 

Acetophenone  unites  in  itself  the  properties  of  a  ketone  of 
the  fatty  series  and  of  a  benzene  derivative.  It  yields  benzoic 
acid  and  carbon  dioxide  when  oxidized  with  ordinary  oxidizing 
agents,  but  with  cold  alkaline  permanganate  it  yields  C6H5- 
CO'C02H,  phenyl-glyoxylic  acid  or  benzoyl-formic  acid. 
When  warmed  with  halogens,  it  is  substituted  in  the  side 
chain  (e.g.  to  "phenacyl  bromide",  C6H5 •  CO •  CH2Br),  and 
with  nitric  acid  it  is  nitrated.  It  is  used  as  a  soporific  under 
the  name  of  "Hypnone".  Its  oxime  melts  at  59°,  and  its 
phenyl-hydrazone  at  105°. 

Although  it  combines  with  hydrogen  cyanide  to  form  the 
nitrile  of  a-phenyl-lactic  acid,  it  cannot  form  an  additive  com 
pound  with  sodic  hydric  sulphite. 

Its  homologues  closely  resemble  it,  but  are  liquid  at  the 
ordinary  temperature.  Acetophenone  and  some  of  its  homo- 
logues can  be  prepared  from  hydrocarbons  with  long  side 
chains  by  Etard's  reaction  (see  p.  424;  B.  23,  1070;  24,  1356). 
Aromatic  poly  ketones  (cf.  p.  221)  have  also  been  prepared,  e.g.^ 
benzoyl-acetone,  C6H5  •  CO  •  CH2  •  CO  •  CH3,  and  acetophenone- 
acetone,  C6H5  •  CO  -  CH2  •  CH2  •  CO  •  CH3.  The  latter,  like- 


428          XXV.   AROMATIC  ALCOHOLS,  ALDEHYDES,   ETC. 

acetonyl-acetone,  is  readily  converted  into  furane,  pyrrole,  and 
thiophene  derivatives  (see  p.  516). 

Benzaldehyde  condenses  with  acetone  and  acetophenone  in  the 
presence  of  alkalis,  yielding  unsaturated  ketones,  e.g.  Benzylid- 
eneacetone,  CHPh:CH«CO-CH3,  m.-pt.  41°,  and  benzylidene- 
acetophenone,  chakone,  CHPh  •  CH :  CH  •  CO  •  C6H5,  m.-pt.  58°. 

Benzophenone,  Diphenyl  ketone,  C6H5  •  CO  •  C6H5,  may  be 
obtained  (1)  by  distilling  calcium  benzoate,  (2)  by  the  Friedel- 
Crafts'  synthesis,  (3)  by  the  oxidation  of  diphenylmethane, 
(C6H5)2CH2,  or  of  diphenyl-carbinol,  (C6H5)2CH  •  OH. 

Good  yields  of  ketones  are  not  usually  obtained  by  the 
action  of  Grignard's  reagents  on  acid  chlorides;  as  a  rule  the 
reaction  proceeds  further,  and  a  tertiary  alcohol  is  obtained 
(p.  356).  An  exception  is  found  in  the  reaction  between 
a-naphthyl-magnesium  bromide  and  benzoyl  chloride. 

Ketones  have  recently  (Blaise,  C.  R  1901,  132,  38;  133,  299) 
been  synthesised  from  Gh'ignard's  reagents  and  nitriles,  e.g. : 

R-CN  +  B/.Mg.I  =  RR'CiNMgl, 

and  this  with  water  gives: 

R.CO-R'  +  NHS  +  I-Mg-OH. 

Acid  amides  react  in  a  somewhat  similar  manner. 

Benzophenone  is  dimorphous;  the  stable  modification  melts 
at  49°,  and  when  boiled  or  distilled  yields  the  unstable  modi- 
fication, melting  at  26°;  but  this  gradually  passes  back  again 
into  the  stable  modification.  The  reaction  is,  however,  con- 
siderably accelerated  by  the  addition  of  a  minute  crystal  of 
the  stable  compound.  It  yields  an  oxime  melting  at  140°  and 
a  phenyl-hydrazone  melting  at  105°. 

When  reduced  with  zinc  dust  or  hydriodic  acid  and  red 
phosphorus,  it  yields  diphenylmethane. 

Stereo-isomeric  Oxirnes  and  Hydrazones. — The  isomerism 
described  on  pp.  137  et  seq.  is  more  frequently  met  with  in  the 
aromatic  than  in  the  aliphatic  series.  Benzaldehyde  and  most 
of  its  substitution  products  yield  two  distinct  oximes  and  most 
of  the  unsymmetrical  aromatic  ketones,  e.^..^?-chloro-benzo- 
phenone,  06H4C1  •  CO  •  C6H6,  and  tolyl-phenyl-ketone,  CH3« 
C6H4«CO»C6H5,  also  yield  stereo-isomeric  oximes  of  the  syn- 
and  anti-  types.  The  one  isomeride  is  usually  readily  trans- 
formed into  the  more  stable  by  means  of  hydrochloric  acid  or 
bromine,  by  rise  of  temperature,  and  by  exposure  to  light. 


HYDROXY-ALCOHOLS,   ETC.  429 

The  following  relationships  of  the  benzaldoximes  are  of 
interest: — 

Benz-cwfo'-aldoxime    — *•    Benz-awft'-aldoxime  hydrochloride 
f  heated  J  heated 

Benz-syn-aldoxime      •*—    Benz-sytt-aldoxime  hydrochloride. 
—  HC1 

The  syn-  or  anti-  configuration  of  the  isomerides  is  determined 
in  the  case  of  the  aldoximes  by  a  comparison  of  the  readiness 
with  which  water  is  eliminated  and  a  nitrile  formed,  and  in 
the  case  of  the  ketoximes  by  an  examination  of  the  products 
obtained  by  Beckmanris  transformation  (p.  139).  Thus: 

C6H5.C.C6H4.CH3    gives    CGH6.CO.NH.C6H4.CH3 

"  Benz-#-toluidide 

Phenyl-^-tolyl-antt-ketoxime 
and 

C6H6.C.C6H4.CH3    gives  CH3.C6H4.(X).NH.C6H6 
"  Anilide  of  jp-toluic  acid. 

Phenyl-jj-tolyl-sj/n-ketojcime 

Compare  Henrich,  B.  1911,  44,  1533. 

D.  Hydroxy  or  Phenolic  Alcohols,  Aldehydes,  and 
Ketones 

Formula.  Name.  Constitution. 

OH.C6H4.CH2OH Saligenin, 

or    o-hydroxy-benzyl  alcohol. 

OCH3.C6H4.CH2OH Anisyl  alcohol, 

or    _p-methoxy-benzyl  alcohol. 
OH  •  C6H3(OCH8) .  CH2OH ....     Vanillic  alcohol, 

or    3-methoxy-4-hydroxy-benzyl 

alcohol. 
OH  •  C6H3(OCH3) (C8H4  •  OH)..    Coniferyl  alcohol, 

[OCHS:OH  =  3:4]. 

OH.C6H4.CHO :....     Salicyl-aldehyde, 

or    o-hydroxy-benzaldehyde. 

OCH8.C6H4.CHO Anisaldehyde, 

or    £>-methoxy-benzaldehyde. 

(OH)2C6H3 •  CHO Procatechuic  aldehyde, 

or    3 : 4-dihydroxy-benzaldehyde. 

OH.C6H3(OCH3).CHO Vanillin, 

or    3  -  methoxy  -  4  -  hydroxy  -  benz- 
aldehyde. 

CH202 :  CCH3  •  CHO Piperonal,  artificial  heliotrope 

or    methylene-protocatechuic  al- 
dehyde. 

A  large  number  of  compounds  are  known  which  possess 


430          XXV.   AROMATIC  ALCOHOLS,    ALDEHYDES,   ETC. 

phenolic  properties  in  addition  to  those  of  an  alcohol,  aldehyde 
or  ketone.  They  are  derived  from  the  simple  alcohols,  &c., 
by  the  entrance  of  hydroxyl  into  the  benzene  nucleus. 

Several  of  these  compounds  occur  in  nature,  e.g.  saligenin 
is  a  constituent  of  salicin  (see  the  Glucosides),  while  salicylic 
aldehyde  is  found  in  Spiraea  varieties  and  vanillin,  in  vanilla 
capsules.  Anisaldehyde  is  obtained  from  the  oxidation  of 
anisole  (methyl  phenyl  ether). 

An  extremely  interesting  synthesis  of  hydroxy-aldehydes  is 
by  the  Tiemann-Eeimer  reaction.  This  consists  of  heating  a 
phenol  with  chloroform  in  the  presence  of  concentrated  potas- 
sium hydroxide  : 

C6H6.OK  +  CHC13  =  HC1  +  CHC12.C6H4.OK, 


and  the  dichlor-derivative  thus  formed  is  hydrolyscd  by  the 
alkali  to  CHO.C6H4.OK.  The  formyl-group  -CH:0  always 
takes  up  the  o-  or  ^-position  with  respect  to  the  hydroxy- 
group,  and,  as  a  rule,  the  o-  and  jp-compounds  are  formed 
together,  and  may  often  be  separated  by  the  difference  in 
volatility  of  the  two  compounds  in  steam. 

Vanillin  crystallizes  in  beautiful  needles,  and  is  prepared 
on  the  large  scale  from  coniferin,  C16H2208  -f-  2H20,  a  com- 
pound occurring  in  the  sap  of  the  cambium  in  the  Coniferse. 
This  is  hydrolysed  by  acids  into  glucose  and  coniferyl  alcohol, 
C6H3(OH)(pCH3)(C3H4.OH),  and  the  latter  yields  vanillin 
when  oxidized  (Tiemann  and  Haarmann)  ',  the  CH3  group  is 
removed  by  heating  with  hydrochloric  acid  at  200°,  with  the 
formation  of  protocatechuic  aldehyde.  Vanillin  is  also  found 
in  asparagus,  raw  beet-sugar,  and  asafcetida,  and  it  likewise 
results  from  the  oxidation  of  olive  wood,  &c. 

Vanillin  can  also  be  obtained  synthetically  from  m-chloro- 
/>-nitro-benzaldehyde  (from  m-chloro-^-nitro-toluene). 

E.  Quinones 

Quinones  are  compounds  derived  from  benzene  and  its 
derivatives  by  the  replacement  of  two  atoms  of  hydrogen  by 
two  of  oxygen,  e.g.  C6H402.  As  a  group  they  are  characterized 
by  (a)  their  yellow  colour,  (b)  being  readily  reduced  to  dihydric 
phenols,  and  hence  often  acting  as  oxidizing  agents.  They  are 
often  divided  into  para-quinones,  in  which  the  two  oxygen 
atoms  are  in  the  ^-position,  and  ortho-quinones,  in  which  they 
are  in  the  0-position. 


^-BENZOQUINONE  431 

^-Benzoquinoae  or  Quinone,  C0H402  (1838),  is  produced 
when  chromic  acid  is  added  to  a  solution  of  quinol.  It  crys- 
tallizes in  yellow  needles  or  prisms  of  a  characteristic  pungent 
odour  something  like  that  of  nut-shells,  is  sparingly  soluble  in 
water  but  readily  in  alcohol  and  ether,  and  can  be  sublimed; 
m.-pt.  116°.  Corresponding  with  it  we  have  a  large  number 
of  higher  homologues,  &c.  These  also  are  solids,  mostly  of  a 
yellow  colour,  and  are  volatile  withrsteam;  they  are  obtained 
by  the  oxidation  of  the  corresponding  dihydroxy-phenols,  or 
of  polyhydric  pnenols,  which  contain  two  hydroxyls  in  the 
para-position. 

Quinone  is  also  formed  by  the  oxidation  of  many  aniline 
and  phenol  derivatives  belonging  to  the  para-series,  e.g. 
^-amino-phenol,  sulphanilic  acid,  and  £>-phenol-sulphonic  acid; 
it  is  usually  prepared  by  the  oxidation  of  aniline  itself  by 
means  of  chromic  acid  (see  B.  1887,  20,  2283).  It  was  first 
obtained  by  distilling  quinic  acid  with  manganese  dioxide  and 
sulphuric  acid.  Exposure  to  light  causes  it  to  turn  brown, 
and  it  colours  the  skin  yellow-brown.  It  is  readily  reduced 
to  quinol  by  S02,  HI,  SnCl2  and  HC1,  &c.,  and  can  therefore 
act  as  an  oxidizing  agent. 

In  chloroform  solution  it  takes  up  two  or  four  atoms  of 
bromine  to  form  a  di-  or  tetra-bromide  (C6H402»Br4).  Under 
other  conditions  chlorine  and  bromine  act  upon  it  as  substi- 
tuents,  while  hydrochloric  acid  forms  chloroquinol : 

C6H402  +  HC1  =  C6H3C1(OH)2. 

It  yields  sparingly  soluble  crystalline  compounds  with 
primary  amines,  and  also  coloured  compounds  with  phenols. 
With  quinol  it  forms  an  additive  compound  termed  quin- 
hydrone,  C6H402  +  C6H4(OH)2;  this  crystallizes  in  green 
prisms  with  a  metallic  lustre,  and  is  also  formed  as  an  inter- 
mediate product  in  the  oxidation  of  quinol  or  in  the  reduction 
of  quinone.  Its  constitution  has  not  been  definitely  settled. 
(Cf.  Siegnunds,  J.  pr.  1911,  83,  553;  also  Knorr,  B.  1911,  44, 
1503.) 

Constitution. — Quinone  is  derived  from  benzene  by  the  ex- 
change of  two  atoms  of  hydrogen  for  two  of  oxygen,  which, 
from  the  close  connection  between  quinone  and  quinol,  must 
be  in  the  ^-position.  The  constitution  of  quinone  may  be 
explained  either  by  assuming  that  these  two  oxygen  atoms 
are  linked  together,  as  in  peroxide  of  hydrogen,  H»0-0»H, 
so  that  the  benzene  nucleus  remains  unchanged,  or  that  the 


432          XXV.   AROMATIC  ALCOHOLS,   ALDEHYDES,   ETC. 

latter  experiences  a  partial  reduction,  with  the  formation  of  a 
derivative  of  C6H8,  a  "  diketo-dihydro-benzene  " : 

C  CO 

CH  .0         HC/NCH 


According  to  the  first  of  these  two  formulae,  quinone  would 
be  a  peroxide  ;  according  to  the  second,  a  ketone.  In  favour 
of  the  latter  view  (which  was  brought  forward  by  Fittig,  and 
is  now  almost  universally  accepted)  are  (1)  the  fact  that  qui- 

none can  be  converted  into  an  oxime,  C2H        ^ 


22 

(identical  with  nitroso-phenol,  p.  414),  and  into  a  dioxime, 
quinone  dioxime,  C2H2<^;oS>C2H2  (B.  20,  613);  (2)  its 

power  of  forming  additive  compounds  with  bromine;  and  (3) 
its  relations  to  the  analogously  constituted  anthraquinone. 
(Of.  B.  18,  568;  A.  223,  170;  J.  pr.  Ch.  42,  161.  Also  chapter 
on  Physical  Properties  and  Constitution.) 

Tetrahydro-quinone,  p-Diketo-hexamethylene  (cyclo-hexane-l-A- 
dione), 

CH2.CO.CH2 

CH2.CO-CH2' 

can  be  prepared  by  hydrolysing  and  eliminating  the  carboxyl 
groups  from  succinylo-succinic  ester  (p.  343).  It  crystallizes 
in  colourless  prisms,  melts  at  78°,  and,  on  reduction,  yields 
quinitol  (p.  419).  (Cf.  B.  22,  2168;  23,  1272.) 

Chloranil,  Tetrachloro-quinone,  CgCl402,  which  crystallizes  in 
lustrous  yellow  plates,  is  obtained  by  chlorinating  quinone  and 
also  by  oxidizing  many  organic  compounds,  e.g.  phenol,  with 
HC1  and  KC103.  A  good  yield  may  be  obtained  by  chlorinat- 
ing |?-nitraniline,  reducing  the  2  :  6-dichloro-4-nitraniline  thus 
obtained  to  2  :  6-dichloro-^-phenylene-diamine,  and  then  oxidiz- 
ing and  chlorinating  by  means  of  potassic  chlorate  and  hydro- 
chloric acid: 

N  02  •  C6H4  •  NH2  -*  N02  -  C6H2C12  •  NH2  —  C6H2C12(NH2)2  ->  C6C14O2 

(Witt.  Abstr.  1904,  1,  174.)  When  reduced,  it  yields  the 
colourless  tetrachloro-quinol;  it  also  acts  as  an  oxidizing  agent, 
converting  e.g.  dimethylaniline  into  methyl-violet.  A  dilute 


QUINONES  433 

solution  of  potassium  hydroxide  transforms  it  into  potassium 
chloranilate,  C6C1202(OK)2  +  H20  (dark-red  needles),  corre- 
sponding with  which  there  is  also  an  analogous  nitro-compound, 
potassium  nitranilate,  C6(N02)202(OK)2.  The  latter  salt  is  dis- 
tinguished by  its  sparing  solubility,  hence  its  formation  may 
be  made  use  of  as  a  test  for  potassium  compounds.  (For  its 
constitution,  see  B.  19,  2398.) 

Chlorine  transforms  chloranil  and  chloranilic  acid  into  com- 
plex chloro-products  of  the  hexa-  and  pentamethylene  series, 
and  finally  into  chlorinated  fatty  compounds.  (For  a  tabular 
summary,  see  Hantzsch,  B.  22,  2841;  cf.  also  B.  25,  827,  842.) 

Toluquinone,  C6H3(02)(CH3),  xyloquinone,  C6H2(O2)(CH3)2, 
thymoquinone,  C6H2(02)(CH3)(C3HT),  &c.,  are  known.  Several 
of  these  can  be  prepared  synthetically  by  the  condensation 
of  1:2  diketones;  for  instance,  diacetyl  yields  xyloquinone 
under  the  influence  of  alkali  (cf.  B.  21,  1411  and  p.  342): 

CHa-rCOj-CO-CHiHi:         _  CH^C-CO-CH 

"         HC.CO-C.CH3  4        2' 


0-Benzoquinone,    CO\IT  ^          ^^'    ^some"c   w^   tne 


j9-compound,  has  been  recently  prepared  by  Willstatter  and 
Pfannenstiel  (B.  1904,  37,  4744)  by  the  oxidation  of  an  ethereal 
solution  of  catechol  (0-dihydroxy-benzene)  with  silver  oxide. 
It  forms  pale-red  transparent  plates,  is  relatively  unstable, 
and  begins  to  decompose  at  60°-70°.  It  is  readily  reduced 
by  sulphur  dioxide  to  catechol,  and  dyes  the  skin  brown.  For 
two  isomeric  forms,  cf.  B.  1908,  41,  2580;  1911,  44,  2632. 

F.  Quinone  Chlorimides,  Quinone  Aniles, 
and  Anilino-quinones 

A  number  of  nitrogen  derivatives  closely  related  to  the 
quinones  are  known.  As  examples,  we  have  C6H4^Q  '  , 
quinone  chlorimide;  CfiH4Cxrni>  quinone  dichlorimide  ; 

•NT     OH 

C6H4^  ,  quinone  oxime,  and  the  corresponding  dioxime; 


<luinone  anile;  and  C6H4N.*C6H5'  (luinone 
dianile. 

The  quinone  chlorimides  are  obtained  by  the  oxidation  of 
the  ^-amino-phenols  or  ^>-phenylene-diamines  with  bleaching 

(B480)  8l5 


434  XXV.    AROMATIC  ALCOHOLS,    ALDEHYDES,   ETC. 

powder,  e.g.  quinone  chlorimide,  0:CgH4:NCl,  from  ^-amino- 
phenol  hydrochloride,  and  quinone  dicnlorimide,  C1«N:C6H4: 
N»C1,  from  ^-phenylene-diamine  hydrochloride.  The  first- 
named  crystallizes  in  golden-yellow  crystals,  which  are  volatile 
with  steam;  when  reduced  it  yields  amino-phenol,  and  when 
boiled  with  water  quinone;  the  dichorimide  reacts  similarly. 

Quinone  monoxime,  obtained  by  the  action  of  hydroxyl- 
amine  hydrochloride  on  quinone  (H.  Goldschmidt,  B.  1884,  17, 
213),  is  identical  with  the  compound  obtained  by  the  action 
of  nitrous  acid  on  phenol,  or  by  the  hydrolysis  of  ^-nitroso- 
dimethyl-aniline,  and  previously  termed  ^-nitroso-phenol.  It 
would  appear  to  have  the  oxime  constitution  0:CgH4:N'OH, 
as  with  hydroxylamine  it  yields  the  dioxime  OH»N:C6H4: 
N'OH,  and  when  alkylated  yields  ethers  of  the  type  0:C6H4: 
N-OK.  (Cf.  also  Hartley,  J.  C.  S.  1904,  1016.) 

Quinone  monanile  is  obtained  by  oxidizing  j9-hydroxy-di- 
phenylamine,  OH  •  C6H4  •  NH  •  CgH5,  and  forms  fiery-red  crys- 
tals melting  at  97°;  with  aniline  it  yields  dianilino-qumone 
anile,  0  :  C6H2(NHPh)2 :  NPh.  The  dianile  is  obtained  by- 
oxidizing  diphenyl  - p  -  phenylene  -  diamine,  C^H4(NHPh)2;  it 
melts  at  175°-180°,  and  its  dianilide,  viz.  dianilino- quinone 
dianile,  NPh :  C6Ho(NHPh)2 :  NPh,  is  most  readily  obtained  by 
heating  p-nitroso-dimethyl-aniline  with  aniline  and  aniline  hy- 
drochloride. Such  anilino-quinone  aniles  are  usually  termed 
azophenines  (Fischer  and  Hepp,  A.  1889,  256,  257;  1890,  262, 
247).  The  important  groups  of  aniline  dyes  known  as  indo- 
phenols  and  indamines  are  respectively  hydroxy-  and  amino- 
derivatives  of  these  aniles,  e.g.  phenol  blue  is  (CH3)2N«C6H4« 
N :  C6H4 : 0,  and  is  obtained  by  oxidizing  a  mixture  of  amino- 
dimethyl-aniline  and  phenol;  the  corresponding  a-naphthol  de- 
rivative, NMe2«C6H4»N:C10H7:0,  is  an  important  blue  dye. 

G.  Pseudo-phenols.    Methylene-quinones 

Numerous  phenolic  alcohols  react  with  halogen  hydracids 
yielding  the  corresponding  esters  of  the  alcohols,  e.g. : 

OH.C6H3Br.CH2.OH  —  OH.C6H3Br.CH2Br, 
OH.C6Br2Me2.CH2.OH  — -  OH.C6Br2Me2-CH2.Br; 

but  the  products  thus  obtained  are  insoluble  in  alkalis,  and  are 
characterized  by  the  reactivity  of  the  bromine  atom  in  the 
•  CH2Br  group.  The  compounds  have  been  termed  by  Auwers 
pseudo-phenols,  and  they  are  usually  regarded  as  o-  or  ^-quinone 


AROMATIC  ACIDS  435 

derivatives,  e.g.  the  two  compounds  mentioned  above  are  repre- 
sented as 


Such  compounds  readily  react  with  alkalis,  losing  hydrogen 
bromide  and  yielding  methylene  -  quinones  of  the  type 
0:C6H3Br:CHo;  the  majority  of  these  are  unstable,  and  im- 
mediately yield  condensation  products  which  are  insoluble  in 
alkalis  (cf.  Auwers,  A.  301,  203;  B.  32,  2978;  34,  4256;  36, 
1878;  39,  435;  Zincke,  A.  320,  145;  322,  174;  329,  1;  353, 
335,  357). 

XXVI  AROMATIC  ACIDS 

The  aromatic  acids  are  analogous  to  the  fatty  acids  in  most 
respects.  As  acids  they  are  capable  of  forming  exactly  the 
same  kinds  of  derivatives  as  the  latter,  e.g.  metallic  salts, 
esters,  chlorides,  anhydrides,  amides,  &c.: 


As  benzene  derivatives  they  yield  chloro-,  bromo-,  iodo-,  hy- 
Iroxy-,  nitro-,  amino-,  and  sulphonic  acid  derivatives,  &c.,  e.g.: 

C6H4C1-CO2H  (chloro-benzoic  acids); 
NH2'C6H4'CO2H  (amino-benzoic  acids); 
OH-S02-C6H4.CO2H  (sulpho-benzoic  acids); 
OH'C6H4«CO2H  (hydroxy-benzoic  acids); 
C0H6-CH(OH).CO2H  (mandelic  acid);  &c. 

Constitution. — Corresponding  with  the  aromatic  acids  there 
are  nitriles,  e.g.  with  benzoic  acid,  benzo-nitrile,  C6H5»C:N, 
which  may  also  be  regarded  as  cyanogen  derivatives  of  the 
lydrocarbons  (in  the  above  case,  cyano-benzene),  and  which, 
m  hydrolysis,  yield  the  i  acids.  From  this,  and  from  their 
general  properties,  it  follows  that  their  constitution  must 
;orrespond  exactly  with  that  of  the  fatty  acids;  like  the 
atter  they  are  characterized  by  the  presence  of  carboxyl, 
CO* OH,  in  the  molecule.  There  are  monobasic,  di-,  tri-, 
and  up  to  hexabasic  aromatic  acids,  according  to  the  number 
)f  hydrogen  atoms  in  the  molecule  which  are  readily  re- 
)laceable  by  metallic  radicals,  i.e.  according  to  the  number  of 
jarboxyl  groups: 

C6H4(C02H)2  C6H3(C02H)3  C6(CO2H)6 

Phthalic  acids  Benzene-tri-carboxylic  acids         Mellitic  acid. 


436  XXVI.   AROMATIC  ACIDS 

Numerous  unsaturated  aromatic  acids  are  known.  As  un- 
saturated  compounds,  they  readily  form  additive  compounds 
with  hydrogen,  chlorine,  hydrogen  iodide,  and  are  thereby 
converted  into  saturated  acids  or  their  substitution  products. 
In  most  of  these  additions  the  benzene  nucleus  remains  un- 
altered. Their  constitution  is  therefore  entirely  analogous  tc 
that  of  the  acids  of  the  acrylic  or  propiolic  series;  they  contain 
a  side  chain  with  a  double  or  triple  carbon  bond : 

C6H6  •  CH :  CH  •  C02H  C6H5  •  C :  C  -  CO2H 

Cinnamic  acid  Phenyl-propiolic  acid. 

In  addition  to  the  aromatic  acids  proper,  which  have  just 
been  mentioned,  other  acids  have  been  prepared  recently,  which 
are  derivatives  either  of  a  completely  reduced  or  a  partially  reducea 
benzene  molecule.  The  acids  of  the  former  series,  e.g.  the  hexa 
hydro-benzoic  acids,  have  properties  very  similar  to  those  oJ 
the  saturated  fatty  acids;  while  those  of  the  latter,  e.g.  the  di- 
and  tetrahydro-benzoic  acids,  resemble  the  unsaturated  fatty 
acids.  (Cf.  p.  349.) 

The  aromatic  hydroxy-acids,  e.g.  the  hydroxy-benzoic  acids, 
which  are  both  phenols  and  acids,  manifestly  contain  phenolic 
hydroxyl  (i.e.  hydroxyl  which  is  linked  directly  to  the  ben 
zene  nucleus)  in  addition  to  the  carboxyl  group  or  groups 
they  are  capable  of  yielding  salts  either  as  acids  or  as  phenols, 
but  otherwise  they  correspond  in  many  points  with  the  ali 
phatic  hydroxy-acids. 

The  true  aromatic  hydroxy-acids,  such  as  mandelic  acic 
(phenyl-gly collie  acid),  which  correspond  completely  with  the 
aliphatic  hydroxy-acids,  manifestly  contain  their  alcoholic  hy 
droxyl  not  in  the  benzene  nucleus,  but  in  the  side  chain,  as  is 
also  the  case  with  the  aromatic  alcohols. 

Nomenclature. — One  of  the  simplest  systems  of  nomenclature 
is  the  designation  of  the  aromatic  acids  as  carboxylic  acidi 
of  the  original  hydrocarbons  in  question,  e.g.  phthalic  acid  it 
benzene-1 : 2-dicarboxylic  acid.  Many  names,  such  as  xylic 
acid,  are  taken  from  those  of  the  hydrocarbons  into  whicl 
the  carboxyl  has  entered,  while  others,  such  as  mesitylenic 
acid,  indicate  the  hydrocarbons  from  which  the  acids  an 
obtained  by  oxidation.  An  important  principle  as  regards 
nomenclature  depends  upon  the  fact  that  aromatic  acids  car 
be  derived  from  almost  every  fatty  acid  of  any  consequence 
by  the  exchange  of  H  for  C6H6,  e.g. : 

CH3  •  CO2H  (acetic  acid)       C6Hg  -  CH2  •  CO2H  (phenyl-acetic  acid). 


FORMATION  OF  AROMATIC  ACIDS  437 

There  thus  exist  phenylated  acids  analogous  to  the  acids  of 
the  acetic,  glycollic,  succinic,  malic,  and  tartaric  series,  &c. 
For  example,  atropic  acid,  C6BL'C(C02H):CH2,  may  be  desig- 
nated a-phenyl-acrylic  acid,  ana  cinnamic  acid,  C6H6  •  CH  :  CH  • 
C02H,  /5-phenyl-acrylic  acid. 

Properties.  —  Most  of  the  aromatic  acids  are  solid  crystalline 
substances,  generally  only  sparingly  soluble  in  water,  and 
therefore  precipitated  by  acids  from  solutions  of  their  salts, 
but  often  readily  soluble  in  alcohol  and  ether.  The  simpler 
among  them  can  be  distilled  or  sublimed  without  decom- 
position, while  the  more  complicated,  especially  phenolic  and 
polycarboxylic  acids,  evolve  carbon  dioxide  when  heated; 
e.g.  salicylic  acid,  OH  •  C6H4  •  C02H,  breaks  up  into  phenol  and 
C02.  The  elimination  of  carbonic  anhydride  from  those  acids 
which  volatilize  without  decomposition  may  be  effected  by 
heating  with  soda-lime;  in  poly  basic  acids  the  carboxyls  may 
be  successively  decomposed  : 

C6H4(C02H)2  =  C6H6C02H  +  C02 


Occurrence.  —  A  large  number  of  the  aromatic  acids  are  found 
in  nature,  e.g.  in  many  resins  and  balsams,  and  also  in  the 
animal  organism  in  the  form  of  nitrogeneous  derivatives  such 
as  hippuric  acid  (benzoyl-glycocoll),  C6H5  •  CO  •  NH  •  CH2  •  C02H. 

Modes  of  Formation.  —  A.  Of  the  saturated  acids  :  — 

1.  By  the  oxidation  of  the  corresponding  primary  alcohols 
or  aldehydes,  e.g.  benzoic  acid  from  benzyl  alcohol,  or  from 
benzaldehyde. 

2.  One  of  the  commonest  methods  of  obtaining  aromatic 
acids  is  by  the  oxidation  of  benzene  homologues.     Each  alkyl 
group  present  in  the  nucleus  of  the  hydrocarbon  can  be  oxi- 
dized to  a  carboxylic  group,  whether  it  be  long  or  short,  e.g. 
both  C6H5.CH3  and  C6H5.CH2.CH2.CH3  yield  C6H5.C02H. 

All  substituted  benzene  homologues  which  contain  the  sub- 
stituent  in  the  side  chain  are  similarly  oxidized  to  non-substi- 
tuted aromatic  acids,  e.g.  C6H5-CH2C],  C6H5.CH2-NH2,  and 
C6H5.CH:CH.C02H  yield  C6H5.C02H. 

A  substituted  benzene  homologue  which  contains  halogen, 
nitro-,  sulpho-,  amino-,  hydroxy-,  &c.,  substituents  attached  to 
the  benzene  nucleus,  yields  a  similarly  substituted  aromatic 
acid,  e.g.-.  C6H4C1.CH3  —  C6ELC1.CO2H; 

(OH)2C6H3.CH3  —  (OH)2.C6H3.C02H; 
—  NO2.C6H4.CO2H. 


N02-C6] 
Should  there  be  several  side  chains  in  the  molecule,  they 


438  XXVI.   AROMATIC  ACIDS 

are  usually  all  converted  directly  into  carboxyl  by  chromic 
acid;  whereas  by  using  dilute  nitric  acid,  this  transformation 
can  be  effected  step  by  step,  e.g.  : 

C6H4(CH3)2   yield  first   C6H4(CH3)(CO2H)   and  then    C6H4(CO2H)2 
The  xylenes  Toluic  acids  Phthalic  acids. 

Nevertheless,  the  three  classes  of  isomeric  benzene  deriva 
tives  with  two  side  chains  comport  themselves  differently. 
The  para-compounds  are  the  most  readily  oxidized  to  acids  by 
chromic  acid  mixture,  and  then  the  meta-;  whereas  the  ortho 
compounds  are  either  completely  destroyed  by  it  (p.  348),  or 
not  attacked  at  all.  The  last-named  may,  however,  be  oxi- 
dized in  the  normal  manner  by  nitric  acid  or  potassic  perman- 
ganate. The  entrance  of  a  negative  group  or  of  hydroxyl  into 
the  o-position  with  respect  to  the  alkyl  radical  renders  the  oxi- 
dation more  difficult  (cf.  p.  416). 

3.  By  the  hydrolysis  of  the  corresponding  nitriles  : 

C6H6.CN-f-2H20  =  C6H5-CO2H-fNH3. 

These  nitriles,  which  can  be  prepared  from  the  ammonium 
salts  of  the  acids  in  the  same  manner  as  those  of  the  fatty 
series,  are  often  obtained  by  the  following  syntheses:  — 

(a)  By  distilling  the  potassic  salts  of  the  sulphonic  acids 
with  potassic  cyanide  or  ferrocyanide  (Merz\  just  as  the 
nitriles  of  the  fatty  acids  are  formed  from  the  potassium 
alkyl-sulphates  (p.  100): 

C6H6.S03K 


Nitriles  cannot,  as  a  rule,  be  prepared  from  KCN  and  aro 
matic  halogen  derivatives  which  contain  the  halogen  attached 
to  the  nucleus  (cf.  p.  355);  the  halogen  is  more  readily  re- 
placed by  cyanogen  if  sulphonic  acid  or  nitro-groups  are  like- 
wise present: 

C6H4Br.N02  +  KCN  =  CN.C6H4-N02  +  KBr. 


Benzyl  chloride,  C6H5'CH2C1,  and  all  the  haloid  hydro- 
carbons which  are  substituted  in  the  side  chain,  on  the  other 
hand,  react  with  potassic  cyanide  in  the  manner  characteristic 
of  the  alphyl  haloids  : 

C6H6.CH2C1  +  KCN  =  KCl-f  C6H6.CH2-CN 

Benzyl  cyanide. 

(b)  By  diazotizing  the  primary  amines  and  replacing  the 
diazo-group  by  cyanogen,  according  to  Sandmeyer's  reaction 


FORMATION  OF  ACIDS  439 

(p.  388).  This  reaction  is  frequently  made  use  of  in  the 
preparation  of  substituted  benzo-nitriles,  e.g.  2  :  4-dibromo- 
benzo-nitrile,  CgH^FoCN,  and  the  isomeric  2  :  6  -compound, 
also  of  tolu-nitriles,  CH3-C6H4.CN. 

(c)  By  heating  the  mustard  oils  (phenyl-iso-thiocyanates, 
p.  276),  with  copper  or  zinc  dust  (ffreitti): 


C6H5.N:C:S  +  2Cu  =  C6H6.C:N  +  Cu2S. 

(d)  By  the  molecular  transformation  of  the  isomeric  iso- 
nitriles  at  a  somewhat  high  temperature: 

C6H6.N:C  —  C6H6.C:N. 

(e)  By  eliminating  the  elements  of  water  from  the  oximes  of 
the  aldehydes  by  means  of  acetyl  chloride  (pp.  137  and  429): 

Benzaldoxime,  C6H6  •  CH  :  N  .  OH  =  C6H6  •  CN  -f  H2O. 

4.  By  the  reduction  of  unsaturated  acids,  thus  hydrocinnamic 
by  the  reduction  of  cinnamic  acid  with  sodium  amalgam  find 
water,  or  with  hydrogen  and  finely  divided  Palladium  : 

C6H6.CH:CH.CO2H  +  2H  =  C6H5.CH2.CH2-CO2H. 

The  acids  obtained  by  this  method  always  contain  the  C02H 
group  attached  to  a  side  chain.  Similar  acids  can  also  be  ob- 
tained by  the  reduction  of  hydroxy-,  bromo-,  or  keto-acids, 
where  the  OH,  Br,  CO,  and  C02H  are  all  in  side  chains,  e.g.  : 

C6H5.CH(OH).CO2H  —  C6H5.CH2.CO2H. 

5.  A  number  of  syntheses  of  nucleus  carboxylic  acids  can 
be  accomplished.     These  may  be  regarded  as  the  more  or  less 
direct  introduction  of  the  carboxylic  group  into  the  benzene 
nucleus,  and  are  usually  effected  by  means  of  carbonic  acid 
derivatives.     In  many  cases  the  yields  are  only  small,  and  the 
reactions  are  mainly  of  theoretical  interest. 

(a)  Benzoic  acid  and  its  homologues  are  produced  by  the 
action  of  carbon  dioxide  upon  bromo-benzenes,  &c.,  in  presence 
of  sodium  (Kehttt)  : 

C6H6Br  +  CO2  +  2Na  =  CflH6.CO2Na  +  NaBr. 

(b)  By  the  action  of  phosgene,  COC12,  upon  benzene  and  its 
homologues  in  presence  of  A1C13  (Friedel  and  Crafts)  : 

COC12  =  C6H6.COC1 


440  XXVL   AROMATIC  ACIDS 

Acid  chlorides  are  first  formed,  but  can  be  readily  decomposed 
by  water.  By  the  further  action  of  these  chlorides  upon  benzene 
in  presence  of  A1C13,  ketones  are  formed  (see  Benzo-phenone). 
Carbonyl  chloride  reacts  most  readily  with  tertiary  amines: 

=  (CH3)2N.C6H4.COC1 


(c)  By  the  action  of  carbamic  chloride,  C1-CO-NH2,  upon 
benzene  (or  phenol)  in  presence  of  A1C13,  amides  of  the  aro- 
matic acids  are  formed,  and  these  can  be  hydrolysed  (Gaiter- 
man,  B.  1899,  32,  1116): 

C6H6-fCl.CO.NH2  =  C6H6.CO-NH2 


(d)  By  the  action  of  sodium  upon  a  mixture  of  a  brominated 
benzene  and  ethyl  chloro-carbonate  (Wurtz);  in  this  case  the 
esters  are  first  formed,  but  these  are  readily  hydrolysed: 

6  +  NaBr  -f  NaCl. 


(e)  The  phenolic  acids  are  formed  by  passing  carbon  dioxide 
over  heated  sodium  phenates  (Kolbe-,  see  Salicylic  acid): 


In  the  case  of  the  polyhydroxy-phenols,  e.g.  resorcinol,  an  acid 
is  often  formed  by  merely  heating  the  phenol  with  a  solution 
of  ammonium  carbonate  or  potassium  bicarbonate  (B.  13,  930). 

(/)  jo-Hydroxy-acids  are  formed  by  the  action  of  carbon 
tetrachloride  upon  phenols  in  alkaline  solution  (B.  10,  2185; 
Tiemann-Beimer  reaction;  cf.  p.  430): 

C6H6.ONa  +  CC14  =  C6H4(OH).CC13  +  NaCl. 

C6H4(OH).C02Na  +  SNaCl  -f  2H20. 


(g)  By  heating  the  sulphonates  with  sodium  formate  (V. 
Meyer)  : 

C6H6.S03Na  +  HCO2Na  =  C6H6-C02Na  -j-HS03Na. 

(h)  By  the  action  of  carbon  dioxide  on  ethereal  solutions  of 
organo-magnesium  compounds  (Grignard's  reagents),  and  sub- 
sequent treatment  with  acids: 

C6H6.Mg.Br  +  C02  ->  C6H6.CO2'MgBr  —  C6H6.CO2H. 

6.  Syntheses  by  the  aid  of  ethyl  aceto-acetate  and  ethyl 
malonate. 

Ethyl  aceto-acetate  reacts  with  the  halide  derivatives  which 
are  substituted  in  the  side  chain,  e.g.  benzyl  chloride,  exactly 


FORMATION  OF  ACIDS 


as  in  the  fatty  series,  with  the  formation  of  the  more  com- 
plicated ketonic  acids,  which  again  are  capable  of  undergoing 
either  the  "acid  hydrolysis"  or  the  "ketone  hydrolysis" 
(p.  226),  e.g.-. 


C8H6  •  CHoCl  +  CH,  •  CO  •  CHNa  •  CO2Et 

=  CH3.CO.CH(CH2C6H6).C02Et  + 

Benzyl-aceto-acetic  ester. 

CH3.CO.CH(CH2.C6H5).C02Et  -f  2H2O 

=  C6H6.CH2.CH2.C02H  +  CH3.C02 

/3-Phenyl-propionic  acid. 

Ethyl  phloroglucinol  dicarboxylate,  (OH)3  •  C§H(C02Et)2, 
may  be  synthesised  by  heating  ethyl  sodio-malonate  with 
ethyl  malonate  at  145°  (Movre,  J.  C.  S.  1904,  165). 

7.  Hydroxy-acids  and  keto-acids  are  formed  by  exactly  the 
same  methods  as  in  the  fatty  series  (pp.  205  and  206),  e.g. 
mandelic  acid  by  the  combination  of  hydrogen  cyanide  with 
benzaldehyde,  and  hydrolysis  of  the  nitrile  thus  formed  (B.  14, 
239,1965): 

C6H5.CHO  +  HCN  =  C6H5.CH(OH).CN; 

or  from  phenyl-chloro-acetic  acid  (B.  14,  239): 

=  C6H5.CH(OH).CO2H  +  KC1. 


B.  The  following  are  some  of  the  commoner  methods  em- 
ployed for  the  preparation  of  unsaturated  acids:  — 

1.  From  the  mono-haloid  substitution  products  of  the  satu- 
rated acids  by  the  elimination  of  halogen  hydracid  (cf.  p.  163); 
also  from  the  corresponding  nitriles,  primary  alcohols,  &c.,  as 
in  the  case  of  the  saturated  compounds. 

2.  According  to  the  so-called  Perkin  synthesis,  by  the  action 
of  aromatic  aldehydes  upon  the  sodium  salts  of  fatty  acids  in 
the  presence  of  a  condensing  agent,  usually  acetic  anhydride. 
Thus,  when  benzaldehyde  is  heated  with  acetic  anhydride  and 
sodium  acetate,  cinnamic  acid  is  formed  : 


The  acetic  anhydride  probably  acts  as  a  dehydrating  agent 
in  this  instance,  the  reaction  taking  place  between  the  sodium 
acetate  and  the  aldehyde  (cf.  A.  216,  101).  Hydroxy-acids  are 
formed  as  intermediate  products  by  a  reaction  similar  to  the 
"aldol  condensation"  (p.  131);  in  the  above  case,  for  instance, 
£-phenyl-hydracrylic  acid,  C6H5  .  CH(OH)  .  CH2  .  C02H. 


442  XXVI.    AROMATIC  ACIDS 

When  the  sodium  salt  and  the  anhydride  of  two  different 
acids,  e.g.  sodic  propionate  and  acetic  anhydride,  are  used,  the 
product  varies  with  the  conditions  (B.  1901,  34,  918),  but 
usually  consists  of  a  mixture  of  two  unsaturated  acids. 

This  reaction  also  takes  place  with  the  hydroxy-aldehydes, 
with  the  homologues  of  acetic  acid,  and  also  with  dibasic  acids, 
e.g.  malonic;  but  all  acids  employed  must  contain  a  CH2  group 
in  the  a-position  with  respect  to  the  C02H,  e.g.  : 

C6H5.CH:0  +  CH3.CH2.C02Na  =  H2O-f  C6H6.CH:C(CH3).C02H 

a-Methyl-cinnamic  acid. 

It  is  a  very  general  mothod  used  for  the  preparation  of 
<x:/?-unsaturated  acids;  in  certain  cases,  e.g.  a-phenyl-cinnamic 
acid,  C6H5»CH:C(C6H5)«C02H,  and  its  nitro-derivatives,  two 
stereo-isomerides  are  produced  corresponding  with  the  two  cro- 
tonic  acids  or  with  fumaric  and  maleic  acid. 

Unsaturated  monobasic  acids  are  also  formed  when  aromatic 
aldehydes  are  heated  with  malonic  acid  in  presence  of  ammonia, 
aniline,  or  other  amines  (Knoevenagel)  : 

C6H6.CH:'O'+H2;C(CO2H)2  =  C6H6-CH:C(CX)2H)2 
=  CflH5  -  CH  :  CH  •  C02H  +  CO^ 

The  esters  of  these  acids  are  formed  when  aromatic  aldehydes 
are  condensed  with  the  esters  of  fatty  acids  in  the  presence  of 
sodium  ethoxide  (Claisen,  B.  23,  976;  cf.  Claisen  condensation, 
p.  224). 

3.  Uinnamic  acid  is  also  formed  by  the  action  of  benzal 
chloride  upon  sodium  acetate  (Caro): 

=  C6H5.CH:CH.C02H  +  2HC1. 


4.  By  the  action  of  aceto-acetic  ester  upon  the  phenols  in 
presence  of  concentrated  H2S04,  unsaturated  phenolic  acids  or 
their  anhydrides  (B.  16,  2119;  17,  2191)  are  formed,  e.g.: 


(Pseudo-form)  Methyl-cumarin. 

A.  Monobasic  Aromatic  Acids 

Constitution  and  Isomers.  —  The  cases  of  isomerism  in  the 
aromatic  acids  are  easy  to  tabulate.  An  isomer  of  benzoic 
acid  is  neither  theoretically  possible  nor  actually  known. 
Carboxylic  acids  of  the  formula  C8H802  may,  however,  be 


MONOBASIC  AROMATIC  ACIDS 


443 


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444  XXVI.   AROMATIC  ACIDS 

derived  from  toluene  by  the  entrance  of  carboxyl  either  into 
the  benzene  nucleus  or  into  the  side  chain,  thus  : 


o-m-p- 


C6H6.CH2.C02H 

Phenyl-acetic  acid. 


The  nature  of  their  oxidation  products  yields  proof  of  their 
constitution,  the  former  yielding  the  phthalic  acids,  and  the  latter 
benzoic. 

Of  acids  C9H1002,  a  large  number  of  isomers  are  already 
known  (see  table).  Hydrocinnamic  acid  and  hydratropic  acid 
are  phenyl-propionic  acids,  the  former  ft-  and  the  latter  a-, 
corresponding  with  the  lactic  acids;  the  isomeric  relations  of 
the  fatty  acids  thus  repeat  themselves  here.  The  tolyl-acetio 
acids,  CH3-CgH4-CH2-C02H,  and  the  ethyl-benzoic  acids, 
C2H5»C6H4»C02H,  stand  in  much  the  same  relation  to  each 
other  as  aceto-acetic  acid,  CH3  •  CO  •  CH2  •  C02H,  to  propionyl- 
formic  acid,  CoH6  •  CO  •  C02H,  and  they  all  yield  phthalic  acids 
when  oxidized.  Lastly,  mesitylenic  acid  and  its  isomers  are 
dimethyl-benzoic  acids,  and  are  oxidizable  to  benzene-tricarb- 
oxylic  acids. 

As  instances  of  isomers  among  the  unsaturated  acids,  we  may 
take  cinnamic  and  atropic  acids  (analogous  to  ft-  and  a-chlor- 
acrylic  acids,  p.  168). 

Further,  the  hydroxy-toluic  acids,  C6H3(CH3)(OH)(C02H), 
are  isomeric  with  mandelic  acid,  C6H5'CH(OH)-COoH,  the 
former  being  oxidized  to  hydroxy-phthalic  acids,  C6H3(OH) 
(C(XH)2,  and  the  latter  to  benzoic  acid;  the  hydrocoumaric  acids, 
CgIL003,  are  likewise  isomeric  with  tropic  acid.  The  first-named 
yield  hydroxy-benzoic  acids  on  oxidation,  and  the  last  benzoic. 

Differences  are  apparent,  e.g.  in  respect  to  reducibility, 
according  as  the  carboxyl  is  linked  directly  to  the  nucleus  or 
to  a  side  chain;  the  amides  of  the  respective  acids  are  in  the 
former  case  reduced  to  the  corresponding  alcohols,  but  not  in 
the  latter.  (Of.  B.  24,  173.) 

1.  MONOBASIC  SATURATED  ACIDS 

Benzoic  acid,  C6H5-C02H,  was  discovered  in  gum  benzoin 
in  1608,  and  prepared  from  urine  by  Scheele  in  1785.  Its 
composition  was  established  by  Liebig  and  Wohlei^s  classical 
researches  in  1832.  It  occurs  in  nature  in  gum  benzoin, 
from  which  it  may  be  obtained  by  sublimation  ("acidum 
benzoicum  ex  resina");  also  in  dragon's-blood  (a  resin),  in 
Peru  and  Tolu  balsams,  in  castoreum,  and  in  cranberries.  I* 


BENZOIC  ACIDS  445 

is  present  in  the  urine  of  horses  in  combination  with  glycocoll 
as  hippuric  acid,  from  which  it  may  be  obtained  by  hydrolysis 
with  hydrochloric  acid  ("acidum  benzoicum  ex  urina").  It 
is  obtained  on  the  large  scale  ("ac.  benz.  ex  toluole")  as  a 
by-product  in  the  manufacture  of  oil  of  bitter  almonds  from 
benzyl  chloride  or  benzal  chloride.  The  acid  may  also  be 
formed  by  heating  benzo-trichloride  with  water  to  a  some- 
what high  temperature: 

C6H6.CC13  —  C6H6.qOH)3  —  C6H6.CO.OH. 

Benzoic  acid  is  also  present  in  coal-tar.  It  crystallizes  in 
colourless  glistening  plates  or  flat  needles,  sublimes  readily, 
and  is  volatile  with  steam;  its  vapour  has  a  peculiar  irritating 
odour,  and  gives  rise  to  coughing.  It  melts  at  121°,  boils  at  250°, 
and  is  readily  soluble  in  hot  water,  but  only  sparingly  in  cold. 
When  heated  with  lime,  it  is  decomposed  into  benzene  and  car- 
bon dioxide.  It  is  used  in  medicine  and  in  the  manufacture  of 
aniline  blue.  Some  of  its  salts  crystallize  beautifully,  e.g.  cal- 
cium benzoate,  (C6H5  •  C02)2Ca  -f-  3  H20,  in  glistening  prisms. 

From  the  partially  or  wholly  reduced  benzene  molecule 
there  are  derived  (a)  the  dihydro-benzoic  acids,  C6H7'C02H, 
of  which  five  are  theoretically  possible,  according  to  the 
position  of  the  double  linkings,  viz.  A-l:3-,  A-l:4-,  A-l:5-, 
A-2:4-,  and  A-2 : 5-dihydro-benzoic  acids,  but  only  two  known 
(B.  1891,  24,  2623,  and  1893,  26,  454);  (b)  the  tetrahydro- 
benzoic  acids,  C6H9»C02H,  all  three  of  which  are  actually 
known,  viz.  A-1-,  A-2-,  and  A-3-tetrahydro-benzoic  acids  (A. 
271,  231);  and  a  hexahydro-benzoic  acid,  C6Hn«C02H  (hexa- 
Tnethylene-carboxylic  acid),  which  is  found  in  the  petroleum  from 
Baku,  and  which  can  also  be  prepared  from  benzoic  acid. 

The  Esters,  e.g.  methyl  benzoate,  C6H5.C02CH3,  b.-pt.  199°, 
and  ethyl  benzoate,  C6H5.C02C2H5,  b.-pt.  213°,  are  always 
prepared  by  the  catalytic  method  of  esterification  (p.  174), 
namely,  by  boiling  the  acid  for  three  to  four  hours  with  a 
3-per-cent  solution  of  dry  hydrogen  chloride  or  of  concentrated 
sulphuric  acid  in  the  requisite  alcohol  (E.  Fischer  and  Speier, 
B.  1895,  28,  3252).  They  may  also  be  obtained  by  the  other 
general  methods  for  the  preparation  of  esters :  (a)  by  the  action 
of  an  acid  chloride  on  the  alcohol  alone,  or  in  presence  of  alkali 
(Schotten,  Baumanri)  or  of  pyridine  (Emhorn  and  Hollandt, 
Abstr.  1899,  1,  577);  (b)  by  the  action  of  an  alkyl  iodide  on 
the  silver  salt  of  the  acid;  and  (c)  by  the  action  of  alkyl 
sulphates,  more  especially  methyl  sulphate,  on  aqueous  solu- 


446  XXVI.    AROMATIC  ACIDS 

tions  of  the  alkali  salts  of  the  acids  (Werner  and  Seybold,  B. 
1904,  37,  3658).  These  esters  are  liquids  of  pleasant  aromatic 
odour  which  boil  for  the  most  part  without  decomposition, 
and  frequently  serve  for  the  recognition  and  estimation  of 
alcohols.  They  may  be  hydrolysed  in  much  the  same  mariner 
as  the  aliphatic  esters,  although  as  a  rule  not  so  readily. 

Benzyl  benzoate,  C6H6»C02-CH2'C6H5,  is  present  in  the 
balsams  of  Peru  and  Tolu. 

Benzoyl  chloride,  C6H5.CO-C1  (LieUg  and  jrtiMer),  ob- 
tained by  the  action  of  phosphorus  pentachloride  on  the  acid, 
is  the  complete  analogue  of  acetyl  chloride,  but  more  stable 
than  the  latter,  since  it  is  only  slowly  hydrolysed  by  cold 
water,  although  quickly  by  hot.  It  is  a  colourless  liquid 
boiling  at  198°,  and  has  a  most  characteristic  pungent*  odour. 
It  is  prepared  technically  by  chlorinating  benzaldehyde. 

Benzole  anhydride,  (C6H5'CO)20  (Gerhardt\  is  exactly 
analogous  to  acetic  anhydride.  It  crystallizes  in  prisms  in- 
soluble in  water,  boils  without  decomposition,  and  becomes 
hydrated  on  boiling  with  water.  M.-pt.  39°. 

In  addition  to  the  ordinary  anhydrides  or  oxides,  peroxides 
of  the  type  benzoyl  peroxide  or  benzo-peroxide,  C6H5»CO»0- 
0  •  CO  •  C6H5,  are  known.  They  may  be  obtained  by  the  action 
of  the  acid  chloride  on  a  cooled  solution  of  sodic  peroxide 
(B.  1900,  33,  1575,  and  C.  C.  1899,  2,  396).  Benzo-peroxide 
crystallizes  from  alcohol  in  prisms,  melts  at  106°-108°,  is 
relatively  stable,  and  is  insoluble  in  water.  When  its  ethereal 
solution  is  mixed  with  sodic  ethoxide,  the  products  formed 
are  ethyl  benzoate,  and  the  sodic  salt  of  perbenzoic  acid, 
C6H6.CO'O.OH,  a  hygroscopic  acid  melting  at  41°-43°.  It 
has  a  strong  odour  resembling  hypochlorous  acid,  is  readily 
volatile,  but  decomposes  violently  when  heated,  and  is  a 
strong  oxidizing  agent  Many  aliphatic  and  aromatic  acids 
yield  similar  derivatives. 

Benzamide,  CgH^CO-NHg,  corresponds  with  acetamide,  and 
is  prepared  from  benzoyl  chloride  and  ammonia  or  ammonium 
carbonate.  It  forms  lustrous,  nacreous  plates,  melting  at  130°, 
boils  without  decomposition,  and  is  readily  soluble  in  hot  water. 

The  amido-hydrogen  of  benzamide  may  be  substituted  by 
alkyl  radicals  such  as  phenyl,  &c.,  with  the  formation,  e.g.  of 
benzanilide,  C?H5»CCKNHC6II5,  the  anilide  of  benzoic  acid, 
a  compound  which  can  be  readily  prepared  from  aniline  and 
benzoic  acid,  or  aniline  and  benzoyl  chloride.  It  crystallizes 
in  colourless  plates,  melts  at  158°,  distils  unchanged,  and  is  in 


BENZOIC  ACID  DERIVATIVES  447 

fact  the  complete  analogue  of  acetanilide,  but  is  much  more 
difficult  to  hydrolyse,  fusion  with  potash  being  one  of  the  best 
methods. 

Thio-benzamide,  C6H5.CS-NH2,  is  obtained  by  the  union 
of  benzo-nitrile  with  hydrogen  sulphide,  or  by  heating  benzyl- 
amine  with  sulphur. 

Benzoyl-hydrazine,  Benzhydrazide,  C6H5-CO.NH.NH2,  ob- 
tained from  ethyl  benzoate  and  hydrazine  hydrate,  melts  at 
112°,  and  with  nitrous  acid  yields  benzoyl-azimide,  benzazide, 
N 

|| ,  which  yields  benzoic  and  hydrazoic  acids  on 
N" 
hydrolysis.     (Cf.  Curtius,  Abstr.  1895,  1,  32.) 

Metallic  derivatives  of  benzamide  are  also  known,  e.g.  ben- 
zamide silver.  Titherley  (J.  C.  S.  1897,  468;  1901,  407)  has 
shown  that  the  silver  derivative  exists  in  two  forms :  a  white 

l^TTT 

compound,  which  is  stable  and  is  probably  C6H5*C<T;^  ,  and 

UAg 

an  unstable  orange  compound,  C6H5  •  CO  •  NH Ag.  These  two 
metallic  derivatives  correspond  with  the  pseudo  and  normal 

formulae  for  benzamide,  viz.  C6H5-(X%vTT  and  CgHg-CO'NH^ 

From  the  pseudo  form  are  derived  imino-ethers  (cf.  p.  185). 

Hippuric  acid,  Benzamino-acetic  acid,  C6IL«CO'NH»CH2« 
C02H,  is  an  amino-derivative  of  benzoic  acia,  being  derived 
from  the  latter  and  glycocoll  (amino-acetic  acid);  it  may  be 
prepared  by  heating  benzoic  anhydride  with  glycocoll  (B.  17, 
1663),  and  is  present  in  the  urine  of  horses  and  of  other  her- 
bivora.  When  benzoic  acid  or  toluene  is  taken  internally,  it 
is  eliminated  from  the  system  in  the  form  of  hippuric  acid. 
It  crystallizes  in  rhombic  prisms,  sparingly  soluble  in  cold 
water  but  readily  in  hot,  decomposes  when  heated,  and  forms 
salts,  esters,  nitro-derivatives,  &c.  When  hydrolysed  with  con- 
centrated hydrochloric  acid  it  yields  glycocoll  hydro'chloride 
and  benzoic  acid. 

Benzo-nitrile,  C6H5CN  (cf.  p.  438),  is  an  oil  which  smells 
like  oil  of  bitter  almonds,  and  boils  at  191*.  It  is  prepared 
either  by  the  action  of  PC15  upon  benzamide  (p.  183),  or  by 
distilling  benzoic  acid  with  ammonium  thiocyanate.  It  pos- 
sesses all  the  properties  of  a  nitrile,  combining  slowly  with 
nascent  hydrogen  to  benzylamine,  readily  with  halogen  hydride 
to  an  imino-chloride,  with  amines  to  amidines  (p.  1 87 ;  cf .  A. 
192,  1),  with  hydroxylamine  to  amidoximes  (p.  188). 


448  XXVI.   AROMATIC  ACIDS 

Substituted  Benzole  Acids.  —  The  hydrogen  atoms  of  ben- 
zoic  acid  are  replaceable  by  halogen  with  the  formation  e.g. 
of  chloro-benzoic  acid,  06H4C1»C02H.  In  such  formation  of 
mono-substitution  products  the  halogen  takes  up  the  meta- 
position  with  respect  to  the  carboxyl.  Nitric  acid  (especially 
a  mixture  of  nitric  and  sulphuric  acids)  nitrates  it  readily, 
w-nitro-benzoic  acid  being  the  chief  product,  together  with  a 
smaller  quantity  of  the  ortho-  and  a  very  little  of  the  para-acid. 

The  o-  and  ^-halogen  and  nitro-compounds  are  usually  pre- 
pared by  indirect  methods,  e.g.  : 

o-CH3.C6H4.N02  —  C02H.C6H4.NO2 
or     2:4-C6H3Br2.NH2  -*  C6H3Br2.CN  —  -  C6H3Br2.CO2H. 

In  the  preceding  pages  attention  has  been  drawn  repeatedly 
to  the  influence  which  a  radical,  already  present  in  the  benzene 
molecule,  exerts  on  the  position  taken  up  by  a  second  radical 
entering  the  molecule.  As  examples  we  have: 

CeHjBr         —  *  ^-C8H3r2;  CeH5-OH     —  *  o-o-2>-C6H2Br8-OH. 

C6H5.NOa     —  -  m-CoH^NOsk;      C6H5.NH2    -*  o-o-p-C6H2Br8-NH2. 

C,H6.S08H  —  m-C8H4(SO,H)2;    C6H5.CHO  —  w-N02-C6H4.CHO. 

C6H5  •  CH8    —  *  o-  and  p-CH8  •  CeH*  •  N02. 


The  following  broad  generalizations  will  be  found  to  apply 
to  most  cases:  — 

I.  If  the  radical  already  present  is  Cl,  Br,  I,  OH,  NH2,  01 
CH3,  then,  by  the  introduction  of  Cl,  Br,  I,  N02,  or  S03H 
radicals,  para-  and  to  a  certain  extent  ortho-compounds  are 
formed,  and  only  very  exceptionally  meta-compounds. 

II.  If  the  radical  present  is  NO,,  SOgH,  OHO,  or  C02H, 
then,  on  chlorination,  bromination,  nitration,  or  sulphonation, 
meta-compounds  are  formed.     (See  Crum  Brown  and  Gibson, 
J.  C.  S.  1892,  367.    For  details  cf.  Obermuller  ;  Hollemann,  Die 
Direkte  Einfiihrung  von  Substituenten,  1910.) 

In  many  reactions  all  three  isomeric  products  have  been 
isolated,  but  in  very  different  quantities;  thus  at  0°  benzoic 
acid  yields  80*2  per  cent  of  m-t  18'5  of  o-,  and  only  1*3  of 
jp-nitro-benzoic  acid;  at  30°  nitrobenzene  yields  91  per  cent  of 
m-,  8  of  0-,  and  1  of  p-dinitro-benzene.  It  is  probable  that 
the  three  isomerides  are  also  formed  in  other  cases  which  have 
not  been  examined  so  carefully.  The  temperature  at  which 
the  substitution  occurs  also  appears  to  determine  to  a  certain 
extent  the  relative  proportions  of  the  isomers  formed. 


INFLUENCE  OF  SUBSTITUENTS 


449 


The  substituted  benzole  acids  closely  resemble  benzoic  acid, 
and  yield  similar  derivatives.  The  strengths  of  the  different 
acids  largely  depend  upon  the  nature  of  the  substituents  and 
their  positions  with  respect  to  the  carboxylic  group. 


Acid.  M.-p.              K. 

Benzoiq 121°  0*006 

o-Methyl-benzoic 105°  0*012 

w-Methyl-benzoic 110°  0*00514 

p-Methyl-benzoic 180*  0'00515 

o-Bromo-benzoic 150°  0*145 

wi-Bromo-benzoic 155°  0*0137 

jo-Bromo-benzoic 251° 

o-Nitro-benzoic 148°  0*616 

m-Nitro-benzoic 141°  0*0345 

jp-Nitro-benzoic 240°  0*0396 

o- Ammo-benzole 145°  O'OOl 

Ttt-Ammo-benzoic 176°  0*003 

^- Ammo-benzole 186°  0*001 


Ethyl  ester. 
M.-p.  B.-p. 

211° 
220° 
225° 
228° 
254° 
259° 


30° 
47° 
57° 
13° 

89° 


267° 
294° 


The  numbers  for  K  given  in  the  table  indicate  that  the 
introduction  of  negative  radicals,  e.g.  N02,  Br,  &c.,  more 
especially  into  the  ortho-position,  markedly  increases  the 
strength  of  the  acid,  whereas  the  introduction  of  positive 
radicals,  e.g.  the  amino-,  more  especially  into  ortho-positions, 
tends  to  weaken  the  acid  (cf.  p.  168). 

Chemical  Retardation  and  Influence  of  Substituents  (cf. 
p.  175).  —  Within  recent  years  a  number  of  examples  of  the 
retardation  or  complete  inhibition  of  chemical  reactions  by  the 
presence  of  ortho-substituents  have  been  discovered.  One  of 
the  best  known  examples  of  this  is  met  with  in  the  esterifi- 
cation  of  aromatic  acids  by  the  hydrogen  chloride  catalytic 
method.  Kellas  (Zeit.  Phys.  Chem.,  1897,  24,  221)  has  shown 
that  even  one  ortho-substituent,  whether  it  be  CH3,  N02,  Br, 
&c.,  retards  the  formation  of  ester;  and  V.  Meyer  and  Sudborough 
(B.  1894,  27,  510,  1580,  and  3146)  have  shown  that  when  two 
such  ortho-substituents  are  present  an  ester  is  not  formed 
at  all.*  The  cause  of  this  retardation  and  inhibition  is  now 
generally  supposed  to  be  due  to  the  fact  that  in  the  formation 
of  an  ester  an  additive  compound  of  the  acid  and  alcohol, 


+  CH3.OH  = 


+  HaO. 


*  Esters  of  such  acids  can  be  prepared  by  heating  the  acids  with  alcohol 
to  high  temperatures. 

(8480)  2? 


450  XXVI.   AROMATIC  ACIDS 

is  first  formed,  that  this  compound  then  decomposes  into  the 
ester  and  water,  and  that  the  spatial  arrangements  are  such 
that  ortho-substituents  are  so  close  to  the  carboxylic  group 
that  they  interfere  with  the  formation  of  an  additive  com- 
pound, and  thus  retard  or  inhibit  esterification  (Wegscheider). 
In  confirmation  of  this  view  we  have  the  fact  that  0-substituents 
do  not  interfere  to  nearly  the  same  extent  when  the  carboxylic 
group  is  removed  some  distance,  e.g.  by  the  interposition  of  a 
chain  of  carbon  atoms.  The  acid, 


_ 
Br/~    YCH2.CH2. 


s-tribromo-hydrocinnamic  acid,  for  example,  is  readily  esterified 
under  the  usual  conditions.  Other  cases  of  chemical  retarda- 
tion due  to  o-substituents  have  been  met  with  in  the  hydro- 
lysis of  substituted  benzo-nitriles;  compounds  like 

ON  CN 


cannot  be  hydrolysed  to  the  corresponding  acids  by  the  usual 
methods.  Di-ortho-substituted  benzoyl  chlorides  and  benz- 
amides  and  %  benzoic  esters  are  also  remarkably  stable  and 
difficult  to  hydrolyse  to  the  acids  (Sudborough,  Ira  Remsen). 
Di-ortho-substituted  ketones, 

COE 


CH 


cannot  be  converted  into  oximes  (F.   Meyer),  and  di-ortho- 
substituted  tertiary  amines, 

N(CH3)2 


cannot  yield  quaternary  ammonium  salts  (p.  379)  (E.  Fischer). 
That  ortho-substituents  do  not  retard  or  inhibit  all  chemical 
actions  is  shown  by  the  fact  that  esters  of  di-ortho-substituted 


INFLUENCE  OF  SUBSTITUENTS  451 

benzoic  acids  may  be  obtained  by  other  methods,  viz.  the 
action  of  the  alcohol  on  the  acid  chloride,  and  the  action  of 
alkyl  iodide  on  the  silver  salt  of  the  acid,  or  of  methyl  sul- 
phate on  an  alkali  salt  of  the  acid. 

In  certain  reactions  the  presence  of  ortho-substituents  ap- 
pears to  favour  or  accelerate  a  chemical  reaction;  examples  of 
this  are  to  be  met  with  in  the  diacetylation  of  arylamines 
(Sudb&rough,  J.  C.  S.  1901,  79,  533)  and  in  the  chemical  re- 
activity of  picryl  chloride, 


02 

and  similar  compounds.  The  reactivity  of  various  substituents, 
such  as  01,  NH2,  &c.,  which  are  in  the  o-  or  ^-position  with 
respect  to  a  nitro-group,  has  been  noted  previously  (pp.  362, 
374,  414).  A  simple  explanation  of  this  reactivity  may  be  due 
to  the  formation  of  an  o-  or  jp-quinonoid  additive  product. 
Thus  in  the  action  of  alkalis  on  0-nitraniline  : 


NH  . 

\/NH>  \/M>K2  \/°K 

where  the  NH2  group  is  replaced  by  OK,  an  ortho-quinonoid 
compound  may  be  formed  as  indicated  above,  and  this  by  the 
loss  of  ammonia  would  yield  the  potassic  derivative  of  0-nitro- 
phenol. 

The  amino-benzoic  acids,  NH2  •  C6H4  •  C02H,  which  are  ob- 
tained by  the  reduction  of  the  nitro-acids  with  tin  and  hydro- 
chloric acid,  &c.,  are  interesting,  as  they  are  both  bases  and 
acids,  i.e.  amphoteric,  and  therefore  similar  to  glycocoll  in 
chemical  character;  they  combine  with  hydrochloric  acid, 
chloro-platinic  acid,  &c.,  as  well  as  reacting  with  mineral 
bases  to  yield  metallic  salts.  With  regard  to  their  consti- 
tution, cf.  Glycocoll,  p.  212. 

With     nitrous    acid     they    yield     diazo-  benzoic    acids, 

C6H4<^QQ   /»,    which    correspond    with    the   diazo  -benzene- 

sulphonic  acids. 
0-Amino-benzoic  acid  is  also  obtained  from  phthalimide, 

by  the  Hofmann  reaction  (cf.  Amides,  b§ 


452  XXVI.   AROMATIC  ACIDS 

haviour  of,  par.  5),  and  by  the  oxidation  of  indigo  with  man- 
ganese dioxide  and  caustic  soda,  and  is  often  termed  anthra- 
nilic  acid;  it  forms  (in  contradistinction  to  the  m-  and  #-acids) 

r-\r\ 

an  intramolecular  anhydride,  anthranil,  C6H4<^jj^>,  and  is 

an  important  intermediate  product  in  the  synthesis  of  indigo. 
The  methyl  ester  is  an  important  constituent  of  the  essential 
oil  of  orange-blossom. 

The  sulpho-benzoic  acids,  OH  .  S02  .  C6H4  .  CO  .  OH,  are  di- 
basic acids.  An  ammonia  derivative  of  o-sulpho-benzoic  acid 

QO 

is  the  sweet  substance   "saccharine",  C6H4<^Q2^>NH,  i.e. 

0-sulpho-benzimide,  or  0-benzoyl-sulphone-imide,  an  imide  com- 
parable with  succinimide.  It  is  a  white  crystalline  powder, 
almost  three  hundred  times  as  sweet  as  cane-sugar,  and  is  used 
to  some  extent  in  place  of  the  latter. 

Acids,  C8H802.—  1.  The  three  toluic  acids,  CH3.C6H4.C02H, 
can  be  prepared  from  the  three  xylenes.  ^-Toluic  acid  is  ob- 
tained from  ^-toluidine,  by  transforming  it  —  according  to  the 
Sandmeyer  reaction  —  into  ^-cyano-toluene  and  hydrolysing  the 
latter  (A.  258,  9).  Isomeric  with  them  is  — 

2.  Phenyl  -  acetic  acid,  a  -Toluic  acid,  C6H5  •  CH2  •  C02H 
(Cannizaro,  1855).  —  This  acid  differs  characteristically  from  its 
isomers  by  its  behaviour  upon  oxidation  (see  p.  444).  It  may 
be  obtained  synthetically  from  benzyl  chloride  and  potassium 
cyanide,  benzyl  cyanide,  C6H5«CH2.CN  (b.-pt.  232°),  being 
formed  as  intermediate  product;  it  crystallizes  in  lustrous 
plates,  melts  at  76°,  and  boils  at  262°. 

It  is  capable  of  undergoing  substitution  either  in  the  benzene 
nucleus  or  in  the  side  chain.  In  the  latter  case  there  are 
formed  compounds  such  as  — 

Phenyl-chloracetic  acid,  CgH5«CHCl-C02H,  and  phenyl- 
amino-acetic  acid,  C6H5  •  CH(NH2)  •  C02H,  compounds  which 
possess  precisely  the  same  character  as  mono-chloracetic  and 
amino-acetic  acids.  Isomeric  with  phenyl-amino-acetic  acid  are 
the  three  amino-phenyl-acetic  acids,  NH2«C6H4»CH2«C02H, 
of  which  the  0-acid  is  interesting  on  account  of  its  close  relation 
to  the  indigo  group.  It  does  not  exist  in  the  free  state,  but 
forms  an  intramolecular  anhydride,  oxindole  (p.  522): 


Such  formation  of  an  intramolecular  anhydride  is  of  very 


HOMOLOGUES  OF  BENZOIO  ACID  453 

frequent  occurrence  in  ortho-amino-compounds  of  this  kind, 
in  contradistinction  to  the  m-  and  ^-compounds  (see  Indole). 
Theoretically,  it  may  take  place  in  the  above  instance  in  two 
different  ways,  viz.  either  by  the  elimination  of  a  hydrogen 
atom  of  the  ammo-group  together  with  OH  of  the  carboxyl,  or 
of  both  of  the  amino-hydrogen  atoms  with  the  oxygen  atom 
from  the  carbonyl  group.  These  two  cases  are  distinguished 
by  Baeyer  as  "  Lactam  formation  "  and  "  Lactim  formation  ". 
Oxindole  is  the  lactam  of  o-amino-phenylacetic  acid,  isatin, 

C6H4<^>>CO  (P-  523)>  tne  lactam  of  o-amino-phenylgly- 
oxylic  acid,  NH2.C6H4-CO.CO.OH,  and  carbostyril  (p.  456), 

/N=C»OH 

C6HX  •         ,  the  lactim  of  o-amino-cinnamic  acid. 

x/H :  CH 

Both  lactams  and  lactims  contain  hydrogen  which  is  readily 
replaceable;  in  the  former  case  it  is  present  in  the  amino- 
group,  and  in  the  latter  in  the  hydroxyl. 

If  the  compounds  which  result  from  the  replacement  of 
hydrogen  by  alkyl  are  very  stable,  the  alkyl  in  them  is 
linked  to  the  nitrogen,  and  they  are  derivatives  ol  the  lac- 
tams; if,  on  the  contrary,  they  are  easily  saponifiable,  the 
alkyl  is  linked  to  oxygen,  and  they  are  ethers  of  the  lactims. 
Many  lactams  and  lactims  react  as  tautomeric  substances  (cf. 
Isatin  and  chapter  on  Constitution  and  Physical  Properties). 

Acids,  C9H1002. — 1.  Dimethyl-benzole  acids,  Xylene-carloxylic 
acids,  C6IJ3Me2  •  C02H.  Of  these  six  are  possible,  and  four 
are  known.  Mesitylenic  acid,  (C02H : CH3 : CH3  =  1:3:5),  is 
prepared  by  the  oxidation  of  mesitylene.  Isomeric  with  them 
are — 

2.  The  Phenyl-propionic  acids. 

/3-Phenyl-propionic  acid  or  hydrocinnamic  acid,  CGH5  •  CH2  • 
CH2'C02H,  is  prepared  by  reducing  cinnamic  acid  with  sodium 
amalgam,  or  with  hydrogen  in  presence  of  colloidal  palladium, 
and  is  also  formed  during  the  decay  of  albuminous  matter.  It 
crystallizes  in  slender  needles;  m.-pt.  48°,  b.-pt.  280°. 

Many  substitution  products  of  this  acid  are  known,  among 
which  may  be  mentioned  o-nitro- cinnamic  acid  dibromide, 
N02.C6H4.CHBr.CHBr.C02H,  a  compound  nearly  related 
to  indigo  (p.  523);  further,  phenyl-a-amino-propionic  acid 
(phenyl-alanine),  C0H5.CH2.CH(NH2).C02H,  and  phenyl-/?- 
amino-propionic  acid,  C6H5.CH(NH2).CH2.C02H,  both  of 
which  can  be  prepared  synthetically,  the  former  being  like- 


454  XXVT.   AROMATIC  ACIDS 

wise  produced  during  the  decay  of  albumen  and  during  the 
germination  of  Lupinus  luteus. 

o-Amino-hydrociniiainic   acid,  C6H4<^  H2  <  QQ  H,   is  not 

stable,  but  is  immediately  transformed  into  its  lactirn,  hydro- 

carbostyril,  C6H4<^  -         ,  a  quinoline  derivative. 

^CH2  •  CH2 

Hydratropic  acid,  a-Phenyl-propionic  acid,  CH3  •  CH(C6H5)  • 
C02H,  is  obtained — as  its  name  implies — by  the  addition  of 
hydrogen  to  atropic  acid.  It  is  liquid  and  volatile  with  steam. 

2.  MONOBASIC  UNSATURATED  ACIDS 

1.  Cinnamic  acid,  C6H5  •  CH :  CH .  C02H  (Trommsdorf,  1780), 
occurs  in  Peru  and  Tolu  balsams  and  also  in  storax,  and  may 
be  prepared  as  given  at  p.  441.  It  crystallizes  in  needles  or 
prisms,  dissolves  readily  in  hot  water,  melts  at  133°,  and  boils 
at  300°.  When  fused  with  potash,  it  is  split  up  into  benzoic 
and  acetic  acids;  it  also  yields  benzoic  acid  when  oxidized. 
It  yields  salts,  esters,  &c.j  also  additive  compounds,  with 
chlorine,  bromine,  hydrogen  chloride,  bromide,  iodide,  and 
also  with  hydrogen  and  hypochlorous  acid,  e.g.  cinnamic  acid 
dibromide  (/?-phenyl-a-/3-dibromo-propionic  acid),  C6H5'CHBr. 
CHBr-C02H.  Further,  the  hydrogen  in  the  benzene  nucleus 
may  be  replaced  by  Cl,  Br,  N02,  NH2,  &c. 

Cinnamic  acids. — According  to  the  ordinary  stereo-chemical 
theory  of  unsaturated  compounds,  two  cinnamic  acids  of  the 
formula  C6H5  •  CH :  CH  •  C02H  should  exist  (cf.  Maleic  and 
Fumaric  acids,  p.  243).  Two  have  been  known  for  some 
time,  viz.  storax-cinnamic  acid,  melting  at  134°,  and  a//o-cin- 
namic  acid,  melting  at  68°,  prepared  by  reducing  /?-brom-allo- 
cinnamic  acid  with  zinc  and  alcohol.  But,  in  addition  to  these, 
several  other  cinnamic  acids  have  been  described  (for  summary 
see  Erhnmeyer,  Biochem.  Zeitsch.  1911,  34,  306):  (a)  Lieber- 
mann's  iso-cinnamic  acid  (B.  1890,  23,  141,  512),  melting  at 
5S°-59°;  this  occurs  naturally  together  with  the  allo  acid  in 
cocaine  alkaloids,  and  may  also  be  obtained  by  fractionally 
crystallizing  the  brucine  salt  of  allo-cinnamic  acid  (B.  1905, 
38,  2562),  and  decomposing  with  acid,  or  by  the  action  of  an 
alcoholic  solution  of  zinc  bromide  on  allo-cinnamic  acid  (B. 
1905,  38,  837).  (b)  Erlenmeyer's  iso-cinnamic  acid,  melting  at 
37°-38°,  and  obtained  by  reducing  a-brom-allo-cinriamic  acid 
with  zinc  and  alcohol  (A.  1895,  287,  1;  B.  1904,  37,  3361) 


CINNAMIC  ACIDS  455 

(c)  Triclinic  cinnamic  acid,  melting  at  80°.  (d)  Hetero-cin- 
namic  acid,  rn.-pt.  131°.  The  synthetical  acid  prepared  by 
Perkin's  method  is,  according  to  Erlenmeyer  (Abs.  1911,  i,  782), 
a  mixture  of  storax-  and  hetero-acids,  and  can  be  separated  by 
fractional  precipitation  of  the  sodium  salt  by  hydrochloric 
acid  or  by  fractional  distillation  of  the  ethyl  ester.  It  is 
probable  that  the  allo-  and  two  eso-acids  are  trimorphous  forms 
of  the  same  substance  (Biilmann,  B.  42,  182,  1443).  They 
appear  to  give  the  same  melt  as  shown  by  examination  of 
refractive  indices  (Stobbe),  and  solubilities  (Meyer),  and  also  to 
give  the  same  solutions  as  shown  by  their  electrical  conduc- 
tivities (Bjerum,  B.  43,  571),  and  absorption  spectra  (Stobbe, 
ibid.,  504).  Any  one  of  the  three  acids  can  be  obtained  from 
the  melt  by  impregnating  under  suitable  conditions  with  a 
crystal  of  the  desired  form;  and  even  the  solids  are  mutu- 
ally transformable  (Stobbe,  B.  44,  2735;  Meyer,  2966). 

According  to  Eiiber  and  Godschmidt  (B.  43,  453)  the  hetero- 
acid  is  an  impure  form  of  the  storax-acid,  but  this  is  denied 
by  Erlenmeyer  (Abs.  1911,  i,  782),  who  also  claims  to  have 
prepared  optically  active  cinnamic  acids  (ibid.,  781),  the  mole- 
cules of  which  must  be  asymmetric.  No  satisfactory  explana- 
tion of  the  existence  of  so  many  isomerides  has  been  offered 
so  far. 

Although  some  six  cinnamic  acids  are  known,  only  two 
a-bromo-cinnamic  acids  and  two  /?-bromo-cinnamic  acids  have 
been  prepared.  The  a-bromo-  and  a-brom-allo-cinnamic  acids 
are  obtained  by  the  elimination  of  hydrogen  bromide  from 
cinnamic  acid  dibromide: 

C6H6  •  CHBr  •  CHBr  •  C02H  -  HBr  =  C6H6  •  CH :  CBr  •  CO2H, 

or  its  esters,  and  they  melt  respectively  at  131°  and  120°. 
The  corresponding  /3-acids  can  be  prepared  by  the  addition  of 
hydrogen  bromide  to  phenyl-propiolic  acid: 

CfiHjj.C-C.COaH  +  HBr  =  CflH6.CBr:CH.CO2H. 

.They  melt  respectively  at  135°  and  159°.  (Compare  Sudborough 
and  Thompson,  J.  C.  S.  1903,  666,  1153;  Sudborough  and  Lloyd, 
ibid.,  1898,  91;  Sudborough  and  Roberts,  ibid.,  1905,  1841;  Sud- 
borough and  James,  ibid.,  1906,  105;  James,  1911,  1620. 
o-  and  _p-Nitro-cinnamic  acids,  NOg-CgH^CHzCH 
the  first  of  which  is  of  importance  on  account  of  its  relation 
to  indigo,  are  obtained  by  the  nitration  of  cinnamic  acid. 


456  XXVI.   AROMATIC  ACIDS 

On  reduction  the  former  yields  o-amino-cinnamic  acid,  which 
readily  yields  its  lactim  carbostyril  (a-hydroxy-quinoline), 
")H:CH 


=C.OH 

The  radical  of  cinnamic  acid,  i.e.  (C6H6  •  CH :  CH  •  CO— ), 
is  termed  "  cinnamyl ",  and  the  group  (C6H5  •  CH :  CH — ) 
"  cinnamenyl". 

2.  Atropic   acid,  CH2 :  C(C6H5)  •  C02H,  is  a  decomposition 
product  of  atropine.     It  crystallizes  in  monoclinic  plates,  and 
can  be  distilled  with  steam.      It  breaks  up  into  formic  and 
a-toluic  acids  when  fused  with  potash. 

3.  (y)-Phenyl-isocrotonic  acid,  C6H5 .  CH :  CH .  CH2 .  C02H,  is 
formed  when  benzaldehyde  is  heated  with  sodium  succinate  and 
acetic  anhydride  (W.  H.  Perkin,  sen.,  also  Jayne,  A.  216,  100): 

C6H6-CHO  -f  CH2(CO2H).CH2.CO2H  -  H2O 
•  Oxi  •  UJjL^vA^.tly  •  ^-ti2 

6 co 


=  CO2  +  C6H5.CH:CH.CH2.CO2H. 

It  is  of  interest  on  account  of  its  conversion  into  a-naphthol 
(see  this),  C10H7»OH,  upon  boiling. 

4.  Phenyl-propiolic  acid,  C6H5.C:C.C02H  (Glaser,  1870), 
is  prepared  from  cinnamic  acid  dibromide  or  its  ethyl  ester  by 
first  converting  into  a-brom-cinnamic  acid  by  elimination  of 
hydrogen  bromide,  and  then  into  the  acetylenic  acid  by 
further  elimination  (just  as  ethylene  is  converted  by  bromine 
into  ethylene  bromide,  and  the  latter  decomposed  into  acety- 
lene by  potash).  It  crystallizes  in  long  needles,  and  melts  at 
136°-137°.  When  heated  with  water  to  120°,  it  breaks  up 
into  C02  and  phenyl-acetylene  (p.  353).  It  can  be  reduced  to 
hydrocinnamic  acid  and  transformed  into  benzoyl-acetic  acid. 

0-Nitro-phenyl-propiolic  acid,  N02  •  C6H4  •  C  •  C  •  C02H 
(Baeyer),  is  prepared  in  a  manner  analogous  to  that  just  given, 
viz.  by  the  addition  of  bromine  to  ethyl  0-nitro-cinnamate  and 
treatment  of  the  resulting  bromide  with  alcoholic  potash  (A. 
212,  240).  It  is  of  interest  on  account  of  its  relation  to  indigo 
(see  p.  626).  It  breaks  up  into  C02  and  0-nitro-phenyl-acety- 
lene  when  heated. 

3.  SATURATED  PHENOLIC  ACIDS 

(For  modes  of  formation,  see  p.  440.)  These  acids  may  also 
be  obtained  by  the  oxidation  of  the  homologues  of  phenol 


PHENOLIC  ACICS  467 

and  of  the  hydroxy-aldehydes,  which  is  effected,  among  other 
methods,  by  fusion  with  alkalis. 

The  phenolic  acids  form  salts  both  as  carboxylic  acids  and  as 
phenols,  salicylic  acid,  for  instance,  the  two  following  classes : 

)H 


and 

Mono-  and    Di-sodium  salicylate. 

The  first  of  these  two  salts  is  not  decomposed  by  C02,  while 
the  second,  as  the  salt  of  a  phenol,  is  decomposed  by  it  and 
converted  into  the  first.  The  phenolic  acids  behave,  therefore, 
like  monobasic  acids  towards  sodium  carbonate.  When  both 
of  the  hydrogen  atoms  are  replaced  by  alkyl,  there  are  formed 
compounds  such  as  C2H50  •  CJH4  •  C02C2H6,  which,  as  both 
ethers  and  esters,  are  only  half  hydrolysed  when  boiled  with 
potash,  e.g.  to  C2H50  •  C6H4  •  C02H,  ethyl  salicylic  acid.  The 
ether  acids  thus  formed  possess  completely  the  character  of 
monobasic  acids,  their  alphyl  radical  being  only  eliminated  by 
hydriodic  acid  at  a  rather  high  temperature.  (Cf.  p.  412.) 

The  0-hydroxy-acids  (C02H:OH  =1:2)  are,  in  contradis- 
tinction to  their  isomers,  volatile  with  steam,  give  a  violet  or 
bhie  coloration  with  ferric  chloride,  and  are  readily  soluble  in 
cold  chloroform. 

The  m-hydroxy-acids  are  more  stable  than  the  o-  and  ^-com- 
pounds; while  most  of  the  latter  break  up  into  carbon  dioxide 
and  phenols  when  quickly  heated,  or  when  acted  on  by  hydro- 
T  chloric  acid  at  220°,  the  former  remain  unaltered. 

The  phenolic  acids  are  much  more  easily  converted  into 
halogen  or  nitro-substitution  products   than   the   monobasic 
acids,  just  as  the  phenols  are  far  more  readily  attacked  than 
\the  benzene  hydrocarbons. 

v  Salicylic  acid,  o-Hydroxy-lenzoic  add  (C02H:OH  =  1:2), 
was  discovered  by  Piria  in  1839.  It  occurs  in  the  blossom  of 
Spiraea  Ulmaria,  and  as  its  methyl  ester  in  oil  of  winter-green, 
&c.  It  may  be  obtained  by  the  oxidation  of  the  glucoside 
saligenin;  by  fusing  coumarin,  indigo,  0-cresol,  &c.,  with  potash; 
by  diazotizing  o-amino-benzoic  acid,  &c.  (see  p.  387). 

Preparation. — Sodium  phenoxide  is  heated  in  a  stream  of 
carbon  dioxide  at  180°-220°  (Kolbe,  A.  113,  125;  115,  201,  &c.), 
when  half  of  the  phenol  distils  over  and  basic  salicylate  of 
sodium  remains  behind: 

C6H6  •  ONa  +  CO2  =  OH  •  C6H4  •  CO  JSTa ; 

2Na  +  C6H6.ONa  =  ONa.C6H4.(X)2Na -f  C6H6-OH. 


4:58  XXVI.   AROMATIC  ACIDS 

Should  potassic  phenoxide  be  used  instead  of  the  sodic  com- 
pound, salicylic  acid  is  likewise  formed  if  the  temperature  be 
kept  low  (150°),  but  the  isomeric  para-hydroxy-benzoic  acid 
at  a  higher  temperature  (220°).  Mono-potassic  salicylate, 
C6H4(OH)  •  C02K,  decomposes  in  an  analogous  manner  at  220° 
into  phenol  and  di-potassic  ^-hydroxy-benzoate. 

As  Kolbe's  original  method  of  preparation  converted  only 
50  per  cent  of  the  phenol  into  salicylic  acid,  Schmitt  devised 
the  following  modification:  —  The  sodic  phenoxide  is  heated  in 
a  closed  vessel  with  carbon  dioxide  at  130°,  and  the  compound 

first  formed,  C6H5'0»C<^Q    a,  sodic  phenyl-carbonate,  is  thus 

transformed  into  mono-sodic  salicylate  by  the  exchange  of  the 
•  CO  •  ONa  group  with  the  ortho-hydrogen  atom  of  the  phenyl 
radical.  (Cf.  B.I  905,  38,  1375;  A.  1907,351,313;C.C.1907,ii,48.) 
Salicylic  acid  crystallizes  in  colourless  four-sided  monoclinic 
prisms,  dissolves  sparingly  in  cold  water  but  readily  in  hot; 
it  melts  at  155°,  can  be  sublimed,  but  is  decomposed  into 
phenol  and  C02  when  heated  quickly;  ferric  chloride  colours 
the  aqueous  solution  violet.  It  is  an  important  antiseptic. 
It  forms  two  series  of  salts  (the  basic  calcium  salt  being 
insoluble  in  water),  and  two  series  of  derivatives,  viz.:  (1)  as 
an  acid  it  yields  chlorides,  esters,  &c.,  and  (2)  as  a  phenol  it 
yields  ethers,  &c.,  e.g.  ethyl-salicylic  acid,  C6H4(0  •  C2H5)C02H. 


Phenyl  salicylate,  CWKco-OC  ^  ,  the  ester  derived  from 

phenol  and  salicylic  acid,  and  generally  termed  "Salol",  is 
a  good  antiseptic,  and  is  prepared  by  the  action  of  an  acid 
chloride  such  as  POC13  or  COC12  upon  a  mixture  of  salicylic 
acid  and  phenol,  or  by  heating  the  acid  itself  at  220°.  It 
forms  colourless  crystals.  When  its  sodium  salt  is  heated  to 
300°,  it  undergoes  molecular  transformation  into  the  sodium 
salt  of  the  isomeric  phenyl-salicylic  acid,  C6H5O.C6H4-C02Na 
(B.  21,  501).  Analogous  "salols"  are  obtained  from  <;ther 
phenols,  e.g.  j?-acetylaminophenol  yields  salophene. 

m-Hydroxy-benzoic  acid  is  prepared  by  diazotizing  w-amino- 
benzoic  acid.  It  crystallizes  in  microscopic  plates,  dissolves 
readily  in  hot  water,  and  sublimes  without  decomposition; 
ferric  chloride  does  not  colour  its  aqueous  solution. 

^-Hydroxy-benzoic  acid  forms  monoclinic  prisms  (-f-  H20), 
and  ferric  chloride  gives  no  coloration  with  the  aqueous 
solution.  As  a  phenol  it  yields  the  methyl  ether,  anisic 


ttYDROXY-ACIDS  469 

acid,  C6H4(0  •  CH3)  •  C02H,  which  can  be  prepared  by  treat- 
ing ^-hydroxy-benzoic  acid  with  methyl  alcohol,  potash  and 
methyl  iodide,  and  saponifying  the  dimethyl  derivative  first 
formed;  it  is  also  formed  by  the  oxidation  of  anisole.  In 
consequence  of  the  phenolic  hydroxyl  having  been  etherified, 
it  resembles  the  monobasic  and  not  the  phenolic  acids,  boiling 
— for  example — without  decomposition;  hydriodic  and  hydro- 
chloric acids  at  high  temperatures  decompose  it  into  j?-hy- 
droxy-benzoic  acid  and  methyl  iodide  or  chloride. 

Hydro-para-coumaric  acid  (1 : 4),  OH  •  C6H4  •  CH2  •  CH2  •  C0.2H, 
^-p-hydroxy-plienyl-propionic  add,  is  produced  by  the  de 


lecay  of 

tyrosine,  fi-hydroxy-phenyl-alanine,  OH  •  C6H4  •  CH2  •  CH(NH2)  • 
C02H,  and  also  synthetically  from  jo-nitro-cinnamic  acid  : 

NO2.C6H4.CH:CH.CO2H    —    NH2.C6H4.CH2.CH2.CO2H 

reduced 

—  OH.C6H4.CH2.CH2.C02H 

diazotized 

Tyrosine,  which  crystallizes  in  fine  silky  needles,  is  found  in 
old  cheese  (TU/>OS),  in  the  pancreatic  gland,  in  diseased  liver, 
in  molasses,  &c.,  and  results  from  albumen,  horn,  &c.,  either 
upon  boiling  these  with  sulphuric  acid  or  from  their  pancreatic 
digestion  or  their  decay. 

It  has  also  been  obtained  synthetically,  as  indicated  by  the 
following  series  of  reactions:  — 


C6H6.CH2.CHO 

—  C6H6  •  CH2  •  CH(OH)  .  ON  -f  NH, 
—  C6H6.CH2.CH(NH9).CN 

-*  C6H5.CH2.CH(NH,)-CO2H 

—  NO2-C6H4.CH2.CH(NH2).CO2H 

—  OH.C6H4.CH2.CH(NH2).CO2H. 

(Compare  also  B.  32,  3638.) 

Of  the  numerous  polyhydroxy-phenolic  acids,  the  following 
may  be  mentioned  :  — 

Protocatechuic  acid,  3'A-Dihydroxy-benzoic  acid,  is  obtained 
by  fusing  various  resins,  such  as  catechu,  benzoin,  and  kino, 
with  alkali.  It  may  be  prepared  synthetically,  together  with 
the  2  :  3-dihydroxy-acid,  by  heating  catechol,  C6H4(OH)2,  with 
ammonium  carbonate.  It  crystallizes  in  glistening  needles  or 
plates,  and  is  readily  soluble  in  water;  the  solution  is  coloured 
green  by  ferric  chloride,  then  —  after  the  addition  of  a  very  little 
sodic  carbonate  —  blue,  and  finally  red.  Like  catechol  it  pos- 
sesses reducing  properties.  Its  mono-methyl  ether  is  vanillic 


460  X!XVi.   AltOMATiC  ACtt)S 

acid,  or  p-hydroxy-nwnethoxy-benzoic  acid,  C6H3(C02H)(0  •  CH3) 
(OH),  which  is  obtained  by  the  oxidation  of  vanillin  (p.  430); 
its  dimethyl  ether  is  the  veratric  acid  of  sabadilla  seed  (Ver- 
atrum  Sabadilla),  and  its  methylene  ether  is  piperonylic  acid, 

CH2<^Q^>C6H3«C02H,  which  can  be  prepared,  among  other 

methods,  by  the  oxidation  of  piperic  acid  (p.  464). 

Gallic  acid,  3 -A \5-Trihydroxy-benzoic  acid,  C6H2(OH)3C02H, 
occurs  in  nut-galls,  in  tea  and  many  other  plants,  and  as  gluco- 
sides  in  several  tannins.  It  is  prepared  by  boiling  tannin  with 
dilute  acids,  or  by  allowing  mould  to  form  on  its  solution,  and 
has  also  been  obtained  synthetically  by  various  reactions.  It 
crystallizes  in  fine  silky  needles  (+  H20),  dissolves  readily  in 
water,  alcohol,  and  ether,  and  has  a  faintly  acid  and  astringent 
taste.  It  evolves  carbon  dioxide  readily  when  heated,  yield- 
ing pyrogallol,  reduces  gold  and  silver  salts,  and  yields  a 
bluish-black  precipitate  with  ferric  chloride.  Like  pyrogallol, 
it  is  very  readily  oxidized  in  alkaline  solution,  with  the  pro- 
duction of  a  brown  colour. 

Gallic  acid  is  used  in  the  manufacture  of  blue-black  inks. 
With  ferrous  sulphate  it  gives  a  pale -brown  colour,  which 
rapidly  turns  black  on  exposure  to  the  air;  the  presence  of 
a  minute  quantity  of  free  sulphuric  acid  retards  this  oxida- 
tion, but  when  the  acidified  solution  is  used  with  ordinary 
paper  the  acid  is  neutralized  by  compounds  present  in  the 
paper,  and  the  oxidation  takes  place.  Indigo  carmine  is  added 
to  the  ink  in  order  to  give  it  a  blue  colour  before  oxidation 
occurs.  Dermatol  and  Airol  are  bismuth  derivatives. 

Tannin,  Gallotanic  add,  is  a  colourless,  amorphous,  glistening 
mass,  readily  soluble  in  water  but  only  slightly  in  alcohol, 
and  almost  insoluble  in  ether.  It  forms  the  chief  constituent 
of  nut-galls,  and  is  likewise  present  in  sumach,  tea,  &c.  It 
yields  gallic  acid  when  boiled  with  dilute  acids,  and  a  product 
similar  to  tannin  may  be  obtained  from  gallic  acid  by  the  de- 
hydrating action  of  phosphorus  oxychloride.  The  constitution 
is  not  known ;  it  is  evidently  a  complex  compound,  and  appears 
to  be  optically  active. 

The  aqueous  solution  is  coloured  dark-blue  by  ferric  chloride. 
The  mercury  salt  is  used  in  medicine.  Tannin  has  an  affinity 
for  the  animal  skin  and  for  glue,  and  is  abstracted  from  its 
solution  by  these  substances,  the  skin  being  thus  tanned  or 
converted  into  leather.  Numerous  other  tannic  acids  are 
known,  and  are  usually  named  according  to  the  plant  from 


ALCOHOL-ACIDS  461 

which  they  are  obtained,  e.g.  kino  tannin,  catechu  tannin, 
coffee  tannin,  &c. 

Quinic  acid,  which  is  found  in  quinine  bark,  coffee  beans,  &c., 
is  a  hexahydro-tetrahydroxy-benzoic  acid,  C6H7(OH)4C02H. 
It  crystallizes  in  colourless  prisms  and  is  optically  active,  an 
inactive  modification  being  also  known. 

4.  ALCOHOL-  AND  KETO-ACID3 

The  monobasic  aromatic  alcohol-acids,  which  possess  at  one 
and  the  same  time  the  characters  of  acids  and  of  true  alcohols 
(p.  436),  contain  the  alcoholic  hydroxyl  in  the  side  chain;  this 
hydroxyl  is  consequently  eliminated  together  with  the  side 
chain  when  the  compound  is  oxidized. 

In  behaviour  they  approximate  very  closely  to  the  hydroxy- 
acids  of  the  fatty  series,  as  the  phenylated  derivatives  of  which 
they  thus  appear;  at  the  same  time  they  yield,  as  phenyl  de- 
rivatives, nitro-compounds,  &c.,  although  those  compounds  can 
often  not  be  prepared  directly,  on  account  of  the  readiness 
with  which  the  acids  are  oxidized.  They  differ  from  the 
phenolic  acids  in  being  more  soluble  in  water,  less  stable,  and 
non-volatile;  as  alcohols  many  of  them  give  up  water  and 
yield  unsaturated  acids  (which  the  phenolic  acids  can  never 
do),  and  they  can  be  esterified  by  hydrobromic  acid,  &c.,  with 
the  formation  of  haloid-substitution  acids,  &c.  Further,  they 
are  purely  monobasic  acids. 

The  hydroxy-acids  may  be  either  primary,  secondary,  or 
tertiary  alcohols,  e.g.  OH . CH2 . C6H4 . COOH,  C6H5.CH(OH). 
COOH,  and  C6H5 .  CH2 .  C(CH3)(OH) .  COOH.  The  tertiary 
can  sometimes  be  prepared  directly  by  the  oxidation  of  such 
acids  CnH2n_802  as  contain  a  tertiary  hydrogen  atom  (:CH), 
by  means  of  permanganate. 

To  the  ketonic  acids  the  corresponding  reactions  apply.  As 
ketones  they  may  be  reduced  to  secondary  alcohol-acids,  and 
they  further  react  with  hydroxylamine,  &c.;  as  acids  they  form 
salts,  esters,  &c. 

Mandelic  acid,  Phenyl-glycollic  acid,  C<.H5 .  CH(OH) .  C02H 
(1835),  is  formed  by  hydrolysing  amygdalin  with  hydrochloric 
acid,  and  synthetically  by  the  hydrolysis  of  benzaldehyde-cyan- 
hydrin,  C6H5 .  CH(OH)  •  ON  (see  pp.  126  and  424).  It  forms 
glistening  crystals,  dissolves  somewhat  readily  in  water,  and 
melts  at  133°. 

Mandelic  acid  possesses  an  asymmetric  carbon  atom  and 


462  XXVI.   AROMATIC  ACIDS 

exists  in  two  optically  active  modifications  (cf.  B.  16, 1565  and 
2721),  and  these  can  form  a  racemic  compound  (para-mandelic 
acid)  in  the  same  manner  as  d-  and  Z-tartaric  acids. 

The  acid  obtained  synthetically  is  the  racemic  acid,  but  this 
can  be  resolved  (1)  by  the  aid  of  chinchonine  when  the  chin- 
chonine  salt  of  the  d-acid  crystallizes  first;  (2)  by  means  of 
green  mould,  "  penicillium  glaucum  ",  which  when  grown  on  a 
solution  of  the  ammonium  salt  of  the  acid  destroys  the  Isevo 
modification;  (3)  by  partially  esterifying  the  racemic  acid  with 
an  optically  active  alcohol,  e.g.  Z-menthol;  the  non-esterified 
acid  is  then  /-rotatory,  as  the  d-acid  is  somewhat  more  readily 
esterified  by  /-menthol  than  the  Z-acid.  The  method  is  not 
quantitative  (Marckwald  and  Mackenzie,  B.  1899,  32,  2130; 
1901,  34,  469;  also  J.  C.  S.  1899,  964).  The  acid  obtained 
from  amygdalin  is  the  laevo  compound.  It  is  comparable  with 
lactic  acid,  CH3  •  CH(OH)  •  C02H,  yielding,  like  the  latter, 
formic  acid  (together  with  benzoic)  when  oxidized;  hydriodic 
acid  reduces  it  to  phenyl-acetic  acid,  just  as  it  does  lactic  acid 
to  propionic. 

o-Hydroxymethyl-benzoic  acid,  OH  •  CH2  •  CLH4  •  CO  •  OH, 
which  is  isomeric  with  mandelic  acid,  is  unstable  in  the  free 
state;  as  an  ortho-compound,  it  readily  yields  the  anhydride 

or  lactone,  Phthalide,  C6H4<\QQ2^>0,  which  is  obtained  by 

the  reduction  of  phthalic  anhydride  or  chloride.  It  crystallizes 
in  needles  or  plates,  and  can  be  sublimed  unaltered. 

Tropic  acid,  a- Phenyl-fi-hydroxy -propionic  add,  OH»CH2« 
CHPh«C02H  (fine  prisms),  is  obtained  together  with  tropine 
by  boiling  atropine  with  baryta  water;  it  is  reconverted  into 
atropine  when  warmed  with  tropine  and  hydrochloric  acid. 
It  exists  in  several  optically  different  (d-t  J-,  and  r-)  modifi- 
cations. 

Benzoyl-formic  acid,  Phenyl-glyoxylic  acid,  C6H5«CO«C02H, 
is  obtained  synthetically  by  the  hydrolysis  of  benzoyl  cyanide, 
CgHg-CO-CN,  with  cold  fuming  HC1  (Claisen,  1877),  and  also 
by  the  cautious  oxidation  of  mandelic  acid  or  acetophenone. 
It  is  an  oil  which  only  solidifies  slowly,  and  when  distilled 
is  largely  decomposed  into  carbon  monoxide  and  benzoic  acid. 
It  reacts  similarly  to  isatin  with  benzene  containing  thiophene 
and  sulphuric  acid,  and  shows  the  normal  reactions  of  the 
ketonic  acids  with  NaHS03,  HCN,  NH2-OH,  &c. 

o-Nitro-benzoyl-fonnic  acid,  N02»C6H4.CO-C02H,  which 
can  be  prepared  from  0-nitro-benzoyl  cyanide,  yields  o  amino- 


UNSATURATED  PHENOLIC  ACIDS  463 

benzoyl-formic  acid,  isatic  acid,  NH2'C6H4»CO-C02H  (a  white 
powder),  upon  reduction;  when  a  solution  of  the  latter  is 
warmed,  it  yields  its  intramolecular  anhydride  (lactam),  isatin, 

>co  <cf* 


Benzoyl-acetic  acid,  C6H5.CO-CH2.C02H  (JBaeyer),  is  a 
perfect  analogue  of  acetoacetic  acid,  and,  like  the  latter,  can 
be  used  for  the  most  various  syntheses.  It  is  obtained  as  its 
ethyl  ester  (which  is  soluble  in  cold  sodic  hydroxide  solution) 
by  dissolving  ethyl  phenyl-propiolate  in  concentrated  sulphuric 
acid  and  pouring  the  solution  into  water  (B.  16,  2128);  or, 
better,  by  the  action  of  sodium  ethoxide  upon  a  mixture  of 
ethyl  benzoate  and  acetate  (Claisen's  condensation,  p.  225) 
(B.  20,  651).  It  is  crystalline,  melts  at  103°,  and  readily  splits 
up  into  carbon  dioxide  and  acetophenone,  C6H5-CO'CH3;  the 
aqueous  solution  is  coloured  a  beautiful  violet  by  ferric  chloride. 

5.   UNSATURATED  MONOBASIC  PHENOLIC  ACIDS 

Hydroxy-cinnamic  or  Coumaric  Acids,  OH»C6H4«CH:CH« 
COoH.  —  The  ortho-acid  is  present  in  melilot  (Melilotus  offidnalis), 
and  can  be  prepared  by  diazotizing  o-amino-cinnamic  acid,  or 
from  salicylic  aldehyde  by  Perkiris  synthesis.  The  alcoholic 
solution  is  yellow  with  a  green  fluorescence. 

yO  —  CO 

Coumarin,  C6H4<^         •     ,  is  the  aromatic  principle  of  wood- 

M-/H  i  CH 

ruff  (Asperula  odorata)^  and  is  also  found  in  the  Tonka  bean 
and  other  plants.  It  is  obtained  by  the  elimination  of  water 
from  0-coumaric  acid  by  means  of  acetic  anhydride.  It  crys- 
tallizes in  prisms,  dissolves  readily  in  alcohol,  ether,  and  hot 
water;  melts  at  67°,  and  boils  at  290°.  It  dissolves  in  sodium 
hydroxide  solution,  yielding  the  sodium  salt  of  couniarinic 
acid.  This  salt  is  stereo-isomeric  with  that  of  0-coumaric  acid. 
The  free  acid  itself  appears  to  be  incapable  of  existence,  as  it 
is  immediately  converted  into  coumarin  (its  anhydride),  but 
various  derivatives  are  known.  o-Coumarinic  acid  is  regarded 
as  the  cis-compound,  as  it  yields  an  anhydride  (cf.  Maleic  Acid). 
The  stereo-isomeric  o-coumaric  acid  is  the  trans-&c,id  (cf.  Fu- 
maric  Acid): 

H-C.C6H4.OH  H.C.C6H4.:OH 

H.OOC-C-H  H  c-co  -6:H 

o-Couinaric  Coumarinic  acid, 


464  XXVI.   AROMATIC  ACIDS 

3 : 4-Dihydroxy-cinnamic  acid,  Cafeic  add,  (OH)2  •  C6H3  •  CH : 
CH»CO2H,  crystallizes  in  yellow  prisms,  and  is  obtained  from 
caffetannic  acid,  whose  mono-methyl  ether  is  ferulic  acid  (from 
asafoetida);  the  isomeric  umhellic  acid  or^?-hydroxy-0-coumaric 
acid  readily  changes  into  the  anhydride  corresponding  to  cou- 
marin,  viz.  umbelliferone,  C9H6C3;  this  last-named  compound 
is  present  in  varieties  of  Daphne. 

Related  to  the  above  is  piperic  acid: 

•  CH :  CH  •  CH :  CH  •  COaH, 

a  decomposition  product  of  piperine  (p.  540),  which  crystallizes 
in  long  needles. 

B.  Dibasic  Acids 

The  dibasic  acids  occupy  exactly  the  same  position  in  the 
aromatic  series  as  the  dibasic  acids  CnH2n_204  do  in  the  fatty. 
They  contain  two  carboxyl  groups;  these  may  both  be  in  the 
nucleus  or  in  the  side  chain  or  chains,  or  be  divided  between 
them.  They  yield  acid  salts  and  normal  salts,  and  similarly 
two  series  of  esters,  amides,  &c.  Dibasic  phenolic  acids  can 
of  course  occur  here  also. 

1.  Phthalic  acid,  Benzene-o-dicarloxylic  add,  C6H4(C02H)2 
(Laurent,  1836),  is  formed  when  any  o-di-derivative  of  benzene, 
which  contains  two  carbon  side  chains,  is  oxidized  by  HN03  or 
KMn04,  but  not  by  Cr03  (cf.  p.  438);  it  is  generally  formed  by 
the  oxidation  of  naphthalene  by  nitric  acid,  and  also  of  anthra- 
cene derivatives.  In  preparing  it  on  the  large  scale  the  naph- 
thalene is  first  converted  into  its  tetra-chlor-addition  product, 
CjpHgCl^  and  then  oxidized.  At  the  present  time  phthalic 
acid  is  prepared  on  the  commercial  scale  by  oxidizing  naph- 
thalene with  concentrated  sulphuric  acid  in  the  presence  of 
a  small  amount  of  mercury  or  mercuric  sulphate  at  220-300°. 
It  crystallizes  in  short  prisms  or  plates,  melts  at  213°,  and  is 
readily  soluble  in  water,  alcohol,  and  ether.  When  heated 
above  its  melting-point,  it  yields  the  anhydride.  When  heated 
with  lime,  it  yields  benzoic  acid  or  benzene  according  to  the 
relative  amounts  of  acid  and  lime  used.  Chromic  acid  dis- 
integrates it  completely,  while  sodium  amalgam  converts  it 
into  dihydro-,  tetrahydro-,  and  finally  hexahydro-phthalic  acid 
(see  below).  Its  barium  salt,  C6H4(C02)2Ba,  is  sparingly  soluble 
in  water.  K  =  0-121. 


PHTHALIO  ACIDS  465 

Phthalic  anhydride,  C6H4<^pQ^>0,  crystallizes  in  magnifi- 

cent long  prisms  which  can  be  sublimed;  it  melts  at  128°,  boils 
at  284°,  and  is  used  in  the  preparation  of  eosin  dyes  (see 
Fluorescein). 

Phthalimide,  C6H4<^QQ^>NH,  corresponds  with  succinimide 

in  many  respects.  It  is  obtained  by  passing  dry  ammonia  over 
heated  phthalic  anhydride,  and  readily  gives  rise  to  metallic 
derivatives.  The  potassium  salt  C6H4(CO)2NK,  obtained  by  the 
action  of  aqueous  caustic  potash  on  an  alcoholic  solution  of  the 
imide,  readily  reacts  with  alkyl  iodides,  yielding  alkylated 
phthalimides,  e.g.  C6H4(CO)2NC2H5,  and  when  these  are  hy- 
drolysed,  primary  amines,  free  from  secondary  and  tertiary, 
are  obtained,  e.g.  : 

C6H4:(CO)2:NC2H5  +  2H20  =  C6H4(CO2H)2  +  C2H6NH2 


(Gabriel,  B.  1887-1897).  Numerous  primary  amines,  including 
halogenated  bases,  which  are  difficult  to  prepare  by  other 
methods,  have  been  obtained  in  this  way.  E.  Fischer  (B.  1901, 
34,  455)  has  also  used  the  same  method  for  the  preparation  of 
the  complex  amine  ornithine, 

NH2.CH2.CH2.CH2.CH(NH2).C02H, 

a5-diamino-?i-  valeric  acid.  The  various  steps  are:  —  Potassium 
phthalimide  and  trimethylene  bromide  yield 

C6H4  :  (CO)2  :  N  •  CH2  •  CH2  •  CH2Br, 

and  this  on  condensation  with  ethyl  sodio-malonate  gives 
C6H4  :  (C0)2  :  N  •  CH2  •  CH2  •  CH2  •  CH(CO2Et)2  ; 

and  on  bromination  and  subsequent  hydrolysis  and  loss  of 
carbon  dioxide 

C6H4:(CO)2:N.CH2.CH2.CH2.CHBr.C02H 

is  obtained.  Aqueous  ammonia  converts  this  into  the  corre- 
sponding amino-compound,  and  subsequent  hydrolysis  gives 
ornithine. 

The  chloride,  phthalyl  chloride,  which  is  obtained  by  the 
action  of  PCL  upon  the  acid  or  the  anhydride,  appears  not  to 

C^C^~\ 

have  the  normal  constitution  C6H4(COC1)2,  but  C6H4 


as  it  yields  phthalo-phenone,  C6H4<>0,  with  benzene 

(B480)  2G 


466  XXVI.   AROMATIC  ACIDS 

and  aluminium  chloride,  and  on  reduction  with  sodium  amal- 

PTT 
gam  it  yields  phthalide,  C6H4<^pQ2^>0,  the  constitution  of 

which  is  confirmed  by  its  conversion  on  hydrolysis  into  0-hy- 
droxy-methyl-benzoic  acid  (p.  462),  OH .  CH2 .  C6H4  •  CO  •  OH. 

2.  Isophthalic  acid  (1:3),  prepared  from  m-xylene,  crystal- 
lizes in  slender  needles  from  hot  water,  in  which  it  is  only 
sparingly  soluble;  it  sublimes  without  forming  an  anhydride. 
The  barium  salt  is  readily  soluble  in  water.     K  =  0'0287. 

Tlvitic  acid  is  5-methyl-isophthalic  acid,  and  may  be  obtained 
by  oxidizing  mesitylene. 

3.  Terephthalic  acid  (1:4)  is  obtained  by  the  oxidation  of 
jp-xylene,  cymene,  &c.,  and  especially  of  oil  of  turpentine  or  oil 
of  cumin.     It  forms  a  powder  almost  insoluble  in  alcohol  and 
water,  and  sublimes  unchanged.     For  its  preparation  jp-toluic 
acid  is  oxidized  by  potassic  permanganate  (A.  258,  9).     The 
barium  salt  is  only  sparingly  soluble. 

A.  Baeyer's  researches  (A.  245,  251,  258,  266,  269,  and  276) 
have  introduced  us  to  a  whole  series  of  reduction  products  of 
phthalic  acid,  generally  known  as  hydro-phthalic  acids.  The 
isomers  among  them  differ  from  one  another  either  by  the 
position  of  the  double  bond  in  the  ring  (structural  isomerism}, 
or  by  the  spatial  arrangement  of  the  carboxyl  groups  with 
respect  to  the  ring  (stereo-isomerism).  This  latter  isomerism 
corresponds  to  a  certain  extent  with  that  of  fumaric  and 
maleic  acids,  but  more  closely  with  that  of  the  poly-methylene 
compounds  (p.  325),  and  a  distinction  is  therefore  made  here 
also  between  a  trans-  and  a  as-form  (cf.  A.  245,  130).  Exactly 
the  same  applies  to  the  hydro-terephthalic  acids. 

Of  the  hydro-phtlialic  acids  (A.  269,  147)  there  are  now 
known : — Five  dihydro-acids  (two  of  which  are  stereo-isomeric), 
four  tetrahydro-acids  (of  which  two  again  are  stereo-isomeric), 
and  two  hexahydro-adds  (which  are  stereo-isomers).  Of  the 
hydro-terephthalic  acids  (A.  258,  1),  five  dihydro-,  three  tetra- 
hydro-,  and  two  hexahydro-acids  are  known,  two  in  each  group 
being  stereo-isomeric. 

The  following  principles  have  largely  served  for  determin- 
ing the  position  of  the  double  bonds  in  these  compounds: — 
(1)  When  bromine  substitutes  in  a  carboxylic  acid  it  takes  up 
the  a-position  to  the  carboxyl  (i.e.  it  is  attached  in  the  benzene 
nucleus  to  the  same  carbon  atom  to  which  the  carboxyl  is 
linked).  (2)  If  two  bromine  atoms  stand  in  the  ortho-position 
to  one  another  in  a  reduced  benzene  nucleus,  they  are  elimi- 


HYDRO-PHTHALIC  ACIDS  467 

nated,  without  replacement,  by  the  action  of  zinc  dust  and 
glacial  acetic  acid  ;  whereas,  if  they  stand  in  the  ^ra-positiori, 
they  are  replaced  by  hydrogen.  (3)  As  in  the  case  of  the  ali- 
phatic unsaturated  acids,  boiling  with  sodic  hydroxide  solution 
often  gives  rise  to  an  isomeric  acid,  due  to  the  "  wandering  " 
of  a  double  bond  in  the  direction  of  a  carboxyl  group  (p.  162). 
(4)  The  stereo-isomeric  modifications  are  also  easily  transformed 
one  into  the  other. 

The  relations  existing  between  the  five  known  dihydro- 
phthalic  acids  may  be  taken  as  an  example.  When  phthalic 
acid  is  reduced  by  sodium  amalgam  in  presence  of  acetic  acid, 
tois-A-3  :  5-dihydro-phthalic  acid  is  produced,  and  this  changes 
into  the  ces-A-3  :  5-acid  when  heated  with  acetic  anhydride  : 


Both  of  these  yield  the  A-2  :  6-dihydro-acid  when  warmed  with 
alkali.  When  the  dihydrobromide  of  the  latter  acid  is  treated 
with  alcoholic  potash,  the  A-2:4-dihydro-acid  results,  and,  lastly, 
the  anhydride  of  this  yields  the  anhydride  of  the  A-l  :  4-dihydro- 
acid  when  heated: 

H  H  H 


A-2:6  A-2:4  A-l:4 

All  the  dihydro-phthalic  acids  give  anhydrides  with  the  ex- 
ception of  the  tois-A-3  :  5-acid,  which  in  this  respect  comports 
itself  like  fumaric  acid. 

The  following  relationships  have  been  established  between 
the  hydro-terephthalic  acids:  — 

Terephthalic  acid  reduced  with  pure  sodium  amalgam  in 
faintly  alkaline  solution  gives  a  mixture  of  cis-  and  tois-A-2:5- 
dihydro-acids,  both  of  which  on  oxidation  readily  yield  tere- 
phthalic  acid.  When  boiled  with  water  both  are  converted 
into  the  A-l:5-dihydro-acid,  and  when  boiled  with  caustic  soda 

*  In  these  formulae  X  =  C02H,  A  denotes  the  double  bond,  and  the 
numbers  refer  to  the  carbon  atoms  after  which  the  double  bonds  are 
placed.  A-3:5  indicates  two  double  bonds,  one  between  carbons  3  and  4, 
and  a  second  between  carbons  5  and  6. 


468 


XXVI.   AROMATIC  ACIDS 


solution  into  the  A-l :  4-dihydro-acid.  This  acid  is  the  most 
stable  of  the  dihydro-acids,  and  is  always  obtained  by  the 
reduction  of  terephthalic  acid  unless  great  care  is  taken  in  the 
reduction. 

When  reduced  with  sodium  amalgam  the  A-l:5-acid  is  con 
verted  into  a  mixture  of  cis-  and  ^Yms-A-2-tetrahydro-acid. 
Both  acids  readily  combine  with  bromine,  which  can  again 
be  removed  by  means  of  zinc  dust;  this  dibromide,  when 
warmed  with  alcoholic  potash,  gives  the  A-l:3-dihydro-acid, 
which  cannot  be  obtained  directly  by  the  reduction  of  tere- 
phthalic acid. 

The  A-1-tetrahydro-acid  may  be  obtained  by  warming  the 
A-2-acid  with  sodium  hydroxide  solution. 

The  A-l -acid  yields  a  mixture  of  two  stereo-isomeric  di- 
bromides  (cis  and  trans),  and  these  when  reduced  with  zinc 
dust  and  acetic  acid  yield  the  cis-  and  /nws-hexahydro-tere- 
phthalic  acid: 

X  X 

X  I  X  X 


—    II  "I  and  I  - 

^ 

H  ±  A-l:5 

Cis-  and  £nms-A-2:5-dihydro         • 

XH  X  XH 


:H 

Hexahydro 
cis  and  trans 


Hi 

XH 

A-2-tetrahydro 
cis  and  trans 


A-l:  3- 
dihydro. 


The  completely  hydrogenized  acids  show  great  differences 
from  the  partially  hydrogenized.  Thus,  hexahydro-terephthalic 
acid  is  exactly  similar  to  a  saturated  acid  of  the  fatty  series; 
cold  permanganate  of  potash  has  no  effect  upon  it,  while  bro- 
mine substitutes  (upon  warming). 

On  the  other  hand,  the  partially  hydrogenized  acids  comport 
themselves  precisely  like  the  unsaturated  acids  of  the  fatty 
series  with  an  open  chain.  They  are  very  readily  oxidized 
by  cold  permanganate,  and  take  up  bromine  or  hydrobromic 


HYDROXY-PHTHALIC  ACIDS  469 

acid  until  the  saturation  stage  of  the  hexa-methylene  ring  is 
reached.  All  of  the  hydro-acids  can  be  transformed  back  into 
phthalic  acid  (A.  1894,  280,  94). 

For  hydro-ispphthalic  acids,  see  W.  H.  Perkin,  Jun.,  and  S.S 
Pickles,  P.  1905,  75,  and  Baeyer  and  Filliger,  A.  1893,  276,  255. 
Two  stereo-isomeric  modifications  of  the  hexahydro-acid  are 
also  obtained  synthetically  from  derivatives  of  the  fatty  series 
(Perkin,  J.  C.  S.  1891,  798).  This  constitutes  a  further  proof 
that  the  hexahydro-benzene-carboxylic  acids  are  nothing  more 
than  hexa-methylene  derivatives. 

A  large  number  of  substitution  products  of  the  phthalic  acids 
are  known,  e.g.  chloro-  and  bromo-phthalic  acids  (which  are 
used  in  the  eosin  industry),  nitro-,  amino-,  hydroxy-  and  sulpho- 
phthalic  acids,  &c. 

HYDROXY-PHTHALIC  ACIDS 

2^5-Dihydroxy-terephthalic  acid,  quinol-p-dicarloxyUc  actd, 
C6H2(OH)2(C02H)2,  in  which  both  the  hydroxyls  and  the  car- 
boxy  Is  are  respectively  in  the  ^-position  to  one  another,  is 
obtained  as  its  ethyl  ester  by  the  action  of  bromine  upon 
succinylo-succinic  ester,  or  of  sodium  ethoxide  upon  dibromo- 
acetoacetic  ester.  The  free  acid  breaks  up  into  quinol  and 
carbon  dioxide  when  distilled,  and  is  converted  by  nascent 
hydrogen  into  succinylo-succinic  acid. 

Succinylo-succinic  acid,  p-dihydroxy-dihydro-tereplithalic  acid, 
C6H4(OH)2(C02H)2,  is  obtained  as  its  ethyl  ester  by  the  action 
of  sodium  upon  ethyl  succinate  (see  p.  342).  The  ethyl  ester 
crystallizes  in  triclinic  prisms  which  melt  at  126°,  and  dissolves 
in  alcohol  to  a  bright-blue  fluorescent  liquid  which  is  coloured 
cherry-red  by  ferric  chloride.  It  contains  two  replaceable  hy- 
drogen atoms,  being  analogous  to  acetoacetic  ester.  The  free 
acid,  on  losing  carbon  dioxide,  changes  into  tetrahydro-quinone 
or  p-diketo-hexamethylene. 

The  ester  may  be  represented  as  a  dihydroxylic  compound 
or  as  a  diketone: 

C.C02Et  CH.C02Et 

•OH 


°     xx 

•  CO2Et 

ana  reacts  as  a  tautomeric  substance  (cf.  Ethyl  Acetoacetate). 


470.  XXVI.   AROMATIC  ACIDS 

C.  Polybasie  Acids 

Benzene  s-tricarboxylic  acid  or  trimesic  acid,  CJH3(COOH;3, 
can  be  obtained  by  the  oxidation  of  mesitylene.  The  isomeric 
unsym.  acid  or  trimellitic  acid  is  obtained  by  the  oxidation  of 
colophonium,  and  the  adjacent  acid  or  heuiimellitic  acid  is 
obtained  by  oxidizing  naphthalene-l:8-dicarboxylic  acid. 

The  benzene  tetracarboxylic  acids,  C6H2(C02H)4,  prehnitic 
acid  [1:2:3:4],  mellophanic  acid  [1:2:3:5],  and  pyromellitic 
acid  [1:2:4:5],  are  obtained  by  heating  mellitic  acid  or  its 
hexahydro-derivatives. 

Mellitic  acid,  Cg(CO2H)6,  occurs  in  peat  as  aluminium  salt 
or  honey-stone,  C12A12012  +  18H20,  which  crystallizes  in 
octahedra,  and  is  also  formed  by  the  oxidation  of  lignite  or 
graphite  with  KMn04.  It  forms  fine  silky  needles  of  great 
stability,  can  neither  be  chlorinated,  nitrated,  nor  sulphonated, 
but  is  readily  reduced  by  sodium  amalgam  to  hydromellitic 
acid,  C6H6(C02H)6,  and  yields  benzene  when  distilled  with 
lime. 

As  regards  the  esterification  of  these  polybasic  acids,  it  has 
been  found  that  carboxylic  groups  which  have  other  carboxylic 
groups  in  two  ortho-positions  cannot  be  esterified  by  the  usual 
catalytic  process,  e.g.  on  esterification  by  the  Fischer -Speyer 
method,  hemimellitic  acid  and  prehnitic  acid  yield  dimethyl 
esters  only,  pyromellitic  acid  yields  a  tetramethyl  ester,  and 
mellitic  acid  is  not  acted  on  (V.  Meyer  and  Sudborouqh.  B.  1894. 
27,  3146). 


XXVII.  AROMATIC  COMPOUNDS  CONTAIN- 
ING TWO  OR  MORE  BENZENE  NUCLEI. 
DIPHENYL  GROUP 

The  aromatic  compounds  hitherto  considered,  with  the  ex- 
ception of  azobenzene,  benzophenone,  &c.,  contain  but  one 
benzene  nucleus.  In  addition  to  these,  however,  a  consider- 
able number  of  compounds  are  known  which  contain  two  or 
more  such  nuclei  united  in  a  variety  of  ways.  Such  com- 
pounds are  usually  arranged  in  the  following  groups: — 

1.  Diphenyl  group;  this  comprises  the  compounds  with  two 
benzene  nuclei  directly  united  together.  The  parent  substance 
of  the  group  is  diphenyl,  C6H6.C6H6. 


Dli>HENYL  471 

2.  Diphenyl-methane  group;   this  includes  all  compounds 
with  two  benzene  nuclei  attached  to  a  single  carbon  atom. 
The  parent  substance  is  diphenyl-methane,  C6H5  •  CH2  •  C6H5. 

3.  Dibenzyl  or  stilbene  group,  which  comprises  compounds 
containing  two  benzene  nuclei  linked  together  by  a  chain  of 
two  or  more  carbon  atoms,  e.g.  dibenzyl,  Cfi!L  •  CH2  •  CH2  •  CJEL, 
and  stilbene,  C6H5 .  CH :  CH .  C6H5. 

4.  Triphenyl-methane  group,  which  contains  the  compounds 
with  three  benzene  nuclei  attached  to  a  single  carbon  atom, 
e.g.  triphenyl-methane,  CH(C6H5)3. 

5.  In  addition  to  the  above  groups  several  extremely  im- 
portant groups  are  known  which  contain  two  or  more  benzene 
nuclei  arranged  in  such  a  manner  that  they  have  two  or  more 
carbon  atoms  in  common,  e.g.: 


Naphthalene,  ;        anthracene,  ;    &c. 


These  are  usually  termed  compounds  with  condensed  benzene 
nuclei. 

DIPHENYL  GEOUP 

Diphenyl  is  related  to  benzene  in  much  the  same  manner 
as  ethane  to  methane: 

CH4  and  CH3  -  CH3  C6H6  and  C6H6  •  C6H6. 

Its  molecule  consists  of  two  benzene  nuclei  directly  united 
Its  method  of  synthesis  by  Fittig,  by  the  action  of  sodium  on 
an  ethereal  solution  of  monoiodo-benzene  or  of  copper-bronze 
at  230°  (Ullmann,  A.  332,  38),  is  analogous  to  the  formation 
of  ethane  by  the  action  of  zinc  or  sodium  on  methyl  iodide: 
2C6H6I  +  2Cu  =  C6H6.C6H5  +  Cu2I2. 


It  is  also  formed  by  passing  the  vapour  of  benzene  through  a 
red-hot  tube.  It  is  contained  in  coal-tar,  crystallizes  in  large 
colourless  plates,  melts  at  71°,  boils  at  254°,  and  is  readily 
soluble  in  alcohol  and  ether. 

Chromic  acid  oxidizes  diphenyl  to  benzoic  acid,  one  of  the 
two  benzene  nuclei  being  destroyed,  thus  leaving  only  one 
carbon  atom  joined  to  the  other  benzene  residue.  From  this 
and  from  its  synthesis,  the  constitutional  formula  of  diphenyl 
must  be  C6H5-C6H6. 


472  XXVII.   DIPHENYL  GROUP 

Derivatives  (Schulte,  A.  207,  311). — Like  benzene,  diphenyl 
is  the  mother  substance  of  an  extended  series  of  derivatives 
which  closely  resemble  the  corresponding  benzene  derivatives 
in  most  respects.  With  polysubstituted  derivatives  the  sub- 
stituents  are  usually  denoted  by  the  following  numbers,  accord- 
ing to  the  position  occupied : 


Even  the  entrance  of  only  one  substituent  produces  isomers, 
since  the  latter  may  stand  either  in  the  0-,  m-,  or  ^-position  to 
the  point  of  union  of  the  two  benzene  residues.  The  same 
applies  in  still  greater  degree  to  isomeric  di-derivatives,  of 
which  o-o-,  p-p-,  o-p-,  &c.  compounds  can  exist.  The  consti- 
tution of  these  is  elucidated  from  their  syntheses,  from  their 
products  of  oxidation,  or  by  conversion  into  compounds  of 
known  constitution;  thus  a  chloro-diphenyl,  C12H9C1,  which 
yields  ^>-chloro-benzoic  acid  when  oxidized  by  chromic  acid,  is 
obviously  ^-chloro-diphenyl.  Whether  all  the  substituents  are 
attached  to  the  one  nucleus  or  are  distributed  between  the 
two,  can  also  be  proved  by  an  examination  of  the  products  of 
oxidation. 

The  substituents  take  up  the  ^-position  for  choice;  in  di- 
derivatives  the  p-p-  (and  to  a  lesser  extent  the  o-p-)  position. 

Di-p-diamino- diphenyl,  benzidine,  NH2  •  C6H4  •  C6H4  •  NH2 
(Zinin,  1845),  is  obtained  by  the  reduction  of  ^-j9-dinitro- 
diphenyl  (the  direct  nitration  product  of  diphenyl);  also,  to- 
gether with  diphenyline,  by  the  action  of  acids  upon  hydrazo- 
benzene,  the  latter  undergoing  a  molecular  transformation 
(p.  395): 

C6H6.NH.NH.C6H6  =  NH2.C6H4.C6H4.NH2; 

it  is  consequently  formed  directly  from  azobenzene  by  treating 
it  with  tin  and  hydrochloric  acid. 

Benzidine  is  a  diacid  base  which  crystallizes  in  colourless 
silky  plates,  is  readily  soluble  in  hot  water  or  alcohol,  melts 
at  122°,  and  can  readily  be  sublimed.  Its  sulphate, 
C12H10(NH2)2  •  S04H2,  is  sparingly  soluble.  Like  its  homo- 
logues  (tolidine,  &c.),  it  is  of  special  importance  in  the  colour 
industry,  since,  by  coupling  its  diazonium-compound  (tetra- 
zonium-diphenyl  chloride)  with  naphthol-sulphonic  or  naph- 
thylamine-sulphonic  acids,  &c.,  colours  are  produced  which 


CARBAZOLE.      DIPHENYLENE  OXIDE  473 

dye  unmordanted  cotton  directly,  the  so-called  "  substantive  " 
or  cotton  dyes.  To  this  class  belongs  the  dye  congo, 

(S03Na)(NH2)C10H6  •  N :  N  •  C6H4 .  C6H4 .  N :  N  •  C10H6(NH2)(S03Na), 

prepared  by  means  of  naphthionic  acid  (p.  499),  and  the  dye 
chrysamine  G,  prepared  with  salicylic  acid. 

The  isomeric  diphenyline,  2 : 4'-diamino-diphenyl,  may  be 
obtained  from  2 : 4'-dinitro-diphenyl,  and  also  as  a  by-product 
in  the  preparation  of  benzidine  from  azobenzene.  It  crystal- 
lizes in  needles,  melting  at  45°,  and  yields  a  sulphate  which  is 
readily  soluble. 

Carbazole, 


NH 


the  imide  of  diphenyl,  is  contained  in  coal-tar  and  in  crude 
anthracene.  It  is  formed  by  distilling  o-amino-diphenyl  over 
lime  at  a  low  red  heat,  or  by  passing  the  vapour  of  diphenyl- 
amine  through  red-hot  tubes,  just  as  diphenyl  is  obtained 
from  benzene: 

(C6H6)2NH  =  (C6H4)2NH  +  H2. 

It  crystallizes  in  colourless  plates  sparingly  soluble  in  cold 
alcohol,  melts  at  238°,  distils  unchanged,  and  is  characterized 
by  the  readiness  with  which  it  sublimes.  Concentrated  sul- 
phuric acid  dissolves  it  to  a  yellow  solution,  and  it  forms  an 
acetyl-  and  a  nitro-compound,  &c.  The  nitrogen  in  it  occupies 
the  di-ortho-position ;  it  thus  appears,  like  indole,  to  be  a  pyr- 
role derivative,  and  it  shows,  in  fact,  most  striking  analogies 
to  the  latter  (B.  21,  3299). 

Benzidine-mono-,  di-,  &c.  sulphonic  acids,  e.g.  C12H6(NH2)2 
(S03H)2,  are  of  technical  importance.  The  dihydroxy- 
diphenyls,  C12H8(OH)2,  of  which  four  isomers  are  known,  are 
formed  (a)  by  diazotizing  benzidine,  (b)  by  fusing  diphenyl- 
disulphonic  acid  with  potash,  and  (c)  by  fusing  phenol  with 
potash  or  by  oxidizing  it  with  permanganate;  in  the  last  case 
hydrogen  is  separated  and  two  benzene  residues  join  together. 

p    TT 

Diphenylene  oxide,  • 6    4/0,  is  obtained  by  distilling  phenol 
C6H/ 

with  plumbous  oxide;  it  crystallizes  in  plates  which  distil  with- 
out decomposition  (cf.  e.g.  B.  25,  2745). 

The  carboxylic  acids  of  diphenyl  are  obtained  (1)  from  the 


474  XXVIII.   DIPHENYL-METHANE   GROUf 

corresponding  nitriles,  which  on  their  part  are  prepared  by 
distilling  the  sulphonic  acids  of  diphenyl  with  KCN,  e.g.  di-p- 
diphenyl-dicarboxylic  acid,  C12H8(C02H)2,  a  white  powder 
insoluble  in  water,  alcohol,  and  ether;  (2)  by  the  oxidation  of 
phenanthrene  and  similar  compounds,  e.g.,  diphenic  acid, 
C02H-C6H4.C6H4.C02H,  the  2 : 2'-dicarboxylic  acid,  crystal- 
lizing in  needles  or  plates  which  are  readily  soluble  in  the 
solvents  just  mentioned;  rn.-pt.  229°.  Both  of  these  are  di- 
basic acids,  which  yield  diphenyl  when  heated  with  soda-lime. 

The  homologues  of  diphenyl  are,  like  the  latter,  obtained  by 
means  of  Fittig's  reaction.  Analogous  to  benzidine  is  0-tolidine, 
Ci2H6(CH3)2(NH2)2,  m.-pt.  128°,  whose  diazo-compound  unites 
with  naphthionic  acid  to  the  red  substantive  dye,  benzo-pur- 
purine  4B.  Similarly  di-anisidine  or  dimethoxy-benzidine, 
C12H6(0  •  CH3)2(NH2)2,  yields  diazonium  salts  which  combine 
with  a-naphthol-a-sulphonic  acid  to  form  a  blue  substantive 
dye,  benzazurine  G. 

Diphenyl  may  be  regarded  as  monophenyl -benzene;  the 
corresponding  di-  and  triphenyl-benzenes  are  also  known. 

^-Diphenyl-benzene,  CCH4(C6H5)2,  may  be  obtained  by  the 
action  of  sodium  upon  a  mixture  of  ^-dibromo-benzene  and 
bromo-benzene.  It  crystallizes  in  flat  prisms,  melts  at  205°, 
and  on  oxidation  yields  diphenyl-monocarboxylic  and  tere- 
phthalic  acids. 

When  hydrochloric  acid  gas  is  led  into  acetophenone,  C6H5  • 
CO  •  CH3,  a  reaction  analogous  to  the  formation  of  mesitylene 
from  acetone  (p.  342)  ensues,  and  s-triphenyl-benzene, 
C6H3(C6H5)3  (rhombic  plates),  is  formed. 


XXVIII.   DIPHENYL-METHANE  GROUP 

Diphenyl-methane,  C6H5  •  CH2  •  C6H5,  is  derived  from  methane 
by  the  replacement  of  two  hydrogen  atoms  by  two  phenyl 
groups,  and  is  thus  closely  related  to  phenyl-methane  or  toluene, 
C6H5  •  CH3.  One  important  difference  is  that  when  oxidized  it 
cannot  yield  an  acid  containing  the  same  number  of  carbon 
atoms  since  it  does  not  contain  a  methyl  group.  It  can  be 
oxidized  to  the  secondary  alcohol  benzhydrol,  (C6H5)2CHOH, 
or  the  ketone  benzophenone,  (C6H5)2CO.  Compounds  like 
diphenyl-ethane,  (C6H5)2CH  •  CH3,  can  yield  acids. 

The  various  derivatives  are  obtained  by  substituting  one 


DIPHENYL-METHANE  475 

or  more  of  the  twelve  hydrogen  atoms  present  in  the  diphenyl- 
methane  molecule.  If  the  substituent  replaces  any  of  the  ten 
hydrogens  directly  attached  to  the  benzene  nuclei,  a  com- 
pound is  formed  which  closely  resembles  the  corresponding 
derivatives  of  benzene,  e.g.  C6H5  •  CH2  •  C6H4  •  NH2  closely  re- 
sembles aniline.  If,  on  the  other  hand,  the  substituent  replaces 
a  hydrogen  atom  of  the  methylene  group,  a  compound  with 
aliphatic  properties  is  obtained,  e.g.  (C6H5)2CH«OH  closely 
resembles  a  secondary  aliphatic  alcohol. 

The  method  of  numbering  the  carbon  atoms  in  the  diphenyl- 
methane  molecule  is  usually  as  follows : — 


Formation  of  diphenyl-methane  and  its  derivatives. 

1.  Diphenyl-methane  is  produced  by  the  action  of  benzyl 
chloride  upon  benzene,  in  presence  of  zinc  dust  (Zincke,  A.  159, 
374),  or  of  aluminium  chloride  (Friedel  and  Crafts): 

=  C6H6.CH2.C6H5  + 


The  homologues  of  benzene,  and  also  the  phenols  and 
tertiary  amines,  may  be  used  instead  of  benzene  itself. 

In  an  exactly  analogous  manner  diphenyl-methane  is  ob- 
tained by  the  action  of  methylene  chloride,  CH2C12,  upon 
benzene  in  presence  of  aluminium  chloride: 

CH2C12  +  2C6H6  =  CH2(C6H6)2 


2.  Diphenyl-methane  hydrocarbons  are  formed  by  the  action 
of  the  aliphatic  aldehydes,  e.g.  acetaldehyde  or  formaldehyde, 
upon  benzene,  &c.,  in  the  presence  of  concentrated  sulphuric 
acid  (Baeyer,  B.  6,  963).  With  formaldehyde  diphenyl-methane, 
or  with  acetaldehyde  diphenyl-ethane,  is  formed: 

CH3.CHO  +  2C6H6  =  CH3.CH(C6H6)2  + 


The  acetaldehyde  and  formaldehyde  are  employed  here  in 
the  form  of  paraldehyde  and  methylal.  Formaldehyde  itself 
condenses  with  aniline  to  diamino-,  and  with  dimethyl-aniline 
to  tetramethyl-  diamino  -diphenyl-methane.  When  aromatic 
aldehydes  are  used,  triphenyl-methane  derivatives  are  formed 
(p.  480). 

3.  Aromatic  alcohols  react  with  benzene  and  sulphuric  acid 
in  an  analogous  manner  (V.  Meyer): 
C6H6.CH2-OH 


476  XXVIII.   DIPHENYL-METHANB  GROUP 

Similar  reactions  have  also  been  brought  about  by  means  of 
ketones,  aldehydo-acids,  and  keto-acids  on  the  one  hand,  and 
phenol  and  dialkylated  anilines  on  the  other. 

The  true  aromatic  ketones  of  the  type  of  benzophenone  may 
be  regarded  as  diphenyl-methane  derivatives  (see  p.  428). 

Diphenyl-methane,  (CgH5)2CH2,  is  most  conveniently  pre- 
pared from  benzyl  chloride,  benzene,  and  aluminic  chloride. 
It  crystallizes  in  colourless  needles  of  very  low  melting-point 
(26°),  is  readily  soluble  in  alcohol  and  ether,  has  a  pleasant 
odour  of  oranges,  and  distils  unaltered  at  262°. 

It  yields  nitro-,  amino-,  and  hydroxy-derivatives.  ^-Diamino- 
diphenyl-methane,  CH2(C6H4NHA2,  is  obtained  by  heating 
anhydro-formaldehyde-aniline,  C6Hg  •  N  :  CH2,  prepared  from 
formaldehyde  and  aniline,  with  aniline  and  an  aniline  salt. 
It  crystallizes  in  lustrous  silvery  plates,  melting  at  87*,  and 
may  be  used  for  the  preparation  of  fuchsine.  Bromine  at  a 
moderate  temperature  reacts  with  the  hydrocarbon  yielding 
diphenyl-bromo-  methane,  (C6H5)oCHBr,  and  when  this  is 
heated  with  water  to  150°,  it  yields  benzhydrol,  diphenyl-car- 
binol,  (C6H6)2CH«OH,  which  can  also  be  obtained  from  benzo- 
phenone and  sodium  amalgam,  or  by  Grignard's  synthesis.  It 
crystallizes  in  glistening  silky  needles,  melts  at  68°,  possesses 
in  every  respect  the  character  of  a  secondary  alcohol  (forming 
esters,  amines,  &c.),  and  is  readily  oxidized  to  the  correspond- 
ing ketone,  benzophenone,  (C6IL)2CO  (p.  428). 

aa-Diphenyl-ethane,  (C6H5)2CH  •  GEL  (isomeric  with  dibenzyl, 
see  p.  477),  is  obtained  by  method  of  formation  2  (p.  475).  It 
is  a  liquid,  boils  at  286°,  and  is  oxidized  to  benzophenone  by 
chromic  acid.  From  it  is  derived : 

Benzilic  acid,  diphenyl-gly collie  add,  (C6H5)2C(OH)  •  C02H, 
which  is  formed  by  a  molecular  transformation  when  benzil, 
C6H5.CO.CO-C6H5  (p.  479),  is  fused  with  potash.  It  crystal- 
lizes in  needles  or  prisms,  dissolves  in  concentrated  sulphuric 
acid  to  a  blood-red  solution,  and  is  reduced  by  hydriodic  acid 
to  diphenyl-acetic  acid,  (C6H6)2CH  •  C02H  (needles  or  plates), 
which  may  also  be  obtained  synthetically  from  phenyl-brom- 
acetic  acid,  C6IL»CHBr  'GOgH,  benzene,  and  zinc  dust,  accord- 
ing to  mode  of  formation  1,  p.  475. 

Tolyl-phenyl-methanes,  C8H5  •  CH2  •  C6H4  •  CH3.  The  p-  and  o- 
compounds  are  obtained  from  benzyl  chloride  and  toluene. 

Benzoyl-benzoic  acids,  benzophenone-carboxylic  acids,  C6H5« 
CO.C6H4.C02H  (B.  6,  907).  Of  these  the  o-acid  (m.-pt.  127°) 
has  been  prepared  synthetically  by  heating  phthalic  anhydride 


DIBENZYL  GROUP  477 

with   benzene   and   aluminic   chloride.      When   heated  with 
phosphorus    pentoxide    at    180°,    it    yields    anthra-quinone, 

H      various  transformations   into  the  anthra- 


cene series  have  been  effected  in  a  similar  manner  from  o-tolyl- 
phenyl-methane  and  the  corresponding  ketone. 

C6H4\ 
Fluorene,    diphenylene-methane,     •       /CH2,   stands  in  the 

CgH/ 

same  relation  to  diphenyl-methane  as  carbazole  (p.  473)  does 
to  diphenylamine;  it  is  at  the  same  time  a  diphenyl  and  a 
methane  derivative.  It  is  contained  in  coal-tar,  and  is  pro- 
duced when  diphenyl-methane  is  led  through  red-hot  tubes 
(like  diphenyl  from  benzene),  and  also  by  passing  the  vapour 
of  diphenylene-ketone  over  red-hot  zinc  dust.  It  crystallizes 
in  colourless  plates  with  a  violet  fluorescence,  melts  at  113°, 
and  boils  at  295°.  The  corresponding  ketone,  diphenylene- 
ketone,  C12H8:CO,  which  crystallizes  in  yellow  prisms  melting 
at  84°,  is  obtained  by  heating  phenanthra-quinone  with  lime, 
and  is  converted  into  fluorenyl  alcohol,  (C6H4)2  :  CH  •  OH 
(colourless  plates,  m.-pt.  153°),  by  nascent  hydrogen,  and  into 
diphenyl-carboxylic  acid,  o-phenyl-benzoic  acid,  C6 
C02H,  by  fusion  with  potash. 


XXIX.  DIBENZYL  GROUP 

This  group  comprises  the  compounds  containing  two  ben- 
zene nuclei  connected  by  a  chain  of  two  carbon  atoms. 
Among  the  most  important  members  are:  —  Dibenzyl, 
C6H5.CH2.CH2.C6H5;  stilbene,  C6H5.CH:CH.C6H5;  tolane, 


C6H5  •  C  :  C  •  C6EU;  deoxybenzoin,  C6H5  •  CH2  •  CO  •  C6H5, 
hydrobenzoin,  C6H5  •  CH(OH)  •  CH(OH)  •  C6H5;  benzoin, 
C6Hff.CH(OH).CO.C6H,;  benzil,  C6H5.CO.CO.C6H5. 

Dibenzyl  is  symmetrical  diphenyl-ethane  (for  the  unsym- 
metrical  compound,  see  p.  476),  stilbene  is  s-diphenyl-ethylene, 
and  tolane  diphenyl-acetylene. 

All  these  compounds  yield  benzoic  acid  when  oxidized. 

Dibenzyl  is  formed  when  benzyl  chloride  is  treated  with 
metallic  sodium,  or  by  the  action  of  benzyl  chloride  on  benzyl 
magnesium  chloride.  It  is  often  met  with  as  a  by-product  in 
Grignard's  synthesis  by  means  of  benzyl  magnesium  chloride. 


478  XXIX.   DIBENZYL  GROUP 

It  is  isoineric  with  ditolyl  and  with  tolyl-plienyl-methane ; 
it  crystallizes  in  needles  or  small  plates,  melts  at  52°,  and 
sublimes  unchanged. 

Stilbene,  s-diphenyl-ethylene,  forms  monoclinic  plates  or  prisms, 
melts  at  125°,  and  also  boils  without  decomposition.  It  may 
be  prepared  by  the  action  of  sodium  upon  benzal  chloride,  or 
by  heating  deoxybenzoin  with  sodium  ethoxide,  or  best  by 
the  action  of  benzyl  magnesium  chloride  on  benzaldehyde, 
and  possesses  the  full  character  of  an  olefine,  giving,  for 
instance,  a  dibromide,  C6H5  •  CHBr  •  CHBr  •  C6H5,  with  bro- 
mine, and  being  converted  into  dibenzyl  by  hydriodic  acid. 
^-Diamino-  stilbene,  C14H10(NH2)2,  and  its  disulphonic  acid 
(obtained  by  reducing  ^-nitro-toluene  or  its  sulphonic  acid  in 
alkaline  solution)  are,  like  benzidine,  mother  substances  of 
"substantive  dyes"  (see  p.  473).  Stilbene  should  exist  in  two 
stereo-isomeric  modifications,  the  ordinary  stilbene  melting  at 

H  .C-Ph 
125°  is  usually  regarded  as  the  trans  compound 

Ph  •  C  •  H 

An  isomeride — the  cis  compound  has  been  described  by  Otto 
and  Sto/el  (B.  1897,  30,  1799).  Just  as  ethylene  bromide 
yields  acetylene  when  boiled  with  alcoholic  potash,  so  stilbene 
dibromide  yields  tolane,  which  crystallizes  in  prisms  or  plates, 
melting  at  60°.  It  may  also  be  prepared  by  the  following 
series  of  reactions: — 
C6H6.CH2.CO.C6H6  —  C6H5.CH:CC1.C6H6  —  C6H6.C:C.C6H6. 

Phosphorus  pentachloride  Alcoholic  potash 

Tolane  corresponds  with  acetylene  in  its  properties  in  so  far 
that  it  combines  with  chlorine  to  a  dichloride  and  a  tetra- 
chloride;  but  it  does  not  yield  metallic  derivatives,  since  it 
contains  no  "acetylene  hydrogen"  (p.  51). 

When  stilbene  dibromide  is  treated  with  silver  acetate,  two 
di-acetates  are  formed;  and  when  these  are  hydrolysed  by 
alcoholic  ammonia,  two  isoineric  substances  of  the  composition, 
C6H5.CH(OH).CH(OH).C6H5,  hydrobenzoin  and  iso-hydro- 
benzoin  or  s-diphenyl-glycol,  are  produced.  Both  compounds 
are  also  formed  by  the  action  of  sodium  amalgam  upon  oil  of 
bitter  almonds.  The  former  crystallizes  in  rhombic  plates, 
melting  at  138°,  and  the  latter  in  four-sided  prisms,  melting 
at  119°,  and  is  the  more  soluble  of  the  two.  The  two  com- 
pounds are  stereo-isomeric  in  the  same  manner  as  meso-tartaric 
and  racemic  acid,  and  JSrlenmeyer,  Junr.,  has  been  able  to  re- 
solve hydrobenzoin,  which  corresponds  Mith  racemic  acid,  into 


BENZIL.      DEOXYBENZOIN  479 

two  optically  active  components,  by  separating  two  different 
kinds  of  hemihedral  crystals  (A.  198,  115,  191;  B.  30,  1531). 
The  compounds  benzoin,  benzil,  and  deoxy benzoin,  which 
have  already  been  mentioned,  are  closely  related  to  one  an- 
other, as  their  formulae  show,  and  can  also  be  prepared  from 
benzaldehyde.    When  the  aldehyde  is  boiled  with  an  alcoholic 
solution  of  potassium  cyanide  it  polymerises,*  yielding  benzoin, 
2C6H6.CH:0  =  C6H6.CH(OH).CO.C6H6, 

which  forms  beautiful  glistening  prisms,  m.-pt.  134°;  nascent 
hydrogen  reduces  it  to  hydrobenzoin,  from  which  it  can  also 
be  obtained  by  oxidation.  It  reduces  Fehling's  solution  even 
at  the  ordinary  temperature,  yielding  benzil. 

Benzil,  C6H5  •  CO  •  CO  •  C6H5,  is  obtained  by  oxidizing  ben- 
zoin with  nitric  acid.  It  crystallizes  in  large  six-sided  prisms, 
melting  at  95°.  It  is  oxidized  to  benzoic  acid  by  chromic 
anhydride,  and  reduced  by  nascent  hydrogen — according  to 
the  conditions — either  to  benzoin  or  to  deoxybenzoin.  It 
reacts  with  hydroxylamine  to  produce: 

Benzil-monoxime,  C6H§.CO^C(:N.OH).C6H5,  and  benzil- 
dioxime,  C6H5.C(:N.OH).C(:N.OH).C6H5,  which  exist  in 
the  following  sfeereo-isomeric  modifications  (Hantzsch  and 
Werner,  B.  23,  11;  37,  4295;  Dittrich,  ibid.,  24,  3267):— 

Monoximes : 

C6H6.C.CO-C6H6  C6H6.C.CO.C6H6 

N-OH         Heated   HO-N 

eu  M.-pt.  134*  y.  M.-pt.  113*. 

Dioximes : 

C6H5.C C.C6H5  _^  C6H6.C  •  C.C6H5  ^_  C6H5.C C.C6H6 

N-OH  HO-N  "   HO-N  N-OH  "  "   HO-N   HO-N 

ou  M.-pt.  237°  j3.  M.-pt.  207°  y.  M.-pt.  163°. 

The  configurations  have  been  established  as  the  result  of  an 
examination  of  the  products  obtained  by  the  Beckmann  trans- 
formation (A.  296,  279;  274,  1.  Compare  pp.  139  and  429). 

Deoxybenzoin,  C6H5  •  CH2  •  CO  •  C6H5,  forms  large  plates, 
melting  at  55°,  and  may  be  sublimed  or  distilled  unchanged. 
It  can  be  prepared  by  the  action  of  benzene  and  aluminium 
chloride  upon  phenyl-acetyl  chloride,  C6H5  •  CHg  •  CO  •  Cl,  and 
hence  its  constitution,  and  yields  di-benzyl  with  hydriodic 
acid.  Deoxybenzoin  can  also  be  prepared  from  benzil  and 
benzoin  (B.  25,  1728).  One  of  its  methylene  hydrogen  atoms 

*  For  mechanism,  cf.  Chalanay  and  Knoevenayd  (B.  1892,  25,  295). 


480  XXX.    TRIPHENYL-METHANE  GROUI 

is  retadilv  replaceable  by  alkyl,  just  as  in  acetoacetic  ester. 
The  radical,  CH(C6H5) .  CO  •  C6H5,  is  termed  "desyl". 

Benzilic  acid,  (C6H5)2C(OH)  •  C02H  (p.  476),  is  produced 
when  benzil  is  heated  with  alcoholic  potash,  by  a  peculiar 
molecular  transformation  similar  to  that  by  which  pinacoline 
is  formed  (p.  193). 

Compounds  closely  related  to  the  dibenzyl  group  are  those 
which  contain  two  benzene  nuclei  united  by  a  chain  of  more 
than  two  carbon  atoms,  e.g.  ay-dipbenyl  propane,  and  also 
those  compounds  containing  three  or  more  benzene  nuclei 
united  by  a  chain  of  carbon  atoms,  e.g.  triphenyl-ethane,  tetra- 
phenyl-ethane,  &c. 


XXX.  TRIPHENYL-METHANE  GROUP 

Triphenyl-methane,  CH(C6H5)3,  is  the  compound  obtained 
as  the  result  of  the  entrance  of  three  phenyl  groups  into  the 
methane  molecule;  among  its  homologues  are  tolyl-diphenyl- 
methane,  (C6H.)2CH  -  C6H4  •  CH«,  ditolyl  -  phenyl  -  methane, 
C6H5.CH(06H4.CHS).,,  &c. 

These  hydrocarbons  are  of  especial  interest  as  being  the 
mother  substances  of  an  extensive  series  of  dyes;  the  amino-, 
hydroxy-,  and  carboxy-derivatives  of  triphenyl-  methane  are 
the  leuco-bases  obtained  from  such  dyes  as  rosaniline,  aurine, 
malachite  green,  &c. 

Their  formation  is  effected  in  a  manner  analogous  to  that  of 
the  diphenyl-methane  derivatives,  i.e.  by  the  aid  of  zinc  dust 
or  aluminic  chloride  when  chlorine  compounds  are  used,  or 
by  the  aid  of  phosphoric  anhydride  when  oxygen  compounds 
are  employed. 

Thus,  triphenyl-methane  may  be  obtained  (a)  from  benzal 
chloride  and  benzene  in  the  presence  of  aluminic  chloride, 

C6H6.CHC12  +  2C6H6  =  CH(C6H6)3  + 


or  from  benzaldehyde,  benzene,  and  zinc  chloride;   (b)  from 
chloroform  and  benzene  in  presence  of  aluminic  chloride, 

3C6H6  +  CHC13  =  CH(C6H6)3  +  3HC1; 

(c)  from  benzhydrol  and  benzene  in  the  presence  of  phos- 
phoric anhydride, 

(C6H6)2CH.OH-f  C6H6  =  (C6H6)2CH.(C6H6)  +  HaO. 


I'RIPHENYL-METHANE  481 

Derivatives  of  triphenyl  -  methane  may  be  obtained  by 
similar  methods,  e.g.  the  leuco-base  of  bitter-almond-oil  green, 
tetramethyl-diamino-triphenyl-methane  (cf.  p.  483),  may  be 
prepared  by  the  condensation  of  benzaldehyde  and  dimethyl- 
aniline  : 

C6H6.CHO  +  2C6H6.N(CH3)2  =  C6H6.CH:[C6H4.N(CHs)2]2-f  H2O. 

When  other  amines  or  even  phenols  are  used,  a  series  of 
allied  compounds  (which  are  often  dyes)  is  obtained,  the  sepa- 
ration of  water  being  facilitated  by  the  addition  of  zinc  chlo- 
ride, concentrated  sulphuric  acid,  or  anhydrous  oxalic  acid. 

Triphenyl -methane,  CH(C6H5)3  (KekuU  and  Franchimont, 
B.  5,  906).  This  compound  may  be  prepared  from  chloroform 
and  benzene  by  the  Friedel-Cmfts  reaction  (cf.  A.  194,  152), 
diphenyl-methane  being  produced  at  the  same  time;  also  by 
eliminating  the  amino-groups  from  ^-leucaniline,  C19H13(NH2)3, 
and  most  readily  by  reducing  triphenyl-carbinol  with  zinc  dust 
and  acetic  acid.  It  crystallizes  in  colourless  prisms,  m.-pt.  93°, 
b.-pt.  359°,  and  dissolves  readily  in  hot  alcohol,  ether,  and 
benzene. 

It  crystallizes  from  benzene  with  one  molecule  of  "  benzene 
of  crystallization",  which  is  also  the  case  with  many  triphenyl- 
methane  derivatives.  When  triphenyl-methane  is  treated  with 
bromine  in  a  solution  of  carbon  bisulphide,  the  methane  hy- 
drogen atom  is  exchanged  for  bromine  with  the  formation  of 
triphenyl-methyl  bromide,  (C6H5)3-CBr,  which,  when  boiled 
with  water,  yields  triphenyl-carbinol,  (C6H5)3C-OH.  This 
crystallizes  in  glistening  prisms,  melts  at  159°,  and  can  be 
sublimed  unchanged;  it  may  also  be  prepared  directly  by 
oxidizing  a  solution  of  triphenyl-methane  in  glacial  acetic  acid 
with  chromic  acid,  or  synthetically  by  the  action  of  Grignard's 
phenyl  magnesium  bromide  on  benzophenone  or  ethyl  benzoate : 

(C6H6)2CO  —  (C6H6)3C.OMgBr  —  (C6H6)3C.OH. 

A  number  of  homologues  of  triphenyl-methane  have  been- 
prepared  by  this  last  method  (Houben,  B.  1903,  36,  3087). 

Fuming  nitric  acid  converts  triphenyl-methane  into  trinitro- 
triphenyl-methane,  (C6H4»N02)3*CH  (yellow  scales),  which 
can  then  be  oxidized  by  chromic  acid  to  trinitro-triphenyl- 
carbinol,  (C6H4  •  N02)3C  •  OH.  The  latter  gives  para-rosaniline, 
(C6H4  •  NH2)3C  •  OH,  when  reduced  with  zinc  dust  and  glacial 
acetic  acid. 

Homologous  with  triphenyl-methane  are  the  tolyl-diphenyl- 

(B480)  2H 


482  XXX.   TRIPHENYL-METHANE  GROUP 

methanes,  (C6H5)2CH'C6H4«CH3.  From  these  also  dyes  are 
derived,  especially  from  m-tolyl-diphenyl-methane  (in  which 
the  CH3  occupies  the  meta-position  with  regard  to  the  methane 
carbon  atom),  which  can  be  prepared  by  diazotizing  ordinary 
leucaniline;  it  crystallizes  in  small  prisms  and  melts  at  59 -5° 

TRIPHENYL-METHANE  DYES 

Of  the  derivatives  of  triphenyl-me thane  and  of  tolyl-di- 
phenyl-methane,  those  are  especially  interesting  which  contain 
amino-,  hydroxy-,  or  carboxy-groups.  The  entrance  of  three 
amino-  or  hydroxy-groups  converts  them  into  the  leuco-com- 
pounds  of  dyes,  some  of  which  latter  are  of  great  value.  Two 
amino -groups  suffice  for  the  full  development  of  the  dye 
character  only  when  the  amino-hydrogen  atoms  are  replaced 
by  alkyl  radicals,  one  amino-group  being  insufficient  for  this 
(see  under  ^-amino-triphenyl-methane). 

The  following  are  the  chief  groups  of  triphenyl-methane 
dyes: — 

1.  Those  derived   from  diamino- triphenyl-methane.     The 
malachite-green  group. 

2.  Those  derived  from  triamino- triphenyl-methane.     The 
rosaniline  group. 

3.  Those  derived  from  trihydroxy-triphenyl-methane.     The 
aurine  group. 

4.  Those  derived  from  triphenyl-methane-carboxylic  acid. 
The  eosin  group. 

Leuco-bases  or  leuco-compounds  of  dyes  (p.  399)  are  the 
colourless  compounds  formed  by  the  reduction  of  the  dyes, 
usually  by  the  addition  of  two  atoms  of  hydrogen.  When 
oxidized  they  are  converted  back  into  the  dyes. 

All  the  dyes  of  the  triphenyl-methane  group,  and  also 
indigo,  methylene  blue,  safranine,  &c.,  are  capable  of  yielding 
such  leuco-compounds,  generally  on  reduction  with  zinc  and 
hydrochloric  acid,  stannous  chloride,  or  ammonium  sulphide. 

The  oxidation  of  the  leuco-compounds  is  often  quickly 
effected  by  the  oxygen  of  the  air  (e.g.  in  the  cases  of  indigo 
white  and  of  leuco-methylene  blue) ;  in  the  triphenyl-methane 
group  it  is  slower  and  frequently  more  complicated  Leuco- 
malachite  green  is  readily  oxidized  to  the  corresponding 
colour-base  when  treated  with  lead  peroxide  in  acid  solution, 
and  leucaniline  when  warmed  with  chloranil  in  alcoholic 
solution,  or  when  its  hydrochloride  is  heated  either  alone  or 


AMINO-  AND  DIAMINO-TRIPHENYL-METHANE  DYES       483 

with  a  concentrated  solution  of  arsenic  acM,  or  with  metallic 
hydroxides  such  as  ferric  hydroxide. 

The  leuco-bases  of  the  triphenyl-methane  dyes  are  deriva- 
tives of  triphenyl-methane  or  its  homologues,  the  corresponding 
dye-bases  obtained  by  oxidizing  the  leuco-bases  are  derivatives 
of  triphenyl-carbinol  or  its  homologues,  and  the  dyes  them- 
selves are  salts  obtained  by  the  elimination  of  water  from  the 
dye-base  and  an  acid.  The  relationships  between  the  three 
groups  of  compounds  —  leuco-base,  dye-base,  and  dyes  —  are  in- 
dicated in  the  following  scheme: 

oxidized  acid 

Leuco-base  ^±  dye-base  ^±  dye. 
reduced  alkali 

As  an  example: 
CH(C0H4.NH2)3  -  O 

'   U  T  J^^1 

-H20 
1.  AMINO-  AND  DIAMINO-   TRIPHENYL-METHANE   GROUP 

^-Amino-triphenyl-methane  can  be  synthesized  either  by 
the  condensation  of  jp-nitro-benzaldehyde  with  benzene  and 
subsequent  reduction,  or  from  benzhydrol  and  aniline.  It 
forms  large  prisms,  and  melts  at  84°.  The  corresponding  car- 
.binol  is  colourless  and  with  acids  yields  red  salts,  but  these 
cannot  dye  animal  fibres. 

^-Diamino-  triphenyl-methane,  C6H5  •  CH(C6H4  •  NH2)2,  is 
prepared  by  the  action  of  zinc  chloride  or  of  fuming  hydro- 
chloric acid  upon  a  mixture  of  benzaldehyde  and  aniline 
sulphate  or  chloride: 

=  C6Hfi.CH(C6H4.NH2)2  +  H2O. 


It  crystallizes  in  prisms,  and  the  colourless  salts  yield  an 
unstable  blue-violet  dye,  benzal  violet,  when  oxidized.  Me- 
thylation  converts  the  base  into: 

Tetramethyl  -  di-p-amino  -  triphenyl  -  methane,  leuco-malachite 
green,  C6H5«CH[C6H4-N(CH3)2]2,  which  is  prepared  on  the 
technical  scale  by  heating  benzaldehyde  and  dimethyl-aniline 
with  zinc  chloride  or  concentrated  sulphuric  acid  (0.  Fischer,  A. 
206,  103).  It  forms  colourless  plates  or  prisms.  As  a  diacid 
base  it  yields  colourless  salts,  which  are  slowly  converted  by 
the  air,  but  immediately  by  other  oxidizing  agents,  such  as 
lead  dioxide  and  sulphuric  acid,  into  the  salts  of  tetramethyl- 
Oiamino  -  triphenyl  -  carbinol,  CetI5  •  C  (OH)  [C6EyST(CH3)2]2. 


484  XXX.   TRIPHENYL-METHANE  GROUP 

The  free  base  is  obtained  by  precipitating  the  salts  with  alkali. 
It  crystallizes  in  colourless  needles  and  dissolves  in  cold  acid 
to  a  colourless  solution;  upon  warming,  however,  the  intense 
green  coloration  of  the  salts  is  produced.  (For  an  explana- 
tion of  this,  see  p.  486.) 

The  double  salt  with  zinc  chloride,  ((X3H25N2C1)3,  2ZnCl2, 
2  H2O,  or  the  oxalate,  (C23H25N2)2,  3  H2C2O4,  of  this  base  is  the 
valuable  dye  bitter-almond-oil  green,  malachite  green  or  Victoria 
green,  which  forms  green  plates,  readily  soluble  in  water.  This 
can  also  be  prepared  directly  by  heating  benzo-trichloride  with 
dimethyl-aniline  and  zinc  chloride  (Doebner).  Brilliant  green 
is  the  corresponding  tetraethyl  compound. 

The  sulphonic  acid  of  the  diethyl-dibenzyl-diamino-triphenyl- 
carbinol  is  acid  green. 

2.  ROSANILINE  GROUP 

Fuchsine  or  magenta  was  first  obtained  in  1856  by  Natanson, 
who  noticed  the  formation  of  a  red  substance,  in  addition  to 
that  of  aniline  hydrochloride  and  ethylene-aniline,  when  ethy- 
lene  chloride  was  allowed  to  act  upon  aniline  at  a  temperature 
of  200°  (A.  98,  297).  It  was  prepared  shortly  afterwards  by  A. 
W.  Hofmann,  by  the  action  of  carbon  tetrachloride  upon  aniline, 
and  was  first  manufactured  on  the  technical  scale  in  1859.  Hof- 
mann's  scientific  researches  on  this  subject  date  from  1861.  The 
chemical  constitution  was  made  clear  by  Emit  and  Otto  Fischer 
in  1878  (A.  194,  242).  (Of.  also  Caro  and  Grabs,  B.  11,  1116.) 

The  rosaniline  dyes  are  derived  partly  from  triphenyl- 
methane  and  partly  from  wi-tolyl-diphenyl-methane;  in  the 
former  case  they  are  often  designated  para-compounds  (e.g. 
"para-rosaniline",  because  it  is  prepared  from  aniline  and  para- 
toluidine ;  "  para-rosolic  acid  "). 

Para-leucaniline,  triamino-triphenyl-methane,  CH(CLH4'NH2)3, 
andleucaniline,  triamino-diplienyl-tolyl-'methane,  CH3  •  C6H3(NH2)  • 
CH(CgH4»NH2)2,  are  formed  by  the  reduction  of  the  corre- 
sponding trinitro- compounds  and  also  of  the  corresponding 
dye-bases,  para-rosaniline  and  rosaniline;  the  first  named  like- 
wise by  the  reduction  of  ^-nitro-diamino-triphenyl-methane. 
The  free  leuco-bases  are  precipitated  by  ammonia  from  solutions 
of  their  salts  as  white  or  reddish  flocculent  masses,  and  crystal- 
lize in  colourless  needles  or  plates;  they  melt  at  203°  and  100° 
respectively.  As  triacid  bases  they  form  colourless  crystalline 
salts. 


PARA-ROSANILINE  AND  ROSANILINE  485 

Para-rosaniline,   OH •  C(C6H4NH2)3,   and  rosaniline,  OH- 
N  xr2R  »  are  the  bases  of  the  fuchsine  dyes.     They 

•  IN  -0-2 

are  obtained  by  precipitating  solutions  of  their  salts  with 
alkalis,  and  crystallize  from  hot  water  or  alcohol  in  colourless 
needles  or  plates,  which  become  red  in  the  air.  Both  are  tri- 
acid  bases,  stronger  than  ammonia.  As  they  yield  tri-diazonium 
salts  on  treatment  with  nitrous  acid,  they  must  contain  three 
primary  amino- groups.  The  diazonium  compounds  readily 
yield  the  corresponding  hydroxylic  dyes,  aurine  and  rosolic 
acid  (p.  490),  when  boiled  with  water. 

Constitution. — The  relations  between  the  rosanilines  and  tri- 
phenyl-methane  were  made  clear  by  Emil  and  Otto  Fischer,  who 
transformed  leucaniline  into  diphenyl-tolyl-methane  by  diazo- 
tizing  and  decomposing  with  alcohol.  In  a  similar  manner, 
para-leucaniline  was  converted  into  triphenyl-methane.  The 
two  leuco-bases  are,  therefore,  undoubtedly  triamino-derivatives 
of  diphenyl-^-tolyl-methane  and  of  triphenyl-methane  respec- 
tively. The  dye-bases,  which  differ  from  the  leuco-bases  by 
one  atom  of  oxygen,  are  the  corresponding  carbinol  derivatives, 
i.e.  rosaniline  is  triamino-diphenyl-^-tolyl-carbinol,  and  para- 
rosaniline  triamino-triphenyl-carbinol. 

That  the  three  amino-groups  are  distributed  equally  among 
the  three  benzene  nuclei  is  clear  from  the  synthesis  of  para- 
leucaniline  by  means  of  ^-nitro-benzaldehyde.  ^?-Nitro-ben- 
zaldehyde,  aniline,  and  sulphuric  acid  yield  ^-nitro-diamino- 
triphenyl-methane,  N02  •  C6H4  •  CH(C6H4  •  NH2)2,  which,  when 
reduced,  yields  para-leucaniline.  We  have,  therefore,  the 
following  formulas : 

5H4.NH2  yC6H4.NH2 

8H4.NH2  C(OH)^C6H4.NH2 
8H4  •  NH2  \C6H3(CH3)  •  NH2 

Para-leucaniline.  Rosaniline. 

It  can  be  shown  that  each  amino -group  occupies  the  p- 
position  with  respect  to  the  methane  carbon  atom.  Diamino- 
triphenyl-methane  can  be  synthesized  from  benzaldehyde  and 
aniline  in  the  presence  of  a  dehydrating  agent.  When 
diazotized  and  warmed  with  water,  the  corresponding  dihy- 
droxy-triphenyl-methane  is  formed,  and  this,  when  fused  with 
potash,  yields  ^-dihydroxy-benzophenone : 
C6H6.CH(C6H4NH2)2  —  C6H6.CH(C6H4.OH)2  —  CO(C6H4.OH)2 

in  this  last  compound  the  ^-positions  of  the  hydroxy-groupa 


486  XXX.   TRIPHENYL-METHANE  GROU? 

have  been  established,  and  hence  the  original  ammo-groups 
must  also  have  occupied  the  p-positions,  unless  intramolecular 
rearrangement  has  occurred. 

When^-nitro-benzaldehyde  is  condensed  with  aniline,  ^-nitro- 
diamino-triphenyl-methane  is  formed,  and  the  nitro-group  must 
be  in  the  ^-position,  and  by  analogy  with  the  previous  reaction 
the  two  amino-groups  are  also  in  ^-positions,  and  as  this  com- 
pound on  reduction  yields  para-leucaniline  it  follows  that  all 
three  amino-groups  occupy  ^-positions  —  a  conclusion  which  is 
supported  by  the  fact  that  para-leucaniline  can  also  be  trans- 
formed into  jp-dihydroxy-benzophenone. 

The  salts  of  rosaniline  and  para  -  rosaniline,  fuchsine, 
C20H20N3C1,  rosaniline  nitrate,  C20H20N3(N03),  rosaniline 
acetate,  C20H2?N3(C2H302),  para-fuchsine,  C19H18N3C1,  &c., 
are  the  actual  dyes.  While  they  possess  a  magnificent 
fuchsine-red  colour  in  solution,  and  have  intense  colouring 
power  (dyeing  wool  and  silk  without  a  mordant),  their  crys- 
tals are  of  a  brilliant  metallic  green  with  cantharides  lustre, 
i.e.  of  nearly  the  complementary  colour.  They  are  fairly 
soluble  in  hot  water  and  alcohol. 

In  the  formation  of  the  salts,  water  is  eliminated: 
qOH)(C6H4.NH2)3  +  HCl  =  C19H17N3,  HC1  +  H20. 


In  the  dyes  there  is  therefore  present  a  peculiar  nitrogen- 
carbon  linking  (see  formula  I),  which  is  reminiscent  of  the 
older  quinone  formula;  but  the  simpler  constitution  (formula 
II),  which  corresponds  with  the  newer  quinone  formula,  is  now 
more  generally  accepted,  and  is  usually  termed  the  quinonoid 
formula  : 

(I)  (II)        C(C6H4NH2)2 

•NH2  /C6H4-NH2 

}H4.NH2  C£-C,H  -NH2 

4.NH,HC1  XVH4:NH,HC1    or 

(Fischer)  (Nietzki) 

•f<.  Para-rosaniline  chloride.  NH2C1 

An  analogous  separation  of  water  is  also  observed  in  the 
formation  of  salts  of  the  malachite  green  base,  but  this  only 
takes  place  upon  warming,  as  is  proved  by  the  fact  that  it 
dissolves  without  colour  in  cold  acids,  and  that  the  intense 
coloration  of  the  salts  first  becomes  apparent  after  warming 
the  solution. 

In  addition  to  the  above  salts  there  also  exist  acid  ones, 
e.g.  C20H20N8C1  +  3HC1  (which  yields  a  yellow-brown  solution, 


FUCHSINE  AND  PARA-FUCHSINE  487 

not  a  fuchsine-coloured  one);  these  dissociate  into  the  neutral 
salts  and  free  acid  upon  the  addition  of  much  water.  The 
formation  of  such  acid  salts  is  readily  accounted  for  by  the 
quinonoid  formula. 

Rosenstiel  has  suggested  the  constitution  Cl  •  C(C6H4NH2)3 
for  para-fuchsine,  according  to  which  the  salt  is  the  chloride 
(ester)  of  a  tertiary  alcohol.  Such  a  constitution,  according 
to  Hantzsch  and  Osswald  (B.  1900,  33,  278),  is  not  in  harmony 
with  known  facts. 

Assuming  the  quinonoid  structure  II  for  para-fuchsine,  then 
the  conversion  into  para-rosaniline  under  the  influence  of 
alkalis  should  be  preceded  by  the  formation  of  an  unstable 
quaternary  ammonium  hydroxide,  which  becomes  transformed 
into  the  carbinol  compound,  para-rosaniline: 

C(C6H4NH2)2  C(C6H4NH2)2 


NH2C1  NH2-OH 

Para-fuchsine.  Para-rosaniline. 

Hantzsch  and  Osswald,  by  means  of  electrical  conductivity 
determinations  (B.  1900,  33,  278),  have  been  able  to  indicate 
the  presence  of  such  an  ammonium  derivative  in  the  solution 
which  is  formed  when  the  dye  is  brought  into  contact  with  an 
equivalent  of  alkali.  This  compound  is  coloured  in  contra- 
distinction to  the  carbinol  base,  is  very  strongly  basic  and 
therefore  strongly  ionized,  and  is  gradually  transformed  into 
the  insoluble  carbinol  base.  Para-rosaniline  and  the  dye-bases 
generally  are  pseudo-bases  corresponding  in  many  respects  with 
the  pseudo-acids  (p.  363). 

Formerly  in  the  manufacture  of  magenta,  a  mixture  of  ani- 
line with  o-  and  ^?-toluidine  was  oxidized  by  syrupy  arsenic 
acid,  stannic  chloride  or  mercuric  chloride  or  nitrate,  &c.;  in 
the  modern  method,  a  mixture  of  nitro-benzene  with  aniline 
and  toluidine  is  heated  with  iron  filings  and  hydrochloric 
acid  (Coupler).  Nitro-toluene  may  also  be  employed  instead 
of  nitro-benzene.  If  o-toluidine  is  present  in  the  mixture  of 
aniline  and  ^?-toluidine  to  be  oxidized,  rosaniline  is  formed, 
and  if  it  is  absent,  para-rosaniline.  When  pure  aniline  is  oxid- 
ized alone,  it  yields  no  fuchsine  at  all,  but  products  of  the 
nature  of  indulin.  This  is  explained  by  the  fact  that  for  the 


488  XXX.   TRIPHENYL-METHANE  GROUP 

formation  of  fuchsine  a  carbon  atom  is  required  which  shall 
serve  to  link  the  benzene  nuclei  together,  a  so-called  "  methane- 
carbon";  in  the  action  of  carbon  tetrachloride  upon  aniline, 
this  carbon  originates  from  the  tetrachloride,  and  in  the  oxi- 
dation of  a  mixture  of  aniline  and  ^-toluidine,  from  the  methyl 
group  of  the  latter,  as  is  shown  in  the  following  scheme  : 


Para-rosaniline  and  rosaniline  are  also  formed  by  heating  p- 
diamino-diphenyl-methane  (p.  476)  with  aniline  and  o-toluidine 
respectively,  in  presence  of  an  oxidizing  agent  (B.  25,  302). 

When  rosaniline  is  heated  with  hydrochloric  or  hydriodic 
acid  to  200°,  it  is  split  up  into  aniline  and  toluidines;  when 
superheated  with  water,  para-rosaniline  yields  jp-dihydroxy-ben- 
zophenone,  ammonia,  and  phenol.  When  boiled  with  hydro- 
chloric acid,  rosaniline  breaks  up  into  ^>-diamino-benzophenone 
and  0-toluidine  (B.  16,  1928;  19,  107;  22,  988).  A  solution 
of  fuchsine  is  decolorized  by  sulphurous  acid,  an  additive- 
product,  fuchsine-sulphurous  acid,  being  formed.  This  solution, 
Schiff's  reagent,  is  a  delicate  reagent  for  aldehydes,  which 
colour  it  violet-red  (see  p.  127;  B.  21,  Kef.  149,  &c.). 

Derivatives  of  Rosaniline 

1.  Methylated  rosanilines  (Hofmann,  Lauth).  —  The  red 
colour  of  para-rosaniline  and  of  rosaniline  is  changed  into 
violet  by  the  entrance  of  methyl  or  ethyl  groups,  the  intensity 
of  the  latter  colour  increasing  with  an  increasing  number  of 
these  groups.  The  salts  of  hexamethyl-para-rosaniline  have 
a  magnificent  bluish-violet  shade.  In  the  manufacture  of  these 
"methyl-violets"  one  may  either  (1)  methylate  rosaniline  (by 
means  of  CH3C1  or  CH3I);  or  (2)  oxidize,  instead  of  aniline, 
a  methylated  aniline  such  as  dimethyl-aniline  by  means  of 
cupric  salts,  whereby  para-rosaniline  derivatives  result;  or  (3) 
allow  phosgene  to  act  upon  dimethyl-aniline  (or  the  latter  to 
act  upon  the  tetramethyl-diamino-benzophenone  at  first  pro- 
duced) (cf.  B.  17,  Kef.  339): 

COC12  +  3C6H6.N(CH3)2  =  C(OHXC6H4.N(CH3)2]3-f2HCl. 

In  the  last  case  hexamethyl-violet,  termed  "  crystal  violet  " 
on  account  of  the  beauty  of  its  crystals,  is  formed,  while  the 


HOSANILINE  DERIVATIVES  489 

hiethyl-  violets  prepared  by  methods  (1)  and  (2)  are  mixtures  of 
hexa-,  penta-,  and  tetramethyl-rosanilines  and  are  amorphous. 

The  hydrochloride  of  the  hexamethyl  dye  has  the  consti- 
tution : 


An  interesting  synthesis  of  this  compound  is  by  the  action  of 
the  magnesium  derivative  of  ^-bromo-dimethyl-aniline  on  tetra- 
methyl-diamino-benzophenone  and  subsequent  treatment  with 
hydrochloric  acid  (cf.  Synthesis  of  Tertiary  Alcohols,  p.  356). 

The  hexamethyl  -  carbinol  no  longer  contains  an  amino- 
hydrogen  atom,  in  consequence  of  which  any  further  methyl 
chloride  or  iodide  cannot  effect  an  exchange  of  hydrogen  for 
alkyl,  but  can  only  form  an  additive  compound,  a  quaternary 
ammonium  salt.  Such  addition  causes  a  change  of  colour  from 
violet  to  green;  thus  the  compound 


is  the  dye  methyl  green  or  light  green.  Ethyl  green  (ethyl- 
hexamethyl  rosaniline)  is  formed  by  the  action  of  ethyl  bro- 
mide on  methyl  violet. 

Various  ethyl  violets  are  known  corresponding  with  the 
methyl  violets.  The  hexa-substituted  rosanilines,  which  con- 
tain benzyl  as  well  as  methyl  or  ethyl  groups,  are  similar  to 
crystal  violet;  their  sulphonic  acids  form  useful  dyes,  e.g.  acid 
violet. 

2.  Phenylated  rosanilines.  By  the  successive  entrance  of 
phenyl-groups  into  rosaniline,  there  are  formed  in  the  first 
instance  violet  dyes,  which  change  to  blue  when  three  phenyl 
groups  have  entered.  Triphenyl-fuchsine  or  "aniline  blue" 
is  a  beautiful  blue  dye,  insoluble  in  water  but  soluble  in 
alcohol.  It  is  prepared  by  heating  rosaniline  with  aniline  in 
presence  of  benzoic  acid,  when  ammonia  is  eliminated;  or  by 
the  oxidation  of  phenylated  aniline,  i.e.  diphenylamine,  e.g.  by 
means  of  oxalic  acid.  The  latter  supplies  the  "methane  carbon 
atom",  and  the  beautiful  "diphenylamine  blue"  or  spirit  blue 
which  is  formed  is  a  para-rosaniline  derivative.  Formic  alde- 
hyde can  also  supply  the  methane  carbon  atom. 

Dyes  insoluble  in  water  are  converted  into  soluble  sulphonic 
acids.  Such  acids  are  Nicholson's  blue,  water  blue,  and  light 
blue.  Patent  blue,  new  patent  blue,  are  disulphonic  acids. 


490  XXX.   TRIPHENYL-METHANE  GROUP 


i.  TRIHYDROXY-TRIPHENYL-METHANE, 
OR  THE  AURINE  GROUP 

The  hydroxy-analogues  of  para-rosaniline  and  rosaniline  are 
aurine,  C19HU03,  and  rosolic  acid,  C20H1603: 

(OH  .  C6H4)2C  •  C6H4  •  O      or      (OH  •  C6H4)2  .  C  :  C6H4  :  0 

I  I     Aurine. 

These  likewise  possess  the  dye  character,  but,  instead  of 
being  basic,  they  are  acid  dyes  (phenol  dyes);  they  are  of  far 
less  value  than  the  basic  dyes  which  have  been  already 
described. 

They  are  formed  when  the  diazonium  derivatives  of  para- 
rosaniline  or  rosaniline  are  boiled  with  water  (Caro  and  Wanlc- 
lyn,  1866): 

OH.C(C6H4N2S04H)8  +  3H20  =  OH.C(C6H4.OH)3  +  3N2  +  3HaS04; 
OH.C(C6H,.OH)S  =  (OH.C6H4)2C:C6H4:0  +  HS0. 


The  carbinol  which  must  be  produced  here  in  the  first  instance 
is  incapable  of  existence,  and  loses  water.  The  constitutional 
formulae  just  given  follow  from  this  close  relation  to  the  rosani- 
lines. 

Aurine  is  also  obtained  by  heating  phenol  with  oxalic  and 
sulphuric  acids  to  130°-150°  (Kolbe  and  Schmitt,  1859),  ,the 
oxalic  acid  yielding  the  "  methane  carbon  atom  "  ;  rosolic  acid 
results  in  an  analogous  manner  from  a  mixture  of  phenol  and 
cresol  with  arsenic  and  sulphuric  acids.  Phenol  by  itself  yields 
no  rosolic  acid  upon  oxidation. 

Aurine  and  rosolic  acid  crystallize  in  beautiful  green  needles 
or  prisms  with  a  metallic  lustre,  dissolve  in  alkalis  with  a 
fuchsine-red  colour,  and  are  thrown  down  again  from  this 
solution  by  acids.  The  alkaline  salts  are  decidedly  unstable, 
aurine  being  but  a  weak  phenol;  at  the  same  time  it  possesses 
a  slightly  basic  character.  An  ammonium  salt  is  known 
which  crystallizes  in  dark-red  needles  with  a  blue  lustre. 
Upon  reduction  there  are  formed  the  leuco-  compounds  leu- 
caurine,  CH(C6H4-OH)3,  and  leuco-rosolic  acid,  OH-C6H3Me. 
CH(C6H4»OH)2,  both  of  which  crystallize  in  colourless  needles 
of  phenolic  character.  Superheating  with  water  transforms 
aurine  into  ^-dihydroxy-benzophenone,  CO(C6H4  •  OH)2,  and 
phenol;  superheating  with  ammonia,  into  para-rosaniline. 


1»HTH  ALOPHENONE  491 


4.  tmPHENYL-METHANE-CARBOXYLIC-ACID,  OB  THE 
EOSIN  GROUP 

(Of.  Eaeyer,  A.  183,  1;  202,  36) 

Triphenyl-methane-carboxylic  acid,  CH(C6H5)2(C6H4.C02H), 
obtained  by  the  reduction  of  phthalophenone  (see  below),  crys- 
tallizes in  colourless  needles  melting  at  162°  and  yields  tri- 
phenyl-methane  by  the  elimination  of  carbon  dioxide. 

Triphenyl-carbinol-o-carboxylic  acid,  OH.C(C6H5)2(C6H4. 
C02H).  The  anhydride  of  this  acid,  which  is  termed  phtha- 
lophenone, is  obtained  by  heating  phthalyl  chloride  with 
benzene  and  aluminic  chloride  (A.  202,  50),  and  forms  plates, 
melting  at  115°.  The  acid  itself  is  incapable  of  existence,  but 
its  salts  are  obtained  by  dissolving  the  anhydride  in  alkalis. 
Phthalophenone  is  on  the  one  hand  a  triphenyl-methane  de- 
rivative and  on  the  other  a  derivative  of  phthalic  acid;  in 
accordance  with  the  constitutional  formula: 


it  is  to  be  regarded  as  diphenyl-phthalide  (Phthalide,  p.  462). 
Phthalophenone  is  the  mother  substance  of  a  large  series 
of  dyes,  which  are  derived  from  it  by  the  entrance  either  of 
hydroxyl  or  of  amino-groups.  They  are  prepared  by  the  action 
of  phenols  upon  phthalic  anhydride,  and  are  termed  Phthaleins. 
Phenol  and  resorcinol,  for  example,  yield  the  compounds  : 


and 


Phenol-phthalem  Fluorescem. 

Quinonoid  formulae  are  also  possible,  e.g.  for  phenol-phthalein, 


Free  phenol-phthalein,  which  is  colourless,  probably  has  the 
lactone  formula,  and  its  coloured  salts  the  quinonoid  structure. 
Phenol-phthalein  would  then  be  a  pseudo-acid  (p.  364). 

See  also  H.  Meyer,  M.  1899,  20,  337;  R.  Meyer  and  Spendkr, 

B.  36,  2949;  38,  1318;  Green  and  A.  G.  Perkin,  3.  C.  S.  1904, 
398;  Green  and  King,  B.  39,  2365;  40,  3724;  Stieglite,  J.  A. 

C.  S.  25,  1112;  Acree,  Am.  C.  J.  39,  528,  771;  425  115. 


492  XXX.    TRIPHENYp-METHANE  GROUP 

In  the  case  of  fluorescein  a  molecule  of  water  is  split  off 
from  two  hydroxyls  of  the  two  resorcinol  residues.  Phthaleins 
of  this  kind  (being  hydroxy-phthalophenones)  are  converted  by 
reduction  into  the  hydroxy-derivatives  of  triphenyl-methane- 
carboxylic  acid,  which  are  termed  "Phthalines";  e.g.  phenol- 
phthalein  into  dihydroxy-triphenyl- methane -carboxy lie  acid 

(C  H  «OH) 
(i.e.  phenol-phthaline),  CH^n  H  t TO  H'     ^e  phthalines  are 

Vxg-L-*-^      V/Vyg-*-*- 

colourless,  and  are  to  be  looked  upon  as  leuco-compounds  of 
the  phthaleins.  The  phthaleins  include  among  themselves 
many  dyes  which  are  of  technical  value,  e.g.  the  eosins  (Caro, 
Baeyer,  1871). 

Phenol-phthalei'n  is  prepared  by  heating  phthalic  anhydride 
with  phenol  and  sulphuric  acid,  or  better,  stannic  chloride  (or 
oxalic  acid),  to  115°-120°.  It  may  also  be  obtained  by  nitrating 
diphenyl-phthalide,  reducing  the  two  substituting  nitro-groups, 
and  replacing  the  amino-groups  thus  formed  by  hydroxyl  in 
the  usual  manner  (A.  202,  68).  It  crystallizes  from  alcohol  in 
colourless  crusts;  is  nearly  insoluble  in  water,  but  dissolves 
in  dilute  alkalis  with  a  beautiful  red  colour  which  vanishes 
again  on  neutralization  with  acids;  it  is  thus  a  valuable  indi- 
cator. With  very  concentrated  alkalis  (KOH)  phenol-phthalein 
yields  colourless  solutions  probably  containing  metallic  salts  of 
a  non-quinonoid  structure.  The  ^-positions  of  the  two  hydroxy- 
groups  have  been  proved  by  conversion  into  ^-dihydroxy- 
benzophenone.  It  yields  a  di-acetyl  derivative  melting  at  143° 
and  an  oxime  melting  at  212°.  It  is  reduced  by  potash  and 
zinc  dust  to  phenol-phthaline  (colourless  needles),  which  dis- 
solves in  alkalfto  a  colourless  solution,  but  is  readily  reoxidized 
in  this  solution  to  phenol-phthalein. 

Fluorane,  C20H1203,  which  was  formerly  regarded  as  phenol- 
phthalein  anhydride,  is  formed  as  a  by-product  in  the  phenol- 
phthalein  melt,  and  is  the  mother  substance  of  fluorescein. 
Both  probably  contain  a  pyrone  ring  (and  hence  the  name 
Pyronines  for  the  whole  group  of  dyes),  and  the  constitution 
of  fluorane  is  represented  as 

Fluorane,  ^         ^> — C 
CO-0 

(Cf.  R.  Meyer,  B.  1892,  25,  1385,  2118;  1893,  26,  1271.) 


FLUORESCEIN  493 

Fluorescei'n,  Dikydroxy-fluorane  orresarcinol-phlhakw,  C20H1205 
•f  H20,  is  prepared  by  heating  phthalic  anhydride  and  resor- 
cinol  at  200°.  It  forms  a  dark-red  crystalline  powder,  and  dis- 
solves in  alcohol  with  a  yellow-red  colour,  and  in  alkalis  with 
a  red  colour  and  splendid  green  fluorescence.  It  is  reducible 
to  the  phthaline  "  Fluorescin ",  and  with  bromine  yields  red 
crystals  of  tetrabromo-fluorescein,  the  potassium  salt  of  which, 
C20H(.Br406K2,  is  the  magnificent  dye  eosin.  Fluorescing  dyes 
are  likewise  formed  in  an  analogous  manner  from  all  the  de- 
rivatives of  1 : 3-dihydroxy-benzene,  in  which  position  5  is  un- 
occupied, and  the  reaction  is  often  made  use  of  on  the  one 
hand  for  testing  for  ra-dihydroxy-derivatives,  and  on  the  other 
for  phthalic  anhydride  or  succinic  anhydride. 

Instead  of  phthalic  acid  itself,  chlorinated  or  brominated, 
&c.,  phthalic  acids  may  be  employed,  so  that,  by  gradually 
increasing  the  amount  of  halogen  present,  a  whole  series  of 
yellow-red  to  violet-red  eosins  can  be  prepared,  e.g.  tetrabromo- 
di-iodo-eosin;  these  are  known  under  the  names  of  Erythrosin, 
Eose  de  Bengale,  Phloxin,  &c.  It  is  worthy  of  note  that  many 
other  dibasic  acids  (e.g.  succinic)  and  also  benzoic  acid  are 
capable  of  yielding  nuorescing  compounds. 

Gallein,  C20H].,O7,  is  the  dye  obtained  from  pyrogallol  and 
phthalic  anhydride. 

The  rhodamines  are  dyes  closely  allied  to  fluorescein.  They 
are  obtained  by  the  condensation  of  phthalic  anhydride  and 
^-alkylated-amino-phenols  in  presence  of  sulphuric  acid.  They 
contain  the  pyrone  ring,  and  may  be  regarded  as  fluorescein 
in  which  the  two  hydroxyl  groups  have  been  replaced  by 
tertiary  amino-groups.  Tetra-ethyl  rhodamine, 

6H3-NEt2- 


is  colourless,  and  has  basic  properties.    The  salts,  e.g.  sulphate, 
are  red  dyes,  and  probably  possess  a  quinonoid  structure. 


Tetraphenyl-methane,  C(C6H5)4.— Many  attempts  to  obtain 
this  compound  were  made,  but  without  success,  until  Gomberg 
(B.  1897,  30,  1897)  succeeded  in  preparing  it  from  triphenyl- 
bromo- methane.  With  phenyl-hydrazine  this  yields  CPh3» 
NH.NHPh,  triphenylmethane-hydrazobenzene,  which  gives 
the  corresponding  azo-compound  when  oxidized,  CPh3«N:NPh, 


494  XXXI.   NAPHTHALENE  GROUP 

and  when  this  is  heated  nitrogen  is  evolved  and  tetraphenyl 
methane  is  formed.  It  is  more  readily  prepared  by  the  action 
of  magnesium  phenyl  bromide  on  triphenyl-chloro- methane 
(B.  1906,  39,  1462).  It  forms  colourless  crystals,  m.-pt.  282°. 


XXXI.   COMPOUNDS   WITH   CONDENSED   BENZENE 
NUCLEI.     NAPHTHALENE  GROUP 

The  higher  fractions  of  coal  tar  contain  hydrocarbons  of 
high  molecular  weight,  especially  naphthalene,  C^Hg,  an- 
thracene, C14H10,  and  its  isomeride  phenanthrene.  The  first- 
named  is  found  in  the  fraction  between  180°-200°,  and  the 
two  latter  in  that  between  340°-360°. 

These  compounds  are  of  more  complex  composition  than 
benzene,  the  molecule  of  naphthalene  differing  from  that  of 
the  latter  by  C4H2,  and  those  of  anthracene  and  phenanthrene 
from  that  of  naphthalene  by  the  same  increment.  They 
closely  resemble  benzene  as  regards  behaviour,  and  give  rise 
to  types  of  derivatives  similar  to  those  of  benzene  itself. 

They  undoubtedly  contain  benzene  nuclei,  as  anthracene 
yields  benzoic  acid  upon  oxidation,  naphthalene  phthalic  acid, 
and  phenanthrene  diphenic  acid.  From  their  modes  of  forma- 
tion and  behaviour  it  follows  that  in  the  building  up  of  their 
molecules  the  benzene  residues  combine  together  in  such  a 
manner  that  2  or  (2  x  2)  adjacent  carbon  atoms  are  common 
to  both  (cf.  pp.  496  and  506). 

NAPHTHALENE  GROUP 

Naphthalene,  C10H8,  was  discovered  by  Garden  in  1820. 
It  is  contained  in  coal-tar  and  crystallizes  from  the  fraction 
which  distils  over  between  180°-200°.  These  crystals  are 
pressed  to  free  them  from  oily  impurities,  and  can  then  be 
further  purified  by  treatment  with  small  amounts  of  con- 
centrated sulphuric  acid  and  subsequent  sublimation. 

It  is  also  formed  when  various  carbon  compounds  are  sub- 
jected to  a  red  heat;  thus,  •  together  with  benzene,  styrene, 
&c.,  by  passing  the  vapours  of  methane,  ethylene,  acetylene, 
alcohol,  acetic  acid,  &c.,  through  red-hot  tubes.  Its  presence 
in  coal-tar  may  be  due  to  some  similar  cause. 

The  constitutional  formula  (p.  496)  is  largely  based  on  the 
following  syntheses: — 


NAPHTHALENE  GROUP  495 

1.  By  the  action  of  0-xylylene  bromide  upon  the  sodium 
compound  of   the   symmetrical   ethane  -tetracarboxy  lie  ester, 
ethyl  tetrahydronaphthalene-tetracarboxylate  is  formed: 
r      Na.C(C02Et)2  ,CH2.C(CO2Et)2 


and  from  this,  naphthalene  may  be  obtained  by  hydrolysis, 
the  elimination  of  the  carboxyl  groups  and  subsequent  oxi- 
dation (Baeyer  and  Perkin,  B.  17,  448). 

2.  a-Naphthol,  C^H^-OH,  is  produced  by  the  elimination 
of  water  from  y-phenyl-isocrotonic  acid  (Fittig  and  Erdmann, 
B.  16,  43;  see  p.  456),  and  yields  naphthalene  when  heated 
with  zinc  dust. 

3.  J.  F.  Thorpe  (P.  1905,  21,  305)  has  succeeded  in  syn- 
thesising  a  number  of  naphthalene  derivatives  by  means  of 
ethyl  sodio-cyano-acetate,  e.g.  ethyl  1  :  3-diamino-naphthalene-2- 
carboxylate  from  ethyl  sodio-cyano-acetate  and  benzyl  cyanide. 

C6H6  •  CH2  •  ON  +  CO2Et  •  CH2  -  CN 

—  C6H5.CH2.C(:NH).CH(C02Et)CN, 

and  this  with  sulphuric  acid  yields  the  bicyclic  compound  I, 
which  is  immediately  transformed  into  the  diamino-deriva- 
tive  II. 

CH2 


CH-COoEt 
:NH 

The  same  compound  may  be  synthesised  from  ethyl  sodio- 
cyano-acetate  by  the  following  stages  (J.  C.  S.  1907,  91,  578). 
Condensed  with  o-toluyl  chloride,  CH3«C6H4^CO'C1,  it  yields 
ethyl  cyano-0-toluyl-acetate,  CH3  -  C6H4  •  CO  •  CH(CN)C02Et, 
and  this  when  heated  with  ammonium  acetate  gives  the  corre- 
sponding imino-derivative,  CH3  •  C^  •  C(  :  NH)  •  CH(CN)C02Et, 
ethyl  /3-imino-a-cyano-/3-o-tolyl-propionate,  which  reacts  with 
acids  giving  compound  I. 

l:4-Naphthalene-diamines  have  been  prepared  by  similar 
methods,  using  derivatives  of  phenyl-butyric  acid  (J.  C.  S. 
1907,  91,  1004). 

Constitution.  —  That  naphthalene  contains  a  benzene  nucleus, 
in  which  two  hydrogen  atoms  occupying  the  ortho-  position 
are  replaced  by  the  group  (C4H4)",  follows  not  only  from  its 
oxidation  to  phthalic  acid,  but  also  from  its  formation  from 


496  XXXI.   NAPHTHALENE  GROUP 

0-xylylene  bromide.  And  that  the  four  carbon  atoms  of  this 
group  are  linked  to  one  another  without  branching  is  shown 
by  the  formation  of  a-naphthol. 

CH 


CO 

'  TT  a-Naphthol. 

•y-Phenyl-iso-crotonic  acid 

That  there  are  actually  two  so-called  "  condensed  "  benzene 
nuclei  present  in  the  naphthalene  molecule  is  a  necessary  con- 
sequence of  the  fact  that  phthalic  acid  or  its  derivatives  ensue 
on  the  breaking  up  of  the  compound,  not  only  from  one  but 
from  both  of  the  rings. 

For  instance,  a-nitro-naphthalene  (p.  499)  on  oxidation  yields 
nitro-phthalic  acid,  C6H3(NO2)(C02H)2;  consequently  the  ben- 
zene ring  to  which  the  nitro-group  is  linked  remains  intact. 
But,  on  reducing  the  nitro-naphthalene  to  amino-naphthalene 
and  oxidizing  the  latter,  no  amino-phthalic  acid  nor  any  oxi- 
dation product  of  it  is  obtained,  but  phthalic  acid  itself,  a  proof 
that  this  time  the  benzene  nucleus  to  which  the  amino-group  is 
attached  has  been  destroyed,  and  that  the  other  has  remained 
intact  (Graebe,  1880;  for  an  analogous  proof  by  him,  see 
A.  149,  20). 

Naphthalene  therefore  receives  the  constitutional  formula 
(Erlenmeyer,  1866): 

H 

//^  /^ 
H 


H 


There  is  the  same  difficulty  in  deciding  between  the  double 
bond  KekuU  formula  and  the  centric  formula  as  in  the  case  of 
benzene. 

The  above  constitutional  formula  is  in  complete  harmony 
with  the  number  of  isomeric  forms  in  which  naphthalene 
derivatives  occur,  and  also  with  the  formation  of  additive 
compounds  with  hydrogen  or  chlorine.  (Cf.  Bamberger^  A, 
357,  1;  B.  1891,  24,  2054.) 


NAPHTHALENE  497 

This  union  of  two  benzene  nuclei  is  accompanied  by  a 
modification  of  their  properties,  so  that  naphthalene  and  its 
derivatives  differ  characteristically  from  benzene  in  many 
respects.  Such  differences  show  themselves,  for  instance, 
between  the  naphthylamines  and  aniline,  the  naphthols  and 
phenol;  and  also  especially  in  the  greater  readiness  with 
which  the  naphthalene  derivatives  are  reduced,  the  latter 
taking  up  as  many  as  four  atoms  of  hydrogen  easily. 

After  such  addition  the  reduced  nucleus  is  found  to  have 
entirely  lost  the  characteristics  of  a  benzene  nucleus,  and  to 
have  become  similar  in  properties  to  an  alphyl  radical,  whereas 
the  non-reduced  nucleus  assumes  the  character  of  a  benzene 
nucleus  in  its  entirety  (Bamberger).  (See  the  Tetrahydro-deriva- 
tives  of  the  Naphthylamines  and  Naphthols,  pp.  500  and  502.) 

Properties. — Naphthalene  crystallizes  in  glistening  plates,  is 
insoluble  in  water,  sparingly  soluble  in  cold  alcohol  and  ligroin, 
but  dissolves  readily  in  hot  alcohol  and  ether;  it  melts  at  80° 
and  boils  at  218°.  It  has  a  characteristic  tarry  smell,  and  is 
distinguished  by  the  ease  with  which  it  sublimes  and  volatilizes 
with  steam. 

With  picric  acid  it  yields  an  additive  compound,  C10H8, 
OH  •  CgH2(N02)3,  crystallizing  in  yellow  needles  and  melting 
at  149  .  It  takes  up  hydrogen  far  more  readily  than  benzene 
does,  yielding  di-  and  tetrahydronaphthalenes,  C10Hp  and 
C10H12;  both  of  these  are  liquids  of  pungent  odour  which  re- 
generate naphthalene  again  when  heated.  By  the  powerful 
action  of  hydriodic  acid  and  phosphorus,  the  second  benzene 
nucleus  can  also  be  made  to  take  up  hydrogen,  so  that  a  hexa- 
hydro-,  Q,0H14,  and  finally  a  dekahydronaphthalene,  C10H18,  are 
formed.  It  also  yields  additive  products  with  chlorine  more 
readily  than  benzene  does,  e.g.  naphthalene  dichloride,  C10H8« 
C12,  and  -tetrachloride,  C10H8-C14  (m.-pt.  182°);  the  latter  is  oxi- 
dized to  phthalic  acid  more  easily  than  naphthalene  itself,  hence 
that  acid  is  sometimes  prepared  from  it  on  the  large  scale. 

Naphthalene  is  principally  used  for  the  preparation  of  phthalic 
acid  (for  eosin,  indigo,  &c.),  and  of  naphthylamines  and  naph- 
thols (for  azo-dyes);  also  for  the  carburation  of  illuminating 
gas.  It  is  a  powerful  antiseptic,  and  is  employed  therapeuti- 
cally. 

NAPHTHALENE  DERIVATIVES 

The  number  of  substitution  products  in  the  case  of  naph- 
thalene is  greater  than  with  benzene. 

(B480)  21 


498  XXXI.    NAPHTHALENE  GROUP 

The  mono-derivatives  invariably  exist  in  two  isomeric  forms,  the 
a-  and  ^-compounds,  e.g.: 

C10H7C1  (a-  and  /3-chloro-naphthalene). 
C10H7NH2  (a-  and  jS-naphthylamine). 
C10H7OH  (a-  and  /3-naphthol). 
C10H7CH3  (a-  and  /3-methyl-naphthalene). 

As  in  the  case  of  the  benzene  compounds,  the  existence  of 
two  series  of  mono-derivatives  has  not  only  been  established 
empirically,  but  it  has  also  been  proved  (in  a  manner  similar 
to  that  given  on  p.  329,  et  seq.)  that  in  the  naphthalene  mole- 
cule two  sets  of  hydrogen  atoms  (the  a  and  /?,  a  =  1,  4,  5,  8; 
/3  =  2,  3,  6,  7)  have  an  equal  value  as  regards  one  another, 
but  the  atoms  of  the  one  set  differ  from  those  of  the  other,  so 
that  the  a-  and  the  /3-positions  occur  severally  four  times,  i.e. 
twice  in  each  benzene  nucleus  (Atterberg). 

The  above  constitutional  formula  for  naphthalene  satisfies 
these  conditions,  since,  according  to  it,  the  positions  1,  4,  5, 
and  8  are  severally  equal  and  also  the  positions  2,  3,  6,  and  7, 
but  not  the  positions  1  and  2.  The  conception  that  in  the 
a-compounds  the  position  1,  4,  5,  or  8  is  occupied  is  due  to 
Liebermann  (A.  183,  225),  Eeverdin  and  Noelting  (B.  13,  36), 
and  Fittig  and  Erdmann  (cf.  the  formation  of  a-naphthol  given 
above). 

With  regard  to  the  di-derivatives  of  naphthalene,  a  consider- 
able number  of  isomerides  of  a  good  many  are  known;  accord- 
ing to  the  naphthalene  formula,  ten  are  theoretically  possible  in 
each  case  when  the  two  substituents  are  the  same,  and  fourteen 
when  they  are  different.  The  ten  possible  isomerides  are 
1:2,  1:3,  1:4,  1:5,  1:6,  1:7,  1:8,  2:3,  2:6,  and  2:7.  All  other 
combinations  are  identical  with  one  of  these  ten.  According 
to  Armstrong  and  Wynne  ten  dichloro-  and  fourteen  trichloro- 
naphthalenes  are  actually  known.  (See  also  B.  1900,  33, 1910, 
2131.) 

The  position  1:8  is  termed  the  "peri-"  position;  it  resembles 
the  ortho-  position  to  some  extent,  e.g.  £>m-naphthalene-dicar- 
boxylic  acid  like  an  o-dicarboxylic  acid  yields  an  anhydride. 

The  homologues  of  naphthalene  are  of  comparatively  small 
importance,  and  are  usually  prepared  by  Fittig's  or  by  Friedel 
and  Crafts'  synthesis.  Most  of  them  are  liquids,  and  on  oxi- 
dation yield  acids  resembling  benzoic  acid. 

«-Bromo-naphthalene  can  be  prepared  directly  by  brominat- 
ing  naphthalene,  and  is  partially  converted  into  the  y&-compound 


NAPHTHYLAMINES  499 

when  heated  with  aluminium  chloride.  Its  bromine  atom  is 
somewhat  more  readily  exchangeable  than  that  of  bromo- 
benzene,  but  cannot  be  eliminated  by  boiling  with  alkalis. 
Interesting  methods  of  formation  of  the  halogen  derivatives 
are  by  heating  the  hydroxy-,  nitro-,  or  sulphonic  acid  deriva- 
tives with  phosphorus  pentachloride. 

a-Nitro-naphthalene,  C10H7»N02  (Laurent,  1835),  is  formed 
by  the  direct  nitration  of  naphthalene.  It  crystallizes  in 
yellow  prisms,  melts  at  61°,  boils  without  decomposition,  and 
readily  yields  1 : 5  and  1:8  di-  and  various  tri-  and  tetra-nitro- 
naphthalenes  upon  further  nitration.  On  reduction  it  is  con- 
verted into  a-naphthylamine.  The  position  of  the  nitro-group 
has  been  established  by  conversion  of  this  compound  into  a- 
naphthol. 

The  isomeric  /?-nitro-naphthalene  can  be  obtained  indirectly 
by  diazotizing  /3-naphthylamine,  and  acting  on  the  product  with 
sodium  nitrite  in  presence  of  cuprous  oxide  (B.  20,  1494;  36, 
4157);  it  crystallizes  in  bright  yellow  needles  melting  at  79°. 

a-Naphthylamine,  C10H7«NH2  (Zinin),  forms  colourless 
needles  or  prisms,  melts  at  50°,  boils  at  300°,  and  is  readily 
soluble  in  alcohol.  It  can  be  obtained  by  reducing  the  a-nitro- 
compound,  and  also  readily  by  heating  a-naphthol  with  the 
double  compound  of  calcium  chloride  arid  ammonia,  while 
aniline  can  only  be  prepared  from  phenol  in  a  similar  manner 
with  difficulty:  Ci0H7.OH  +  NH3  =  C10HrNH2  +  H20. 

It  possesses  a  disagreeable  fsecal-like  odour,  sublimes  readily, 
and  turns  brown  in  the  air.  Certain  oxidizing  agents,  such  as 
ferric  chloride,  produce  a  blue  precipitate  with  solutions  of  its 
salts,  while  others  give  rise  to  a  red  oxidation  product;  chromic 
anhydride  oxidizes  it  to  a-naphthaquinone.  In  other  respects 
it  resembles  aniline;  for  differences,  see  B.  23,  1124.  Its  hy- 
drochloride  is  only  sparingly  soluble  in  water. 

The  isomeric  /3-naphthylamine,  C10Hr«NH2  (Liebermann, 
1876),  is  most  conveniently  prepared  by  heating  /?-naphthol 
either  in  a  stream  of  ammonia  or  with  the  double  compound 
of  zinc  chloride  and  ammonia.  It  is  now  generally  prepared  by 
the  action  of  ammonium  hydroxide  and  sulphite  on  /2-naphthol 
(C.  C.  1901, 1,  349).  Naphthyl  ammonium  sulphite  is  formed  as 
an  intermediate  product  and  reacts  with  the  ammonia,  yield- 
ing naphthylamine  and  ammonium  sulphite.  This  reaction  is 
frequently  used  for  transforming  derivatives  of  a  and  ft  naph- 
thol  into  corresponding  amino-compounds.  The  reaction  is 
reversible  and  can  be  used  for  replacing  NH2  by  OH. 


500  XXXI.    NAPHTHALENE   GROUP 

/3-Naphthylamine  crystallizes  in  nacreous  plates,  melts  at 
112°,  boils  at  294°,  and  has  no  odour.  It  is  more  stable  than 
a-naphthylamine,  and  is  not  coloured  by  oxidizing  agents. 

Both  of  these  naphthylamines  can  be  converted  into  tetra- 
hydro-compounds  by  the  action  of  sodium  and  amyl  alcohol 
(i.e.  nascent  hydrogen)  upon  them.  The  tetrahydro-a-naphthyl- 
amine  resembles  its  mother  substance  closely  in  most  of  its 
properties,  e.g.  it  can  be  diazotized  and  has  entirely  assumed 
the  character  of  aniline;  the  hydrogen  atoms  have  entered  the 
nucleus  which  does  not  contain  the  amino-group.  It  is  termed 
aromatic  or  "ar"-tetrahydro-a-naphthylamine.  (Formula  I.) 
Tetrahydro-^-naphthylamine,  on  the  other  hand,  is  not  diazo- 
tized by  nitrous  acid,  but  transformed  into  a  very  stable 
nitrite.  Here  it  is  the  benzene  nucleus  containing  the 
amino-group  which  has  become  reduced;  the  compound  has 
assumed  the  properties  of  an  amine  of  the  fatty  series,  and 
is  termed  alicydic  or  "ac"-tetrahydro-/3-naphthylamine. 
(Formula  II.)  The  a-compound  is  oxidizable  to  adipic  acid 
(p.  231),  and  the  ^-compound  to  o-hydrocinnamo-carboxylic 

acid,  C6H4<^2^CH2'C02H.     (Cf.  Bamlerger  and  others,  B. 
21,  847, 1112,  1892;  22,  625,  767;  23,  876,  1124.) 
H     NH2 

II 
\ 


An  ac-tetrahydro-o-  and  an  ar-tetrahydro-^-naphthylamine 
have  also  been  prepared. 

From  both  naphthylamines  there  are  derived,  as  in  the 
benzene  series,  methyl-  and  dimethyl-naphthylamines,  phenyl- 
a-  and  -/3-naphthylamines  (which  are  of  technical  importance), 
nitro-naphthylamines,  diamino-naphthalenes  or  naphthylene- 
diamines,  C10H6(NH2)2,  diazonium- compounds  (which  are  in 
every  respect  analogous  to  the  diazonium  salts  of  benzene, 
especially  in  the  formation  of  azo-dyes,  many  of  which  are  of 
great  technical  importance),  diazo-amino-compounds,  &c. 

The  diazo-amino-naphthalene,  C10Hr  •  N  :  N  •  NH  •  C10Hr, 
which  is  formed  by  the  action  of  nitrous  acid  upon  a-naphthyl- 
amine, readily  undergoes  a  molecular  transformation  (like  the 
corresponding  benzene  compound)  into  amino-azo-naphthalene, 


NAPHTHALENE  SULPHONIC  ACIDS.      NAPHTHOLS        501 

C10H7  •  N :  N  •  C10H6  •  NH2.  This  latter  compound  crystallizes 
in  brownish-red  needles  with  a  green  metallic  lustre,  and  can 
be  diazotized,  its  diazo-compound  yielding  a-azo-naphthalene, 
CjgHy.NiN'CjoHf  (red  to  steel-blue  glistening  prisms),  when 
boiled  with  alcohol.  This  last  can  either  not  be  prepared  at 
all  or  only  with  great  difficulty  by  the  methods  which  hold 
good  for  azo-benzene. 

A  mixture  of  naphthalene  a-  and  /3-sulphonic  acids,  C10H7  • 
S02  •  OH,  is  obtained  by  warming  naphthalene  to  80°  with  con- 
centrated sulphuric  acid.  They  may  be  separated  by  aid  of 
their  calcic  or  baric  salts,  as  the  /3-sulphonates  are  less  soluble 
than  the  a-salts.  The  a-acid  is  transformed  into  the  /?-acid 
when  heated  with  concentrated  sulphuric  acid,  and  hence  the 
chief  product  obtained  by  sulphonating  naphthalene  at  160° 
is  the  /3-acid.  The  sulphonic  acid  radicals  in  these  compounds 
may  be  readily  replaced  by  hydroxyl  or  cyanogen  by  the  usual 
methods. 

Naphthalene  -disulphonic  acids,  C10H6(SO3H)2. — Two  iso- 
meric  /?-/?-acids  (2:6  and  2:7)  are  formed  when  naphthalene  is 
heated  with  concentrated  sulphuric  acid  at  160°-200°,  while  an 
a-a-acid  (1:5)  is  obtained  with  chloro-sulphonic  acid,  S03HC1, 
in  the  cold,  and  the  a-/?-acid  (1:6)  from  the  /?-mono-sulphonic 
acid  in  a  similar  manner. 

Naphthylaxnine  -  mono  -  sulphonic  acids,  NH2  •  C10H6  •  S02  • 
OH. — Thirteen  isomers  of  these  are  known  (7  a-  and  6  /?-). 
Naphthionic  acid  (NH2 :  S03H  =  1 : 4)  is  obtained  by  the 
sulphonation  of  a-naphthylamine ;  it  is  employed  in  the  pre- 
paration of  azo-dyes,  as  are  also  several  of  its  isomers  and 
various  naphthylamine  -  disulphonic  acids.  These  last  are 
obtained  (a)  directly  from  a-  or  /3-naphthylamine,  or  (b)  by 
nitrating  the  naphthalene-sulphonic  acids  and  then  reducing 
the  nitro-  to  an  amino-group. 

a-  and  /?-Naphthols,  010H7  •  OH,  which  are  present  in  coal-tar, 
can  be  easily  prepared,  not  only  from  the  naphthalene-sulphonic 
acids  as  above,  but  also  by  diazotizing  the  naphthylamines. 
They  crystallize  in  glistening  plates,  have  a  phenolic  odour, 
and  dissolve  readily  in  alcohol  and  ether  but  only  sparingly  in 
hot  water.  a-Naphthol  (Griess,  1866)  melts  at  95°  and  boils 
at  282°,  while  /3-naphthol  (Scha/er,  1869)  melts  at  122°  and 
boils  at  288°;  both  of  them  are  readily  volatile  at  ordinary 
temperatures.  They  possess  a  phenolic  character  but  never- 
theless resemble  the  alcohols  of  the  benzene  series  more  than 
tho  phenols,  their  hydroxy-groups  being  much  more  reactive 


502  XXXI.   NAPBT&ALENE  GROUP 

than  those  of  the  latter,  e.g.  they  can  be  readily  replaced  by 
amino-groups  (see  above).  /?-Naphthol  is  an  antiseptic. 

ar-Tetrahydro-a-naphthol,  C10H7«H4.(OH),  obtained  by 
reducing  a-naphthol,  has  the  character  of  a  pure  phenol,  and 
not  that  of  a-naphthol.  A  mixture  of  ar-  and  ac-  tetrahydro- 
/2-naphthols  is  obtained  from  /8-naphthol,  the  ar-compound 
corresponds  with  phenol  and  the  ac-compound  with  alcohol. 

Ferric  chloride  oxidizes  a-  and  /3-naphthols,  with  production 
of  violet  and  greenish  colorations  respectively,  to  di-naphthols, 
C20H12(OH)2,  which  correspond  with  the  dihydroxy-diphenyls 
(p.  473),  and  are  derivatives  of  di-naphthyls  (p.  504).  The 
cautious  oxidation  of  a-naphthol  yields  o-cinnamo-oarboxylic 
acid,  C02H.C6H4.CH:CH.C02H,  and  that  of  /3-naphthol, 
o-carb'oxy-phenyl-glyoxylic  acid,  C02H .  C6H4  •  CO  •  C02H. 

The  naphthols  yield  alkyl  and  acyl  derivatives.  The  ethers 
are  formed  by  the  action  of  an  alcohol  and  hydrogen  chloride 
on  the  naphthols.  /3-Naphthyl-methyl-ether,  C10Hr-0'CH3, 
is  the  nerolin  used  as  a  perfume. 

From  the  naphthols,  as  from  the  phenols,  there  are  derived 
nitro-,  dinitro-,  trinitro-,  and  amino-compounds,  &c.  The 
calcium  salt  of  dinitro-a-naphthol,  C10H5(N02)2«OH,  is  known 
as  Martins'  yellow  or  naphthalene  yellow,  and  its  sulphonic 
acid,  naphthol  yellow  S  or  fast  yellow,  is  a  valuable  dye. 

Amino  -  naphthols,  C10H6(NH2)(OH),  are  obtained  by  the 
reduction  of  nitro-naphthols;  like  the  amino-phenols  they  are 
readily  oxidized  in  the  air.  (NH2:OH  in  the  a-compound 
=  1:4,  in  the  /^-compound  =  1:2.) 

A  number  of  naphthol-mono-,  -di-,  &c.,  sulphonic  acids  are 
known,  also  amino-naphthol-sulphonic  acids,  which  are  of  great 
technical  value.  Among  these  may  be  mentioned  1 : 4-naph- 
thol-  sulphonic  acid  (Nevile  and  JTinther),  from  naphthionic 
acid,  the  2:8-acid,  the  2:6-acid,  the  /?-naphthol-disulphonic 
acids  E  (2:3:6)  or  "It-salt",  and  G  (2:6:8)  or  "G-salt". 
l-Amino-8-naphthol-3:6-disulphonic  acid  =  H  acid. 

Sodium  l-amino-2-naphthol-6-sulphonate  is  used  as  a  photo- 
graphic developer  under  the  name  of  Eikonogen. 

Azo-dyes. — A  series  of  very  important  azo-dyes  (see  also 
under  Benzidine,  p.  472)  are  produced  by  the  action  of  dia- 
zonium  compounds,  and  of  diazo-naphthalene-snlphonic  acids 
upon  the  naphthylamines  and  naphthols,  and  especially  upon 
the  sulphonic  acids  of  these,  e.g.: 

Benzene-azo-a-naphthylamine,  C6EL  •  N :  N  •  C-,  0H6  •  NH2 ; 

Orange  II,  S08Na.C6H4.N:N.C10H6.OH[/?]; 


NAI»HTHAQUINONES  503 

Ponceau  2R,  from  diazotized  xylidine  and  "E-salt";  Fast 
Red  C  ("EchMh"),  S03Na.C10H6.N:N.C10H5(pH)(S03Na), 
from  naphthionic  acid  and  l-naphthol-4-sulphonic  acid;  Bie- 
brich  Scarlet,  S03Na .  C6H4  -  N :  N .  C6H4 .  N :  N  •  C10H6(OH),  from 
amino-azo-benzene-sulphonic  acid  and  /3-naphthol;  Brilliant 
Black,  (SOsNaJjC^.NiN.Cj^.NrN.O^OHJfSOsNaJa, 
from  naphthylamine-disulphonic  acid,  a-naphthylamine,  and 
"K-salt";  Palatin  Black,  S03Na.C6H4.N2.C10H3(N2C10H7) 
(NH2)(OH)(S03Na),  from  diazobenzenesulphonic  acid,  a-azo- 
naphthalene,  and  l-amino-8-naphthol-4-sulphonic  acid. 

Quinones  of  the  Naphthalene  Series. — Three  isomeric  quin- 
ones,  C10H602,  are  known;  two  correspond  with  para  and 
ortho  benzoquinones. 

a-Naphthaquinone  may  be  obtained  by  the  oxidation  of 
naphthalene,  a-naphthylamine,  l-amino-4-naphthol,  l:4-di- 
hydroxy-naphthalene,  and  of  various  derivatives  of  naphtha- 
lene containing  substituents  in  the  a-positions,  by  chromic 
acid.  It  crystallizes  in  yellow  rhombic  plates,  melts  at  125°, 
and  is  the  complete  analogue  of  ordinary  quinone,  having  a 
similar  odour  and  being  volatile  with  steam.  It  can  be 
reduced  to  1 : 4-dihydroxy-naphthalene  by  sulphurous  acid, 
and  can  yield  a  dioxime,  hence  its  constitution  as  a  para- 
or  1 : 4-quinone.  (Formula  I.) 

/2-Naphthaquinone  (II)  has  no  odour  and  is  not  volatile, 
being  thus  more  like  phenanthraquinone.  It  can  be  obtained 
by  the  oxidation  of  l-amino-2-naphthol,  and  when  reduced 
with  sulphurous  acid  yields  1 :2-dihydroxy-naphthalene;  hence 
its  constitution  as  a  1 : 2  or  orthoquinone.  It  decomposes  at 
115°  without  melting  and  crystallizes  in  red  needles: 


2 : 6-Naphthaquinone  (III),  isomeric  with  the  a-  and  /?-com- 
pounds,  forms  odourless,  non- volatile,  yellowish -red  prisms, 
and  is  a  strong  oxidizing  agent. 

Hydroxy-naphthaquinones  are  known;  the  common  one  is 
2-hydroxy-a-naphthaquinone;  juglone  is  the  isomeric  5-hy- 
droxy-compound,  and  occurs  in  nut  shells;  naphthazarine, 
"alizarin  black",  is  a  valuable  dye  which  is  prepared  by  act- 
ing upon  a-dinitro-naphthalene  with  zinc  and  sulphuric  acid, 


504     XXXII.   ANTHRACENE  AND  PHENANTHRENE  GROUPS 

comports  itself  like  the  alizarin  dyes;  it  is  the  "alizarin"  of 
the  naphthalene  series. 

Carboxylic  Acids. — The  naphthoic  acids,  C10H7«C02H,  can 
be  obtained  by  saponifying  the  cyano-naphthalenes  and  also 
by  the  other  synthetical  methods  given  for  the  acids  of  the 
benzoic  series.  They  crystallize  in  fine  needles  sparingly  soluble 
in  hot  water,  and  break  up  into  naphthalene  and  carbon  di- 
oxide when  distilled  with  lime.  From  them  are  derived  the 
hydroxy-naphthoic  acids,  C10H6(OH)(C02H),  which  are  re- 
lated to  salicylic  acid  or  its  isomers.  Among  the  naphthalene- 
dicarboxylic  acids,  C10Hg(C02H)2,  which  are  known  may  be 
mentioned  naphthalic  acid,  (1:8),  which  at  a  somewhat  high 
temperature  yields  an  anhydride  similar  to  phthalic  anhydride. 

Phenyl-naphthalene,  C10H7(C6H5),  has  also  been  prepared; 
it  is  a  compound  built  up  of  a  naphthalene  and  of  a  benzene 
nucleus,  and  is  therefore  analogous  to  diphenyl,  G6H5»C6H5. 
The  same  applies  to: 

Di-naphthyl,  C10H7  •  C10H7,  which  yields  derivatives  (e.g.  the 
di-naphthols,  see  p.  502)  analogous  to  those  of  diphenyl.  The 
three  modifications  which  are  theoretically  possible,  namely, 
the  a-a-,  /?-/?-,  and  a-/?-compounds,  are  known. 

Another  derivative  of  naphthalene  is  acenaphthene,  C12H10, 

^2 

(1:8),  which  is  found  in  coal-tar.     It  crystal- 
)H2 

lizes  in  colourless  prisms,  melts  at  95°,  boils  at  277°,  and  yields 
naphthalic  acid  on  oxidation. 


XXXII.  THE  ANTHRACENE  AND  PHENAN- 
THRENE GROUPS 

A,  Anthracene 

Anthracene,  C14H10  (Dumas  and  Laurent,  1832;  Fritzsche, 
1857),  is  formed,  together  with  benzene  and  naphthalene,  by 
the  destructive  distillation  of  coal  and,  generally,  by  the 
pyrogenous  reactions  which  give  rise  to  these  products,  e.g. 
by  passing  CH4,  C2H6,  C2H2,  the  vapour  of  alcohol,  &c., 
through  red-hot  tubes. 

Although  coal-tar  contains  only  some  0'25-0'45  per  cent  of 
anthracene,  it  is  the  chief  source  from  which  this  hydrocarbon 


ANTHRACENE  505 

is  obtained.  The  fraction  of  coal-tar  distilling  above  270°  and 
known  as  anthracene  oil  yields,  on  further  distillation  and 
digesting  with  solvent  naphtha,  a  solid  mass  known  as  50- 
per-cent  anthracene,  which  is  then  distilled  with  one-third  of 
of  its  weight  of  potassium  carbonate.  This  serves  to  remove 
carbazole  (p.  473),  which  yields  a  non- volatile  potassium  de- 
rivative -6  yNK,  and  the  distillate  consists  of  anthracene 

C6H/ 

and  phenanthrene.  The  phenanthrene  is  removed  by  extrac- 
tion with  carbon  disulphide,  and  the  anthracene  crystallized 
from  benzene. 

The  following  are  some  of  the  more  important  methods  by 
means  of  which  the  hydrocarbon  has  been  synthesised,  and 
they  throw  considerable  light  upon  its  constitution: — 

1.  By  heating  0-tolyl  phenyl  ketone  with  zinc  dust  (B.  7, 17) : 


2.  Together  with  dibenzyl,  by  heating  benzyl  chloride  with 
water  at  200°  (B.  7,  276): 

4C6H5.CH2C1  =  C14H10  +  C14HI4  +  4HC1. 

3.  From  o-bromo-benzyl  bromide  and  sodium  in  ethereal 
solution  dihydro-  anthracene  is  at  first  formed,  and  this  is 
converted  by  oxidation  (which  is  partly  spontaneous  during 
the  above  reaction)  into  anthracene  (B.  12,  1965): 


4.  By  heating  benzene  with  symmetrical  tetrabromo-ethane 
and  aluminic  chloride  (Anschutz,  B.  16,  623)  : 


BrCHBr 

I 
BrCHBr 


I          +  C6H6  =  C6H4 
rCH 


5.  When  phthalic  anhydride  is  heated  with  benzene  and 
aluminic  chloride,  o-benzoyl-benzoic  acid  is  formed,  and  this 
when  heated  with  phosphoric  anhydride  yields  anthraquinone 


506      XXXlI.    ANTHRACENE  AND  FHENANTHRENE  GROtJPS 

(Behr  and  v.  Dorp,  B.  7,  578),  which  on  reduction  with  zinc 
dust  gives  anthracene: 


-geH,  =  CoH4<gg>CeH4+H20; 

/ITT 

C6H4<gg>C6H4  +  6H    =  C6H4<^       >C6H4-f  2H20. 


6.  When  a  mixture  of  wi-xylene  and  styrene  is  treated  with 
concentrated  sulphuric  acid,  there  is  formed  a-tolyl-fl-phenyl- 

propane,  CH3«C6H4«CH2«CH<^Q|r  5,  which  decomposes  almost 

quantitatively  into  methane,  hydrogen,  and  methyl-anthracene 
when  strongly  heated  (B.  23,  3272). 

Constitution.  —  From  mode  of  formation  5,  the  anthracene 
molecule  is  seen  to  contain  two  benzene  nuclei,  C6H4,  joined 
together  by  a  middle  group,  C2H2.  The  carbon  atoms  of  this 
middle  group  are  likewise  linked  together,  as  is  seen  from 
mode  of  formation  4,  and  take  up  the  0-position  with  regard 
to  each  other  on  one  or  other  of  the  benzene  nuclei  (on  one 
nucleus  according  to  methods  of  formation  1  and  5,  and  on 
the  other  according  to  method  3;  for  further  proofs  of  this, 
see  e.g.  v.  Pechmann,  B.  12,  2124).  The  constitution  of  an- 
thracene is  thus  the  following  (Graebe  and  Liebermann,  A. 
Suppl.  7,  313): 


CH     CH     CH 

3H 

or 


The  two  carbon  atoms  of  the  middle  group  thus  form  a  new 
hexagon-ring  with  the  carbon  atoms  of  the  benzene  nuclei  to 
which  they  are  linked,  so  that  anthracene  may  also  be  looked 
upon  as  being  built  up  by  the  conjunction  of  three  benzene 

/CH\ 
nuclei.     Besides  the  formula  C6H4<^  I     yO6H4,  the  "quinoid" 

QJT  CH 

formula  CHTT>CH   has  also  to  be  taken  into  consider- 


ation (Armstrong,  P.  1890,  101;  Kehrmann,  B.  1894,  21,  3348), 

Properties  and  Behaviour.  —  Anthracene  crystallizes  in  colour 

less  plates  which  show  a  magnificent  blue  fluorescence.     It  is 


ANTHRACENE  DERIVATIVES  507 

insoluble  in  water  and  dissolves  only  sparingly  in  alcohol  and 
ether,  but  readily  in  hot  benzene.  It  melts  at  213°,  boils  above 
351°,  and  with  picric  acid  yields  an  additive  compound  which 
crystallizes  in  beautiful  red  needles  melting  at  138°. 

Anthracene  is  transformed  by  sunlight  into  the  polymeric 
para-anthracene,  (C14H10)2.  When  reduced  with  hydriodic  acid 
and  phosphorus  it  takes  up,  in  the  first  instance,  two  atoms  of 
hydrogen,  with  the  formation  of  9:10-dihydro-anthracene, 


(see  p.  505,  mode  of  formation  3).  This  crystallizes  in  colour- 
less plates,  melts  at  107°,  and  is  readily  soluble  in  alcohol.  It 
sublimes  readily  and  distils  without  decomposition,  but  yields 
anthracene  at  a  red  heat  or  when  warmed  with  concentrated 
sulphuric  acid. 

Further  addition  of  hydrogen  yields  the  hydrides  C14Hlfl 
and,  finally,  C14H24. 

DERIVATIVES  OF  ANTHRACENE 

Theoretically  three  isomeric  mono-derivatives  are  possible  in 
each  case,  viz.,  the  a-,  /?-,  and  -/-compounds : 


since  in  the  graphical  formula  given  on  the  preceding  page, 
1  =  4  =  5  =  8  =  a,  2  =  3  =  6  =  7  =  ft  and  9  =  10  =  7. 
The  observed  facts  are  in  complete  accordance  with  this. 

The  position  of  the  substituting  group  can  usually  be  deter- 
mined either  by  an  examination  of  the  oxidation  products,  e.g. 
if  it  be  in  the  y-position  it  will  be  eliminated  and  anthra- 
quinone  formed;  or  it  is  arrived  at  from  the  synthesis  of  the 
compound,  e.g.  in  the  case  of  alizarin,  the  formation  of  which 
from  catechol  and  phthalic  acid  shows  that  its  two  hydroxyls 
are  contained  in  one  and  the  same  benzene  nucleus. 

The  number  of  di-substituted  derivatives  is  large,  for  example, 
when  both  substituents  are  alike,  15  isomerides  are  theoretically 
possible. 


508     XXXII.  ANTHRACENE  AND  PHENANTHRENE  GROUPS 

Numerous  derivatives  of  anthracene  are  known,  e.g.  halogen-, 
nitro-,  amino-,  and  sulphonic  acid  derivatives. 

Hydroxy-anthracenes.  —  The  a-  and  /^-compounds  are  termed 
a-  and  /3-anthrols;  they  are  obtained  by  fusing  the  correspond- 
ing sulphonic  acids  with  alkali,  and  in  their  properties  closely 
resemble  phenols  and  naphthols. 

y-Hydroxy-anthracene  or  anthranol  may  be  obtained  by- 
reducing  anthraquinone  with  zinc  and  acetic  acid,  or  syntheti- 
cally, by  the  action  of  concentrated  sulphuric  acid  on  o- 
benzyl-benzoic  acid  at  80°  : 


It  is  readily  oxidized  to  anthraquinone,  and  with  hydroxyl- 
amine  yields  anthraquinone  oxime. 

Anthraquinone,  C14H8O2  (Laurent,  1834),  is  readily  obtained 
by  oxidizing  anthracene  with  chromic  acid  mixture  (which  is 
the  method  followed  on  the  large  scale),  or  with  chromic  an- 
hydride and  glacial  acetic  acid,  and  is  also  produced  when 
calcium  benzoate  is  distilled. 

It  crystallizes  in  yellow  prisms  or  needles  soluble  in  hot 
benzene,  melts  at  285°,  sublimes  with  great  readiness,  and  is 
exceedingly  stable  as  regards  oxidizing  agents.  Hydriodic 
acid  at  150°  reduces  it  either  to  anthracene  or  its  dihydride, 
while  fusion  with  potash  converts  it  into  benzoic  acid.  It 
possesses  more  of  a  ketonic  than  of  a  quinonic  character 
(Zincke,  Fittig),  as  it  is  not  reduced  by  sulphurous  acid,  and 
gives  an  oxime  with  hydroxylamine. 

It  yields  mono-  and  dibromo-,  nitro-  and  sulphonic  -  acid 
derivatives.  Anthraquinone  /3-mono-sulphonic  acid  crystal- 
lizes in  yellow  plates,  and  is  formed  by  the  action  of  sul- 
phuric acid  under  normal  conditions,  but  in  the  presence  of 
mercury  salts  the  isomeric  a  -acid  is  obtained;  of  the  di- 
sulphonic  acids  two  are  formed  directly  from  anthraquinone, 
and  two  may  be  prepared  by  the  oxidation  of  the  correspond- 
ing anthracene-disulphonic  acids. 

Fusion  of  the  sulphonic  acids  with  potash  does  not  generally 
yield  the  analogous  hydroxy-compounds  in  theoretical  quantity, 
oxygen  being  usually  absorbed  from  the  air  at  the  same  time  ; 
thus  the  mono-sulphonic  acids  yield  mono-  and  dihydroxy-, 
and  the  di-sulphonic  acids  di-  and  trihydroxy-anthraquinones. 
In  practical  working  the  theoretical  amount  of  chlorate  of 


ALIZARIN  509 

potash  required  is  added  to  the  "melt".     Prolonged  fusion 
with  potash  tends  to  form  hydroxy-benzoic  acids. 

Various  hydrpxy-anthraquinones  can  also  be  prepared  by 
the  synthetical  mode  of  formation  5,  p.  505,  viz.,  from  phthalic 
anhydride  and  the  mono-  or  dihydroxy-benzenes  (Baeyer  and 
Caro,  B.  7,  792;  8,  152),  e.g.: 


phenol  yields  by  this  method  the  two  hydroxy-anthraquinones 
(yellow  needles),  catechol  yields  alizarin,  quinol  yields  quini- 
zarin,  and  so  on.  The  hydroxy-derivatives  are  further  pro- 
duced by  fusing  chloro-  and  bromo-anthraquinones  with  potash, 
while  m-  hydroxy-benzoic  acid  can  be  converted  directly  by 
sulphuric  acid  into  anthraflavic  acid,  water  being  eliminated. 
Cf.  A.  240,  245. 

Alizarin,  1  :  2-dihydroxy-anthraquinone,  CUH804,  is  the  most 
important  constituent  of  the  beautiful  red  dye  of  the  madder 
root  (Eubia  tinctorum),  which  has  been  known  for  ages,  being 
present  in  the  latter  as  the  readily  decomposable  glucoside, 
Euberythric  acid,  C^HggO^;  in  addition  to  alizarin,  madder 
also  contains  purpurin.  It  is  manufactured  on  the  large  scale 
by  fusing  anthraquinone-/3-sulphonic  acid  with  potassic  hy- 
droxide and  chlorate  (Graebe  and  Liebermann,  Caro,  Perkin,  B. 
3,  359;  A.  160,  130). 

It  crystallizes  in  magnificent  red  prisms  or  needles  of  a  glassy 
lustre,  melts  at  289°,  and  can  be  sublimed;  it  dissolves  readily 
in  alcohol  and  ether,  only  sparingly  in  hot  water,  but,  as  a 
phenol,  very  readily  in  alkalis  to  a  violet-red  solution.  It 
yields  insoluble  coloured  compounds  —  the  so-called  "lakes" 
—  with  metallic  oxides,  the  alumina  and  tin  lakes  being  of  a 
magnificent  red  colour,  iron  lake  violet-black,  and  lime  lake 
blue.  In  the  Turkey  Red  manufacture,  for  instance,  the 
materials  to  be  dyed  are  previously  mordanted  with  acetate 
of  alumina  or  with  "  ricinoleic-sulphuric  acid". 

Its  constitutional  formula  is  based  on  the  following  con- 
siderations: —  (a)  Its  conversion  into  anthracene  when  heated 
with  zinc  dust  (Graebe  and  Liebermann,  B.  1868,  1,  49;  A.  Sup. 
7,  297);  (b)  its  formation  by  fusing  dibromo-anthraquinone  or 
anthraquinone-sulphonic  acid  with  potash;  (c)  its  synthesis  from 
phthalic  anhydride  and  catechol. 

All   these  indicate  that  it  is  a  dihydroxy-anthraquinone 


510     XXXII.   ANTHRACENE  AND  PHENANTHRENE  GROUPS 

with  the  two  hydroxy-groups  in  the  0-positions  with  respect 
to  one  another: 

CO      OH 

S\       yVAA,.         /\ 

H  /Y      Vl011 

2:3     or  1:2. 

w/J 

The  fact  that  two  isomeric  mono-nitro-derivatives  (with  the 
nitro-group  in  the  same  nucleus  as  the  two  hydroxy-groups) 
have  been  prepared  is  a  proof  of  the  positions  1:2  for  the 
hydroxy-groups. 

C(OH) 

Anthrarobin,  dihydroxy-anthranol,  C6H4<(  ^>C6H2(OH)2, 

XCH — / 

obtained  from  alizarin,  ammonia,  and  zinc  dust,  is  a  yellowish- 
white  powder  which  yields  alizarin  on  oxidation;  on  account 
of  its  reducing  properties  it  is  used  in  skin  diseases. 

Nitric  peroxide  converts  alizarin  into  /2-nitro-alizarin  or  ali- 
zarin orange,  C14H7(N02)04,  a  yellowish-red  dye;  and  this  with 
glycerol  and  sulphuric  acid  (the  Skraup  reaction,  p.  542),  yields 
alizarin  blue,  C17H9N04  (see  Quinoline),  a  valuable  blue  dye 
which  is  converted  by  fuming  sulphuric  acid  into  alizarin  green. 

Purpurin,  l:2-A-trihydroxy-,  anthrapurpurin,  1:2:7 -trihydroxy-, 
and  flavopurpurin,  l:2:Q-trihydroxy-anthraquinone,  are  also  valu- 
able dyes  which  are  manufactured  on  a  large  scale;  the  same 
applies  to  the  isomeric  compound  anthragallol,  l:2:3-trihydroxy- 
anthraquinone,  or  "anthracene  brown",  which  is  prepared  by 
acting  on  a  mixture  of  gallic  and  benzoic  acids  with  concen- 
trated sulphuric  acid. 

Tetra-,  penta-,  and  hexa-hydroxyanthraquinones  are  also  used 
as  dyes.  (B.  1890,  23,  3739;  J.  pr.  43,  237,  246.)  Alizarin 
bordeaux  is  a  l:2:5:8-tetrahydroxy-  and  alizarin- cyanine 
1:2:4:5: 8-pentahydroxy  anthraquinone. 

According  to  v.  Kostanecki  the  colouring  power  of  these  com- 
pounds is  connected  with  the  presence  of  two  hydroxyls  in  the 
ortho-position  to  one  another. 

For  Indanthrene  dyes  see  B.  36,  3410. 

B.  Phenanthrene 

Phenanthrene  (Fittig  and  Ostermeyer,  1872,  A.  166,  361) 
which  is  isomeric  with  anthracene,  accompanies  this  hydro- 
carbon in  coal-tar.  It  crystallizes  in  colourless  glistening 


PHENANTHRENE  511 

plates,  dissolves  in  alcohol  more  readily  than  anthracene 
(yielding  a  blue  fluorescent  solution),  melts  at  99°,  and  boils 
at  340°.  It  may  be  separated  from  anthracene  by  partial 
oxidation  and  subsequent  distillation,  as  the  latter  is  more 
readily  attacked.  Oxidizing  agents  convert  it  into  diphenic 
acid  (p.  474).  Its  picrate  crystallizes  in  yellow  needles  melt- 
ing at  145°. 

It  may  also  be  obtained: — 1.  By  leading  the  vapour  of  tolu- 
ene, stilbene,  dibenzyl  or  0-ditolyl  through  a  red-hot  tube,  thus : 

•  CH,        OEL-CH 


2.  Together  with  anthracene  from  0-bromo-benzyl  bromide 
and  sodium. 

3.  A  recent  synthesis  by  Pschorr  (B.  1896,  29,  496;  32,  162, 
176;  33,  496)  is  from  0-nitro-benzaldehyde.     This  with  sodic 
phenyl-acetate  and  acetic  anhydride  (Perkiris  synthesis,  p.  441) 
yields  a-phenyl-o-nitro-cinnamic  acid,  N02  •  C6H4  •  CH :  CPh  • 
C02H.     When  this  is  reduced,  diazotized,  and  treated  with 
copper  powder,   /3-phenanthrene-carboxylic  acid  is  formed, 
C6H4.CH 

,  and  when  carbon  dioxide  is  eliminated  this 
(C6H4«C«C02H 

yields  phenanthrene.  Numerous  phenanthrene  derivatives 
have  been  synthesised  in  a  similar  manner.  (See  also  Robe, 
B.  1898,  31,  1896.) 

The  formation  of  phenanthrene  from  0-ditolyl,  and  its  oxi- 

C6H4.C02H 
dation  to  diphenic  acid,   •  ,  show  that  it  is  a  diphenyl 


derivative,  and  that  it  contains  a  carbon  atom  linked  to  each 
benzene  nucleus;  this  carbon  atom  is  joined  to  the  corre- 
sponding one  by  a  double  bond,  as  is  shown,  e.g.,  by  its 

C6H5.CH 
formation   from  stilbene,  •  •   ,   a   reaction   completely 

analogous  to  the  preparation  of  diphenyl  from  benzene.  Since 
diphenic  acid  is  a  di-ortho-diphenyl-dicarboxylic  acid  (Schultz, 
A.  196,  1 ;  203,  95),  phenanthrene  is  also  a  di-ortho-derivative 
and  possesses  the  following  constitution: 

CH    CH 
^  C     CH 

CVH4.CH     °r 


512      XXXII.    ANTHRACENE  AND  PHENANTHRENE  GROUPS 

According  to  the  above  formula,  the  two  CH-groups  form  a 
new  hexagon  ring  with  the  carbon  atoms  of  the  two  benzene 
nuclei  to  which  they  are  linked,  so  that  phenanthrene  —  like 
anthracene  —  may  be  looked  upon  as  the  product  of  the  coali- 
tion of  three  benzene  nuclei,  or  of  one  naphthalene  and  one 
benzene  nucleus. 

Additive  and  substitution  products  of  phenantbrene  are  also 
known,  e.g.  a  tetrahydride,  nitro-,  amino-,  cyano-,  and  hydroxy- 
compounds,  and  sulphonic  and  carboxylic  acids.  Phenanthrol, 
C14H9(OH),  is  a  hydroxy-  phenanthrene,  and  phenanthrene- 
quinol,  C14H8(OH)2,  a  dihydroxy-compound;  when  oxidized 

C6H4-CO 
the  latter  yields  phenanthraquinone,    •         •    ,  which  may 

C6H4  •  CO 

also  be  prepared  directly  from  phenanthrene  and  chromic  acid. 
It  crystallizes  in  odourless,  orange  needles,  melts  at  200°, 
distils  unchanged,  and  is  not  volatile  in  steam.  Phenanthra- 
quinone possesses  the  character  of  a  diketone,  reacting  with 
hydroxylamine,  sodium  bisulphite,  &c.,  but  it  can  be  reduced 
to  the  corresponding  quinol  by  sulphurous  acid.  It  gives  a 
bluish-green  coloration  with  toluene  containing  thio-tolene, 
glacial  acetic  acid,  and  sulphuric  acid,  and  when  the  mixture 
is  diluted  and  extracted  with  ether  the  latter  becomes  violet- 
coloured;  this  is  the  Laubenheimer  reaction  (B.  17,  1338). 

i  C.  Complex  Hydrocarbons 

Fluoranthene,  C15H10,  pyrene,  C16H10,  chrysene,  C18H12, 
retene,  C18H18,  and  picene,  C22H14,  are  hydrocarbons  which 
have  been  isolated  from  that  portion  of  coal-tar  which  boils 
above  360°.  Phenanthrene,  pyrene,  and  fluoranthene  are  also 
found  in  "Stupp"  fat,  i.e.  the  fat  obtained  as  a  by-product 
from  the  working  up  of  mercury  ores  in  Idria.  They  all  crys- 
tallize in  white  plates,  sublime  without  decomposition,  and 
when  oxidized  are  converted  into  the  corresponding  ketones. 
Their  constitution  is  expressed  by  the  following  formulae: 


C6H4.CH  C6H4.CH  C10H6.CH 

•          ••         r^TT  v.    •         ••  •          •• 

C6H3£gCH      C10H6.CH     ^>C6H2.CH  C10H6.CH 

Fluoranthene  Chrysene  Retene  or  Methyl  Picene. 

iso-propyl  phenanthrene 

(Cf.  A.  240,  147;  284,  52;  351,  218;  B.  26,  1745;  B.  36, 
4200.) 


HETEROCYCLIC  COMPOUNDS  513 

HETEEOCYCLIC   COMPOUNDS 

XXXIII.  INTRODUCTION 

The  third  great  division  of  carbon  derivatives  consists  of 
the  Heterocydic  Compounds.  These,  like  the  carbocyclic  com- 
pounds, contain  a  closed  chain  or  ring,  but  differ  from  the 
latter  by  the  presence  in  the  actual  ring  of  atoms  of  elements 
other  than  carbon  (cf.  formulae,  p.  514).  The  number  of  such 
compounds  is  enormous,  although  the  number  of  elements 
usually  associated  with  carbon  in  rings  is  comparatively  small. 
The  more  common  elements  are  oxygen  and  sulphur,  but  more 
especially  nitrogen. 

A  number  of  these  compounds  have  been  already  mentioned; 
among  the  oxygen  compounds  are  ethylene  oxide,  glycolide, 
phthalic  anhydride,  and  among  the  nitrogen  compounds  suc- 
cinimide,  phthalimide,  and  lactams. 

The  compounds  are  divided  into  groups  according  to  the 
number  of  atoms  constituting  the  ring,  thus  three-membered 
rings,  e.g.  ethylene  oxide;  four-membered  rings,  e.g.  betaine; 
five-membered  rings,  e.g.  thiophene;  six-membered  rings,  e.g. 
pyridine,  &c.  As  in  the  carbocyclic  series,  the  most  important 
and  also  the  most  stable  are  the  five-  and  six-membered  rings. 
A  further  division  of  these  groups  can  be  made  according  to 
the  number  of  atoms  other  than  carbon  present.  Thus  in  the 
five-membered  ring  compounds  we  can  have  the  following  sub- 
groups: 40  +  IN;  30  +  2N;  20  +  3N;  termed  respectively 
the  monazole,  di-  and  tri-azole  sub-groups. 

The  stability  of  the  compounds  and  their  general  chemical 
characteristics  depend  to  a  large  extent  on  the  saturated  or 
unsaturated  nature  of  the  rings.  Compounds  like  thiophene, 
pyrrole  and  pyridine  are  stable  and  closely  resemble  ben- 
zene— they  possess  general  aromatic  properties.  Like  benzene 
they  can  be  reduced,  the  two  former  can  each  take  up  two  or 
four  atoms  of  hydrogen,  and  pyridine  two,  four  or  six.  These 
reduction  products  no  longer  have  aromatic  properties.  It  is 
interesting  to  note  that  although  the  five-membered  hetero- 
cyclic  unsaturated  compounds  resemble  benzene,  the  unsatu- 
rated carbocyclic  compound  cyclopentadiene  does  not. 

Some  of  the  common  heterocyclic  compounds  contain  con- 
densed nuclei,  i.e.  the  two  condensed  rings  have  two  carbon 
atoms  in  common.  A  well-known  example  of  condensed 

(9480)  2K 


514  XXXIII.   HETEROCYCLIC  COMPOUNDS 

heterocyclic  rings  is  met  with  in  purine  and  its  derivatives 
(p.  290).  Examples  of  compounds  containing  a  benzene 
nucleus  condensed  with  a  heterocyclic  ring  are  met  with  in 
quinoline,  coumarone  and  indole  (see  below). 

Compounds  with  condensed  nuclei  behave  very  differently 
on  oxidation.  Certain  of  them  have  the  heterocyclic  ring 
ruptured,  and  thus  yield  ortho-derivatives  of  the  carbon  ring; 
others,  again,  have  the  carbon  ring  ruptured,  and  yield  ortho- 
acids  of  the  heterocyclic  ring.  The  compounds  dealt  with  in 
the  following  sections  will  be  grouped  as  follows: 

1.  Five-membered  heterocyclic  compounds  containing  4C 
-f  10,  S  or  N  atoms,  or  the  furane  group,  e.g.: 


CH:CH\  CH:CH 

CH:CH/^         CHi 

Furane  Thiophene  Pyrrole 


:CH\  CEL:GR\ 

iCH/  CH:CHX 


2.  Compounds  formed  by  the  condensation  of  these  rings 
with  a  benzene  nucleus,  e.g.: 


Coumarone,  Indole,  j 


3.  Five-membered  heterocyclic  compounds  containing  three 
carbon  atoms,  e.g.  pyrazole  and  thiazole  group. 

4.  Six-membered  heterocyclic  compounds  or  pyridine  group, 
e.g.: 

CH    CH 

Pyridine,  HC/         \N 


5.  The  compounds  formed  by  the  condensation  of  a  benzene 
and  pyridine  ring,  e.g.  : 


Quinoline,  I       I       j      and      wo-Quinoline, 


6.  Six-membered  heterocyclic  compounds,  with  not  more 
than  four  carbon  atoms  in  the  ring. 


ffURANE  GROUP  515 

XXXIV.   FURANE  GROUP 
CH:CH/C          CH:CH/S         CH:< 

Furane  Thiophene  Pyrrole. 

From  these  compounds  a  whole  series  of  derivatives  are 
obtained  by  the  substitution  of  hydrogen  by  halogen,  and 
also  by  the  entrance  of  the  groups  'CH3,  •CHgOH,  «CHO, 
•  C02H,  &c.  In  their  properties  furane,  thiophene,  and  pyrrole 
remind  one  of  benzene.  Thiophene,  in  particular,  is  delusively 
like  the  latter,  e.g.  in  odour  and  boiling-point,  and  its  various  de- 
rivatives often  show  a  marvellous  similarity  in  their  chemical  and 
physical  relations  to  the  corresponding  derivatives  of  benzene. 

Furane,  pyrrole,  and  thiophene  also  resemble  one  another  in 
many  respects.  All  three  boil  at  relatively  low  temperatures 
(  -f-  32°,  131°,  84°),  are  either  insoluble  or  only  sparingly  soluble 
in  water,  but  readily  in  alcohol  and  ether,  and  show  many  an- 
alogous colour  reactions.  Thus  pyrrole  and  thiophene  and  their 
derivatives  give,  for  the  most  part,  an  intense  violet  to  blue 
coloration  when  mixed  with  isatin  and  concentrated  sulphuric 
acid,  and  a  cherry-red  or  violet  coloration  with  phenanthra- 
quinone  and  glacial  acetic  or  sulphuric  acid.  The  vapour  of 
pyrrole  colours  a  pine  shaving  which  has  been  moistened  with 
hydrochloric  acid  carmine  red  (irvppos,  fiery-red),  while  furalde- 
hyde  vapour  colours  it  an  emerald  green;  the  latter  likewise 
colours  a  piece  of  paper  moistened  with  xylidine-  or  aniline- 
acetate  red.  Furane  is  converted  by  mineral  acids,  e.g.  hydro- 
chloric acid,  into  an  insoluble  amorphous  powder,  and  pyrrole 
into  an  insoluble  amorphous  brown-red  powder,  "  pyrrole-red  " 
(with  evolution  of  ammonia),  while  thiophene  remains  unal- 
tered; the  derivatives  show  a  similar  behaviour.  Pyrrole  is 
distinguished  from  the  two  other  compounds  by  having  feebly 
basic  properties. 

Derivatives  of  all  three  compounds  may  be  obtained  from 
mucic  acid,  C02H  •  (CH  •  OH)4  •  C02H  (p.  259).  When  distilled, 
mucic  acid  yields  pyromucic  acid  or  furane-a-carboxylic  acid; 
when  its  ammonium  salt  is  distilled,  pyrrole  is  formed;  and 
when  free  mucic  acid  is  heated  with  barium  sulphide,  thiophene 
a-carboxylic  acid  is  obtained,  e.g. : 

CH.:(OH):.CiHi  ;;(OH)I.:COO:H  CH:CH . 

=  C02+3H20+ 1  >0. 

3iIi;(0:.H).i     COOH  CH:C(C02H)/ 


516  XXXIV.   FURANE  GROUP 

A  very  general  method  for  the  formation  of  derivatives  of 
this  group  is  from  y-diketones,  e.g.  acetonyl-acetone,  CH3«CO« 
CH2.CH2.CO.CH3  (p.  221;  also  p.  230).  When  this  com- 
pound is  heated  with  phosphorus  pentoxide  or  zinc  chloride, 
dimethyl  -furane  is  formed;  with  phosphorus  pentasulphide, 
dimethyl-thiophene;  with  alcoholic  ammonia,  dimethyl-pyrrole 
(B.  18,  58,  367;  20,  1074). 

This  behaviour  would  indicate  that  the  acetonyl-  acetone 
reacts  as  the  tautomeric  compound: 

m,C(OH):CH.CH:C(OH).CHa    or 


upon  this  assumption  the  formation  of  dimethyl-furane  appears 
simply  as  that  of  an  anhydride,  that  of  dimethyl-pyrrole  as  an 
exchange  of  2  (OH)  for  NH  (imide  formation),  and  that  of  di- 
methyl-thiophene as  the  formation  of  a  sulphide,  i.e.  exchange 
of  2(OH)  for  S,  according  to  the  following  equations  : 

H        CH:C(CH3K 
H  "  CH:C(CH3)/ 
CH:C(CH3>OH        CH:C(CH3)\ 

T  " 


H        CH:C(CH 
r  H        CH:C(CH 


From  the  above  reactions  the  constitutional  formula  for  the 
three  compounds  would  be: 


Furane  Thiophene                             Pyrrole 

CH:CHv  CH:CHv  ^ 

CH:CBX  CH:CH/  CH: 

(ft)      W  03)       (a)  03)       (a) 


These  formulae  receive  corroboration  from  the  frequently  ob- 
served fact  that  the  substances  are  capable  of  yielding  additive 
compounds  with  bromine  or  hydrogen  (see  Pyrroline).  Ac- 
cording to  the  above  formulae,  two  isomeric  mono-substituted 
derivatives  of  furane  and  thiophene  are  possible:  (1)  one  in 
which  the  hydrogen  atom  (a)  which  stands  nearest  to  the 
oxygen,  sulphur,  or  nitrogen  atom,  and  (2)  one  in  which  a 
quasi-middle  hydrogen  atom  (ft)  is  substituted.  AM  a  matter 


FtTRANE.      FUROL  517 

of  fact,  two  such  isomers  have  been  observed  in  many  cases, 
e.g.  two  thiophenic  acids.  These  form  mixed  crystals,  the 
crystals  having  a  homogeneous  appearance  although  they  con- 
tain both  acids  (V.  Meyer,  A.  236,  200).  In  the  case  of  pyrrole, 
on  the  other  hand,  three  kinds  of  derivatives  (a-,  /?-,  and  n-) 
are  both  possible  and  known. 

An  examination  of  the  molecular  refraction  of  thiophene 
and  also  of  its  heat  of  combustion  (B.  1885,  18,  1832)  point  to 
the  presence  of  only  one  double  bond  in  the  thiophene  mole- 

PTT « PTT\ 
cule.     The  formula   ••       •     J>S  has  been  suggested,  and  this 

CH  •  CH/ 

is  quite  in  harmony  with  the  production  of  substituted  maleic 
acids  by  the  oxidation  of  thiophene  derivatives.  Probably  the 
simplest  explanation  is  that  the  thiophene  molecule  contains 
centric  bonds,  and  should  be  represented  as: 


Furane  or  furfurane  is  a  colourless  mobile  liquid,  boiling  at 
32°,  and  with  an  odour  resembling  that  of  chloroform.  It  is 
present  in  pine-wood  tar,  in  the  first  runnings  from  ordinary 
wood  tar,  &c.,  and  is  obtained  by  the  distillation  of  sugar  with 
lime,  or  by  distilling  barium  pyromucate.  a-Methyl-furane  or 
sylvane  is  likewise  present  in  pine-wood  tar,  and  in  the  pro- 
ducts of  distillation  of  sugar  with  lime.  It  boils  at  65°.  aa- 
Dimethyl-furane  is  obtained  from  sugar  and  lime,  and  also 
from  acetonyl-acetone  (p.  516).  It  is  a  colourless  mobile  liquid 
of  a  characteristic  odour,  and  boils  at  94°.  Concentrated  acids 
convert  it  into  a  resin;  it  can  be  transformed  back  into 
acetonyl-acetone. 

Furol,  a-furaldehyde  or  furfuraldehyde,  C4H30«CHO  (Dobe- 
reiner),  is  obtained  when  pentoses,  e.g.  arabinose  and  xylose, 
are  distilled  with  concentrated  hydrochloric  acid: 

C6H1006  -  3H20  =  C6H402. 

The  yield  is  quantitative,  and  the  method  is  made  use  of  foi 
determining  the  amounts  of  pentoses  present  in  various  sub- 
stances. 

It  may  also  be  obtained  by  distilling  bran,  wood,  sugar,  or 
various  carbohydrates  with  moderately  concentrated  sulphuric 


618  XXXIV.  FURANE  GROUP 

acid.  It  is  a  colourless  oil  of  agreeable  odour,  turns  brown 
in  the  air,  and  boils  at  162°. 

It  possesses  all  the  properties  of  an  aldehyde,  and  can  yield 
condensation  products  in  much  the  same  manner  as  benzalde- 
hyde  (p.  424):  e.g.  furom,  C4H3O.CH(OH).(X).C4H20,  corre- 
sponding with  benzoin;  furalmalonic  acid,  C4H30-CH:C 
(C02H)2,  corresponding  with  benzalmalonic  acid;  and  furyl- 
acrylic  and  aZfo-furylacrylic  acid,  C4H30  •  CH  :  CH  •  C02H, 
corresponding  with  cinnamic  and  a/fo-cinnamic  acids. 

Pyromucie  acid,  C4H30-C02H. — Furane-a-carboxylic  acid 
crystallizes  in  needles  or  plates  similar  to  those  of  benzoic 
acid,  and  melts  at  132°;  it  sublimes  easily,  is  readily  soluble 
in  hot  water  and  alcohol,  and  decolorizes  alkaline  permangan- 
ate almost  instantaneously. 

Pyrrole  is  a  constituent  of  coal-tar  (Runge)  and  of  bone-oi1 
(Anderson);  it  boils  at  131°,  and  possesses,  like  many  of  its 
homologues,  a  chloroform  odour.  It  is  a  secondary  base,  and 
its  imino-hydrogen  is  replaceable  by  metals  and  alkyl,  or  acyl 
radicals. 

In  addition  to  the  methods  of  formation  mentioned  on  p.  516, 
it  may  also  be  obtained  vby  heating  succinimide  (p.  239)  with 
zinc  dust,  or  from  acetylene  and  ammonia  at  a  red  heat. 

When  pyrrole  is  acted  upon  by  hydroxylamine  the  ring  is 

CH2.CH:N.OH 

broken,  and  the  dioxime  of  succmic-aldehyde,  •  , 

CH2  •  CH :  N  •  OH 

is  formed;  this  yields  tetramethylene-diamine  upon  reduction 
(R  22,  1968).  Dimethyl-pyrrole  in  a  similar  manner  yields 
acetonyl-acetone-dioxime. 

w-Potassium-pyrrole,  C4H4NK,  which  is  obtained  from  pyr- 
role and  potassium  or  solid  potassic  hydroxide,  is  a  colourless 
compound  which  is  decomposed  by  water.  A  number  of 
w-alkyl  and  acyl  derivatives  may  be  prepared  by  the  aid  of 
this  potassium  compound,  but  most  of  them  are  relatively 
unstable,  and  when  heated  are  transformed  into  the  isomeric 
a-alkyl  or  acyl  compounds.  A  most  interesting  reaction  is  the 
conversion  of  pyrrole  into  pyridine  (p.  533)  by  means  of  sodium 
methoxide  and  chloroform  or  methylene  iodide.  By  the  action 
of  iodine  and  alkali,  substitution  takes  place  with  the  forma- 
tion of  tetra-iodo-pyrrole  or  iodole,  C4I4(NH),  which  crystal- 
lizes in  yellow  plates,  and  is  used  as  an  antiseptic  in  place  of 
iodoform. 

Zinc  and  glacial  acetic  acid  convert  pyrrole  into  pyrroline, 


tHIOPHENE  619 


34,  3954),  a  colourless  liquid  boiling  at  91°  and  also  a  strong 
secondary  base;  when  this  latter  is  heated  with  hydriodic 

r^TT     OTT 

acid,  it  is  further  reduced  to  pyrrolidine,    •    2          yNH,  a 

CH2  •  CH2/ 

colourless,  strongly  alkaline  base  resembling  piperidine,  and 
boiling  at  86°.  It  is  also  formed  by  the  action  of  sodium  on 
an  alcoholic  solution  of  succinimide,  and  is  obtained  synthetic- 
ally by  heating  S-chloro-butylamine  with  alkali,  and  by  treating 
ethylene  cyanide  with  sodium  and  alcohol,  thus  : 


CH2.CN  CH2.CH2.NH2        C 

CH2.CN  4  CH2.CH2.NH2'  =  CH2.CH/N 

it  is  consequently  designated  tetramethylene-imine  (Ladenburg, 
B.  19,  782;  20,  442). 

The  red  colouring  matter  of  blood  yields  pyrrole  derivatives 
as  some  of  its  products  of  decomposition,  and  pyrrolidine 
derivatives,  especially  pyrrolidine  -carboxy  lie  acid  (proline), 
are  decomposition  products  of  albumen. 

Thiophene  (V.  Meyer,  B.  16,  1465,  &c.)  is  present  in  coal- 
tar,  being  invariably  found  in  benzene  (up  to  0*5  per  cent); 
the  same  applies  to  its  homologues  thiotolene  (methyl-thio- 
phene),  and  thioxene  (dimethyl-thiophene),  which  accompany 
toluene  and  xylene,  &c.  Its  boiling-point  (84°)  is  almost  the 
same  as  that  of  benzene  (80-4°),  from  which  it  is  extracted  by 
repeatedly  shaking  with  small  quantities  of  concentrated  sul- 
phuric acid,  which  transforms  the  thiophene  into  a  soluble 
sulphonic  acid  (B.  17,  2641,  2852).  It  is  also  attacked  more 
readily  than  benzene  by  other  reagents,  such  as  halogens. 

Thiophene  is  also  obtained  synthetically  by  leading  the 
vapour  of  ethyl  sulphide  through  a  red-hot  tube  (Kekutt),  and 
in  small  quantity  by  heating  crotonic  acid,  w-butyric  acid, 
paraldehyde,  &c.,  with  phosphorus  pentasulphide. 

Stilbene  (p.  478)  and  sulphur  yield  tetraphenyltMophene, 
thionessal,  m.-pt.  183°. 

The  preparation  and  properties  of  the  thiophene  derivatives 
are  almost  identical  with  those  of  the  corresponding  benzene 
compounds.  Thus  nitric  acid  acts  on  thiophene  to  produce 
a  nitro-thiophene,  analogous  to  nitro-benzene,  which  can  in 
its  turn  be  reduced  to  amino-thiophene;  the  latter  is,  how- 
ever, much  less  stable  than  the  corresponding  ammo-benzene. 


620      XXXV.    CONDENSED  BENZENE,   FURANE,    ETC.   RINGS 

The  boiling-points  of  thiophene  compounds  and  their  corre- 
sponding benzene  derivatives  are  almost  identical. 

The  homologues  can  be  obtained  by  Fittig's  synthesis,  the 
a-compounds  from  1 : 4-diketones,  and  the  /^-derivatives  from 
mono-  or  di-substituted  succinic  acids  and  phosphorus  penta- 
sulphide. 

Thiophene-sulphonic  acid,  OH«S02»C4H3S,  decomposes  into 
thiophene  and  sulphuric  acid  when  superheated  with  water, 
and  does  not  yield  a  phenol  on  fusion  with  potash. 

Hydroxythiotolene,  C4H2S(CH3)(OH),  the  phenol  of  thiotol- 
ene,  is  formed  by  heating  Isevulic  acid  with  P2S5  (B.  19,  553). 

A  mixture  of  the  a-  and  /3-monocarboxylic  acids  when 
crystallized  slowly  from  water  yields  mixed  crystals,  which 
cannot  be  resolved  into  their  components. 

The  blue  coloration  which  is  formed  when  benzene  contain- 
ing thiophene  is  shaken  with  isatin  and  concentrated  sulphuric 
acid,  is  due  to  the  formation  of  the  blue  colouring  matter 
"Indophenin",  C^ONS. 

(Of.  V.  Meyer's  "Die  Thiophengruppe",  Braunschweig,  1888.) 


XXXV.  COMPOUNDS  FORMED  BY  THE  CONDEN- 
SATION OF  A  BENZENE  NUCLEUS  WITH  A 
FURANE,  THIOPHENE,  OR  PYRROLE  RING 


NH 

Coumarone  Benzo-thiophene  Indole. 

Coumarone  closely  resembles  pseudo-cumene.  It  occurs  in 
coal-tar,  and  may  be  isolated  as  its  picrate.  It  is  usually 
obtained  from  bromocoumarin;  this  with  alcoholic  potash 
yields  coumarilic  acid  which  gives  coumarone  when  distilled 
with  lime: 


It  is  a  colourless  liquid  distilling  at  170°;  yields  a  dibromide 
and  a  dihydro-derivative,  thus  indicating  the  presence  of  a 
double  bond.  Numerous  derivatives  are  known. 


INDOLE  621 

Benzo-tkiopkene,  Thionaphthene,  melts  at  31°,  boils  at  221°, 
and  has  an  odour  resembling  naphthalene. 

INDOLE  GROUP 

Indole  (Baeyer,  1868)  is  the  most  important  compound  in 
this  group,  as  it  is  the  parent  substance  of  indigo.  As  a 
derivative  of  pyrrole  it  possesses  feebly  basic  properties.  It 
is  obtained  by  distilling  oxindole  with  zinc  dust;  by  heating 
o-nitro-cinnamic  acid  with  potash  and  iron  filings;  by  the 
action  of  sodic  ethoxide  upon  o-amino-/?-chloro-styrene  (B.  17, 
1067): 

C6H4<^:aCHC1  +  NaO.C2H5  =  OJEL^^^CH.  +  NaCl  +  C2HSOH; 

by  the  pancreatic  fermentation  of  albumen;  together  with 
skatole  by  fusing  albumen  with  potash;  and  by  passing  the 
vapours  of  various  anilines,  e.g.  diethyl-o-toluidine,  through 
red-hot  tubes,  &c.  It  occurs  in  the  essential  oil  of  jasmine 
flowers,  crystallizes  in  plates,  melts  at  52°,  volatilizes  readily 
with  steam,  and  usually  has  a  peculiar  faecal -like  odour, 
although  in  the  pure  state  and  diluted  it  is  stated  to  have  a 
fragrant  odour.  It  is  feebly  basic,  colours  a  pine  shaving 
which  has  been  moistened  with  hydrochloric  acid  cherry-red, 
with  nitrous  acid  gives  a  red  precipitate,  which  consists  partly 
of  the  so-called  nitroso-indole,  [C8H6N(NO)]2  (a  delicate  re- 
action; see  B.  22,  1976),  and  yields  acetyl-indole  when  acety- 
lated.  These  last  reactions  show  that  indole  contains  an  imino- 
group.  When  oxidized  with  ozone  it  yields  indigo. 

The  system  of  numbering  the  substituents  in  the  indole 
molecule  is  as  follows: 


The  1 -substituted  derivatives  are  sometimes  termed  w-de- 
rivatives,  e.g.  %-methyl-indole,  C6H4<^pTT_^CH. 

Various  derivatives  may  be  obtained  synthetically  by  the 
condensation  of  the  aromatic  primary  or  secondary  hydrazines 
either  with  pyroracemic  acid  or  with  certain  ketones  or  alde- 
hydes, and  treatment  of  the  resulting  hydrazones  with  dilute 
hydrochloric  acid  or  zinc  chloride,  when  ammonia  is  eliminated 


622     XXXV.  CONDENSED  BENZENE,   FURANE,   ETC.   RINGS 
(E.  Fischer,  A.  236,  116:   242,   372);    thus  acetone  -phenyl- 

PIT 

hydrazone,   C6H5  .  NH  .  N  :  O^g3,   yields   a-  methyl  -indole, 
CH3,  propaldehyde  -  phenyl  -  bydrazone  yields 


skatole,  and  phenacyl  bromide  and  aniline  yield  a-phenyl- 
indole.  See  also  B.  25,  2860. 

Skatole,  3-methyl-indok,  C6H4<^Q^e~^>CH,  is  found  in  faeces, 

and  is  produced,  together  with  indole,  e.g.,  by  the  decay  of 
albumen,  or  by  fusing  it  with  potash.  It  crystallizes  in  colour- 
less plates  of  a  strong  faecal  odour  and  melts  at  95°.  Nitrous 
acid  does  not  colour  it  red.  It  takes  up  two  atoms  of  hydrogen 
to  form  a  hydro-compound.  Acids,  aldehydes,  &c.,  are  also 
known. 

Dioxindole,  CfiH4<£^QH^>CO,  or  the  lactam  of  o-amino 

mandelic  acid,  NH2.C6H4.CH(OH).C02H,  is  obtained  by  the 
reduction  of  isatin  (into  which  it  is  again  easily  oxidized)  with 
zinc  dust  and  hydrochloric  acid,  or  by  the  oxidation  of  oxin- 
dole.  It  crystallizes  in  colourless  prisms,  melts  at  180°,  and 
possesses  both  basic  and  acid  properties  (two  hydrogen  atoms 
being  replaceable);  it  also  forms  a  nitroso-  compound,  an 
N-acetyl  derivative,  &c. 

Oxindole,  C6H4<^QTT  ^>CO,  the  lactam  of  o-amino-phenyl- 

acetic  acid,  is  formed  by  the  reduction  of  0-nitro-phenyl-acetic 
acid  (p.  452);  also  by  that  of  dioxindole  with  tin  and  hydro- 
chloric acid.  It  crystallizes  in  colourless  needles,  melts  at  1  20°, 
is  readily  oxidized  to  dioxindole,  and  therefore  possesses  feebly 
reducing  properties.  Oxindole  is  amphoteric,  dissolving  both 
in  alkalis  and  in  hydrochloric  acid.  Baryta  water  at  a  some- 
what high  temperature  transforms  it  into  barium  0-amino- 
phenyl-acetate.  The  imino-hydrogen  is  exchangeable  for  ethyl, 
acetyl,  the  nitroso-group,  &c. 

Isomeric  with  oxindole  is  indoxyl,  CgHi^Vr    ^CH,  which 


is  obtained  by  the  elimination  of  carbon  dioxide  from  indoxylic 
acid,  a  product  formed  from  phenyl-glycocoll  (p.  452),  also  by 
fusing  indigo  with  potash.  It  is  often  present  in  the  urine  of 
the  carnivora  as  potassium  indoxyl-sulphate  or  urine-indican, 
C8H6N-0.(S03K).  It  forms  yellow  crystals,  melting  at  85°, 
is  moderately  soluble  in  water  with  yellow  fluorescence,  and 


iSATiN  523 

not  volatile  with  steam.  It  is  very  unstable,  quickly  becoming 
resinous,  and  is  readily  transformed  into  indigo  when  its  alka- 
line solution  is  exposed  to  the  air,  or  when  ferric  chloride  is 
added  to  its  solution  in  hydrochloric  acid. 

It  yields  a  nitroso-  compound,  C6H4<Qy'QjTw>CH,   of  the 

same  character  as  the  nitrosamines,  and  therefore  it  contains 
an  imino-group;  further,  its  relation  to  indoxyl-sulphuric  acid 
shows  that  it  contains  an  alcoholic  hydroxy-group,  and  thus 
its  constitution  follows. 

Potassium  indoxyl-sulphate  is  prepared  synthetically  by 
warming  indoxyl  with  potassium  pyrosulphate;  it  crystallizes 
in  glistening  plates  and  is  hydrolysed  when  warmed  with 


acids. 


Ethyl-indoxyl  is  obtained  from  indoxyl  by  the  exchange  of 
the  hydroxylic  hydrogen  for  C2H5.     Derivatives  of  the  hypo- 

thetical pseudo-  indoxyl,  C6H4<^QQj>CH2,  are  also  known, 

some  of  them  being  convertible  into  indigo  derivatives  (e.g. 
diethyl-indigo). 

Indoxylic   acid,   C6H4^^  •  C02H,   the   carboxylic 


acid  of  indoxyl,  forms  white  crystals,  is  oxidized  to  indigo  by 
ferric  chloride,  and  breaks  up  into  indoxyl  and  carbon  dioxide 
when  fused.  It  is  obtained  from  its  ester,  ethyl  indoxylate,  by 
fusing  with  soda.  The  latter  compound  crystallizes  in  stout 
prisms,  melts  at  120°,  and  may  be  obtained,  among  other 
methods,  by  the  reduction  of  ethyl  o-nitro-phenyl-propiolate 
with  ammonium  sulphide. 

PO 
Isatin,  C6H4<^TT^>CO,  the  lactam  of  o-aminp-benzoyl-formic 

acid  (p.  463),  is  readily  prepared  by  oxidizing  indigo  or  in- 
doxyl with  nitric  acid  (Erdmann  and  Laurent,  1841  ;  cf.  also 
B.  17,  976).  It  may  also  be  obtained  by  the  oxidation  of 
dioxindole  or  of  oxindole  (indirectly). 

The  following  are  among  some  of  the  most  important 
methods  by  means  of  which  isatin  has  been  synthesised:  — 

(a)  When  o-nitro-phenyl-glyoxylic  acid  (o-nitro-benzoyl- 
formic  acid,  p.  462)  is  reduced,  the  corresponding  amino-acid 
is  obtained;  but  this  immediately  loses  water,  yielding  a  lactam 
or  lactim  : 

mi 


524     XXXV.    CONDENSED  BENZENE,   FtTRANE,   ETC.   RINGS 

(b)  0-Nitro-phenylacetic    acid   when    reduced    yields    the 

lactam,  oxindole,  CfiH4<^XTT/^>CO,  and  this  with  nitrous  acid 

M.Mxi-^  P/«"NT  OT^ 

gives  the  iso-nitroso-oxindole,  06H4<i&T_        ;>CO,  which 

on  reduction  is  converted  into  amino-oxindole,  and  this  on 
oxidation  with  ferric  chloride  yields  isatin. 

(c)  Sandmeyer  has  worked  out  the  following  synthesis:  — 
Aniline  and  carbon  disulphide  readily  yield  thio-carbanilide, 
CS(NHC6H5}2,    which,    on    boiling   with    potassium   cyanide, 
white-lead,    and    water,    yields    hydrocyano-carbo-diphenyl- 
imide,  C6H5«N:C(CN).NHC6H5.     With  ammonium  sulphide 

this  latter  yields  ^\C|>C.NHC6H5,  which  is  con- 
verted by  concentrated  sulphuric  acid  into  a-isatin-anilide, 
C6H4<^jr  ^C'NHC6H5,  and  this  may  be  hydrolysed  by  dilute 

acids  to  isatin  and  aniline  (C.C.  1900,  2,  928). 

(d)  0-Nitrophenyl-propiolic  acid  (p.  456)  may  be  synthesised, 
and  when  this  is  warmed  with  alkalis  it  undergoes  molecular 
rearrangement  and  yields  isatogenic  acid,  which  by  elimi- 
nation of  carbon  dioxide  forms  isatin: 


Isatin  crystallizes  in  reddish-yellow  monoclinic  prisms,  which 
are  only  sparingly  soluble  in  cold  water,  but  more  readily  in 
hot  water  and  in  alcohol  to  a  brownish-red  solution.  It  dis- 
solves in  potassium  hydroxide  solution,  yielding  the  potassium 

derivative,  C6H4<^=^>C«OK,  which  is  readily  hydrolysed  to 
potassium  0-amino-phenyl-glyoxylate  when  boiled  with  water. 

/~^{~\ 

Isatin  chloride,  C6H4<^;^C.C1,  is  obtained  when  isatin  is 

heated  with  phosphorus  pentachloride,  and  on  reduction  with 
zinc  dust  and  acetic  acid  yields  indigo. 
Two  isomeric  methyl  ethers  are  known  : 


and 

O-methyl  isatin  N-methyl  isatin  or  pseudo-methyl  isatin. 

The  O-ether  is  obtained  by  converting  the  potassic-isatin 
into  the  silver  compound,  and  then  heating  this  with  methyl 


INDIGO  525 

iodiae.      It  is  a  colourless   solid   melting  at   102°,  and  on 
hydrolysis  yields  isatin  or  o-amino-phenyl-glyoxylic  acid. 

The  N-ether  may  be  obtained  by  the  action  of  sodic  hypo- 
bromite  on  N-methyl-indole.  Its  constitution  follows  from 
its  method  of  formation,  and  also  from  the  fact  that  on 
hydrolysis  it  yields  o  -  methyl  amino  -  phenyl-  glyoxy  lie  acid, 
T  /CO.CO2H 


The  constitution  of  isatin  itself  for  some  years  was  a  matter 
of  dispute;  from  its  method  of  formation  it  must  be  either  the 
lactam  or  lactim  of  o-amino-phenyl-glyoxylic  acid.  Certain 
of  its  methods  of  formation  and  of  its  reactions,  e.g.  with 
alkalis  or  phosphorus  pentachloride,  point  to  the  lactim  for- 
mula, whereas  others  would  indicate  the  lactam  constitution  — 
isatin  is  thus  a  typical  tautomeric  compound.  Hartley  and 
Dobbie  (J.  C.  S.  1899,  647)  assign  to  it  the  lactam  constitution. 
The  ultra-violet  absorption  of  alcoholic  solutions  of  isatin  is 
almost  identical  with  that  of  the  N-methyl  ether,  and  quite 
different  from  that  of  the  0-methyl  ether,  and  hence  the 
N-methyl  ether  and  the  parent  substance  have  similar  formulae. 
Isatin  is  thus  a  pseudo-acid,  since  the  hydrogen  compound 

itself  is  the  ketonic  substance,  C6H4<^p,Q^>COj  but  its  sodic 


derivative  is  the  enolic  compound, 

INDIGO  AND  RELATED  COMPOUNDS 
Indole  or  benzo-pyrrole 

Indoxyl  or  hydroxy-indole 

Oxindole  or  o-amino-phenyl-aceticl  n  -rr  /OH 
acid  lactam  ..........  .  .....  '  ..........  /C«H4\NB 

Dioxindole    or    o  -  amino  -  mandelic 

acid  lactam 
Isatin  or  o-amino-phenyl-glyoxylicl  ~  ,-,.  /  CO  \nr& 

acid  lactam  .....  _...L:......:..../C«H*\NH/ 

Indigo  .....................................   C6H4<^>C:C<^>C6H4. 

Indigo,  which  is  obtained  from  the  indigo  plant  (Indigofera 
tinctoria),  and  from  woad  (Isatis  tindoria),  has  been  known 
for  thousands  of  years  as  a  valuable  blue  dye,  especially  for 
woollen  fabrics.  In  addition  to  indigo  -blue  (indigotin), 


526      XXXV.   CONDENSED  BENZENE,   FURANE,   ETC.    RINGS 

commercial  indigo  contains  indigo-gelatine,  indigo-brown,  and 
indigo-red,  all  of  which  can  be  extracted  from  it  by  solvents. 
The  colouring  matter  is  not  present  as  such  in  the  indigo  plant, 
but  as  the  glucoside  of  indoxyl  "  Indican  ",  from  which  it  can 
be  prepared  either  by  dilute  acids  or  certain  enzymes  and  sub- 
sequent oxidation  with  atmospheric  oxygen. 

It  forms  a  dark-blue  coppery  and  shimmering  powder  or, 
after  sublimation,  copper-red  prisms,  insoluble  in  most  solvents 
(including  the  alkalis  and  dilute  acids),  but  dissolving  to  a 
blue  solution  in  hot  aniline  and  to  a  red  one  in  paraffin,  from 
either  of  which  it  may  be  crystallized.  Its  vapour  is  dark-red. 
The  formula  C16H1002N2  is  confirmed  by  its  vapour  density. 
It  is  converted  by  reducing  agents,  such  as  ferrous  sulphate 
and  caustic  soda  solution  or  grape-sugar  and  soda,  into  the 
leuco-compound,  indigo-white,  C16H1202N2,  a  white  crystalline 
powder  soluble  in  alcohol  and  ether,  also  in  alkalis  (as  a 
phenol);  the  alkaline  solution  quickly  becomes  oxidized  by 
the  oxygen  of  the  air,  with  the  separation  of  a  blue  film  of 
indigo.  It  yields  an  acetyl  compound  which  crystallizes  in 
colourless  needles. 

Warm  concentrated  or  fuming  sulphuric  acid  dissolves 
indigo  to  indigo  -monosulphonic  and  disulphonic  acids,  the 
former  of  which  (termed  phoenicin-sulphonic  acid)  is  sparingly 
soluble  in  water,  but  the  latter  readily  so;  the  sodium  di- 
sulphonate  is  the  indigo-carmine  of  commerce.  Nitric  acid 
oxidizes  indigo  to  isatin,  while  distillation  with  potash  yields 
aniline,  and  heating  with  manganese  dioxide  and  a  solution  of 
potash,  anthranilic  acid. 

Indigo  has  been  prepared  synthetically  by  numerous 
methods.  The  following  are  among  the  most  important:  — 

1.  By  the  reduction  of  isatin  chloride  with  zinc  dust  and 
acetic  acid: 


The  syntheses  of  isatin  already  described  (pp.  523  and  554) 
are  thus  syntheses  of  indigo. 

2.  By  warming  o-nitro-phenyl-propiolic  acid  with  grape-sugar 
in  alkaline  solution  (Baeyer,  1880): 

2N02.C6H4C:C.C02H  +  4H  =  C1GH10N2O2  +  2CO2  +  2H2O. 


3.  Baeyer  and  Drewson  (1882)  started  with  toluene,  and  on 
nitration  obtained  a  mixture  of  o-  and  j?-mtro-toluenes,     The 


INDIGO  527 

0-compound  was  oxidized  by  manganese  dioxide  and  sulphuric 
acid  to  0-nitro-benzaldehyde,  and  this  was  then  condensed 
with  acetone,  yielding  o-nitro-phenyl-lactyl  methyl  ketone, 

NO2  •  C6H4  •  CH(OH)  •  CH2  .  CO  •  CH3  ; 

which  when  warmed  with  alkalis  gave  indigo  and  water.  The 
yield  was  good,  but  the  method  was  of  no  great  practical 
importance,  as  the  amount  of  toluene  is  limited,  and  no  use 
could  be  found  for  the  ^?-nitro-toluene  obtained  as  a  by-pro- 
duct. 

4.  In   1890   Neumann   obtained   phenyl-glycocoll   by   the 
condensation  of  aniline  with  chloracetic  acid: 

—  C6H5.NH.CH2.CO2H, 


and  when  this  was  fused  with  alkali,  indigo-white  was  obtained. 

A  modified  form  of  Heumann's  synthesis  consists  in  con- 
densing anthranilic  acid  (p.  452)  with  chloracetic  acid,  when 
phenyl-glycocoll-o-carboxylic  acid  is  obtained,  and  this  on 
fusion  with  alkali  yields  indoxyl,  which  oxidizes  in  the  air 
to  indigo-blue.  The  yield  is  good,  and  this  method  is  now 
employed  on  a  manufacturing  scale  by  the  "Badische  Anilin 
Fabrik"  for  the  production  of  artificial  indigo,  as  anthranilic 
acid  can  be  obtained  cheaply;  the  general  method  being  the 
oxidation  of  naphthalene  by  mercury  and  sulphuric  acid  to 
phthalic  acid,  the  conversion  of  this  into  phthalic  anhydride, 
and  then  into  phthalimide  by  the  aid  of  ammonia.  The 
phthalimide  with  alkali  and  chlorine  yields  anthranilic  acid  — 
o-amino-benzoic  acid  (Hofmann  reaction,  p.  184). 

Homologues  of  indigo  are  produced  in  an  analogous  manner, 
and  its  sulpho-acids  by  the  action  of  fuming  sulphuric  acid 
upon  phenyl-glycocoll. 

Indigo-blue  is  one  of  the  best  of  the  blue  dyes,  on  account 
of  its  "  fastness  "  to  light,  alkalis,  acids,  and  soaps.  As  indigo- 
blue  itself  is  insoluble,  its  "  leuco  "  compound  indigo-white  is 
usually  employed,  the  fabric  being  immersed  in  an  alkaline 
solution  of  this,  and  then  exposed  to  the  air,  when  oxidation 
to  indigo-blue  takes  place.  Indigo-blue  is  usually  reduced  to 
indigo-white  by  means  of  calcium  hyposulphite.  The  indigo- 
white  is  a  colourless  solid  with  phenolic  properties,  and  probably 
has  the  constitution  represented  by  the  formula  — 


528  XXXVI.   PYRAZOLE  GROUP 

Iiidirubin,  Indigo-purpurin,  is  an  isomeride  of  indigo-blue, 
and  can  be  obtained  synthetically  by  the  condensation  of 
isatin  and  indoxyl  in  alkaline  alcoholic  solution: 


It  is  also  obtained,  together  with  indigo-blue,  by  the  reduc- 
tion of  isatin  chloride.  It  crystallizes  from  aniline  in  chocolate- 
brown  needles,  and  on  oxidation  yields  isatin. 

(For  history  and  manufacture  of  indigo,  see  /.  Ind.  1901, 
239,  332,  551,  802;  J.  C.  S.  1905,  974.) 


XXXVI.  PYKAZOLE  GROUP,  ETC. 
1.  PYRAZOLE  GROUP 

This  comprises  compounds  with  a  five-membered  ring  contain- 
ing three  carbon  and  two  nitrogen,  sulphur,  or  oxygen  atoms. 
Pyrazole,  aCH-N-v 

2     >NH, 


*CH:< 

5 

is  theoretically  derivable  from  pyrrole  in  the  same  way  aa 
pyridine  is  from  benzene,  i.e.  by  the  exchange  of  CH  for  N. 

The  positions  three  and  five  appear  to  be  identical  unless 
the  H  of  the  NH  is  replaced  by  alkyl  groups. 

It  is  a  weak  base  of  great  stability,  crystallizing  in  colour- 
less needles;  it  melts  at  70°,  boils  at  185°,  and  possesses  aro- 
matic properties  (B.  1895,  28,  714).  Its  simplest  synthesis  is 
by  the  union  of  acetylene  and  diazo-methane: 


HO       CHf  HC:CH 

(Van,  Pechmann,  B.  1897,  31,  2950).     (For  other  syntheses, 
see  B.  23,  1103;  A.  273,  214.) 

Pyrazoline,  C3H6N2,  and  pyrazolidine,  CgHgNg,  are  derived 
theoretically  from  pyrazole  by  the  addition  of  hydrogen.  By 
the  exchange  of  two  atoms  of  hydrogen  for  one.  of  oxygen,  the 
formula  of  pyrazole  changes  into  that  of  pyrazolone, 

CH  : 


THIAZOLE  529 

(an  oil,  b.-pt.  77°;  see  B,  25,  3441),  and  by  the  entrance  of 
phenyl  and  methyl  into  this  latter  we  get: 

l-Phenyl-3-methyl-pyrazolone,  which  is  obtained  by  the 
action  of  phenylhydrazine  on  ethyl  acetoacetate  (p.  230): 

CH,.CO  H2N  CHS.C:N 

CH,COOEt+      NHPh= 


This  crystallizes  in  compact  prisms,  melts  at  127°,  and  boils 
without  decomposition.  As  a  weak  base  it  dissolves  in  acids, 
and  is  also  soluble  in  alkalis;  it  further  contains  the  chemi- 
cally-active methylene  group.  When  it  is  heated  with  methyl 
iodide  and  methyl  alcohol  it  yields  : 

l-Phenyl-2:3-dimethyl-pyrazolone  or  antipyrine,  CnH12N2O, 
which  is  also  produced  by  the  action  of  ethyl  acetoacetate  upon 
methyl-phenyl-hydrazine,  and  which  therefore  possesses  the 
constitutional  formula  (L.  Knorr,  A.  238,  137), 

CMe-NMex 

L  :  .,       cH_co>ph-     (^ 

It  crystallizes  in  small  colourless  plates  melting  at  113°.  The 
aqueous  solution  is  coloured  red  by  ferric  chloride  and  blue- 
green  by  nitrous  acid.  Antipyrine  is  an  excellent  febrifuge. 
/3-Ketonic  acids,  /?-ketonic  aldehydes,  /3-diketones  also  yield 
pyrazole  derivatives  with  phenyl-hydrazine. 

Isomeric  with  pyrazole  is  glyoxaline  (p.  530),  in  which  the 
two  atoms  of  N  are  separated  by  a  C  atom. 

2.  THIAZOLE  GEOUP 
Thiazole, 


is  derived  from  thiophene  in  the  same  way  as  pyridine  is  from 
benzene,  by  the  exchange  of  CH  for  N,  and  closely  resembles 
—  along  with  its  derivatives  —  the  bases  of  the  pyridine  series 
in  properties.  It  is  obtained  from  amino-thiazole  (see  below) 
by  the  exchange  of  the  amino-group  for  hydrogen,  in  a  similar 
manner  to  the  conversion  of  aniline  into  benzene.  It  is  a 
colourless  liquid,  boiling  at  117°,  hardly  distinguishable  from 
pyridine;  as  a  base  it  forms  salts,  but  it  is  scarcely  affected  by 
concentrated  sulphuric  acid,  &c.  (Hantzsch,  Popp,  A.  250,  273). 

(B480)  2L 


530  XXXVI.    PYRAZOLE  GROUP 

Amino-tMazole, 


is  formed  by  the  action  of  mono-chloraldehyde  upon  thio-urea 
(pseudo  form),  thus: 


The  constitution  of  the  thiazoles  follows  from  this  and  similar 
modes  of  formation.  Amino-thiazole  is  a  base  of  perfect 
"  aromatic  "  character,  like  that  of  aniline.  (Cf.  Rantzsch  and 
his  pupils,  A.  249,  1,  7,  31;  250,  257;  265,  108.) 

As  further  types  of  five-membered  rings,  may  be  cited  : 


CH.N 

Imidazole  or  glyoxalin  Oxazole, 


which  are  related  to  thiazole  as  pyrrole  and  furane  are  tc 
thiophene. 


Triazole,  NH,  and  tetrazole, 


are  examples  of  five-membered  rings  extremely  rich  in  nitro- 
gen.    (Cf.  B.  25,  225,  1411;  26,  2392.) 

The  foregoing  constitutional  formula  with  their  double 
linkings  correspond  with  KekuU's  benzene  formula.  But  for- 
mulse  with  diagonal  (centric)  linkings  analogous  to  the  centric 
benzene  formula  (p.  334)  have  been  introduced  recently.  (Cf. 
Bamberger,  B.  24,  1758;  A.  273,  373;  also  A.  249,  1;  262,  265; 
B.  21,  Ref.  888;  24,  3485;  27,  3077;  28,  1501.) 


XXXVII.   SIX-MEMBERED  HETEROCYCLIC  RINGS 

Ring  compounds  closely  related  to  pyrrole,  thiophene,  and 
furane,  but  containing  six  atoms  in  the  ring  (viz.  five  carbon 
atoms  +  °ne  °xygen>  sulphur,  or  nitrogen  atom),  are  known. 

The     representatives     of    these     are :      8  -  valerolactone, 

glutaric   anhydride, 


y-PYRONE  531 

(p.   240),   and   more   especially   the   pyrones,   e.t\   y-pyrone, 


Of  the  nitrogen   compounds,  pyridine, 


and  piperidine,  CH2<^QTT2"pTT2^>NH,  are  of  great  importance. 
The   derivatives   of    the    sulphur   compound,    penthiophene, 

^^CH'CHX^'  are  °^  ^ut  ^^e  imP°rtance- 
Six-membered   rings  containing  two  nitrogen  atoms  are 
the  diazines,  C4H4N2,  the  ortho  compound  is.pyjidazine,  the 
meta  pyrimidine,    and    the    para  pyrazine.      The   compound, 


is   morpholin.     Six-membered   rings  con- 

fining three  and  four  nitrogen  atoms  are  termed  respectively 
triazines  and  tetrazines.     (Of.  triazole  and  tetrazole,  p.  530.) 

A.  Pyrones 

y-Pyrone,   a  solid,   m.-pt.    32-5°  and   b.-pt.    315°,   is   ob- 
tained when  its  dicarboxylic  acid,  chelidonic  acid  (p.  533),  is 

heated,   aa-dimethyl-y-pyrone,  C0<       !        ^'  may  be  syn" 


thesised  from  cupric  ethyl  aceto-acetate  and  carbonyl  chloride. 


(C02Et).CO.CH3 


p 
UuCH(C02Et).CO.CH 


On  hydrolysis  with  sulphuric  acid  the  ester  yields  the  free 
acid,  which  loses  carbon  dioxide,  yielding: 


CO.CHS    or   ™xCH:C(OH)C 


which  immediately  loses  water,  yielding  dimethyl-y-pyrone  : 


(For  a  modified  formula,  see  Collie,  J.  C.  S.  1904,  971.) 
Collie  and  Tidde  (J.  C.  S.  1899,  710)  have  shown  that  this  com- 
pound can  form  definite  salts  with  acids,  e.g.  the  hydrochloride, 
C7H8O2,  HC1,  and  oxalate.  The  addition  of  the  acid  un- 
doubtedly occurs  at  the  oxygen  atom,  since  the  salts  are 
relatively  unstable  and  are  completely  hydrolysed  in  dilute 
aqueous  solution.  The  oxygen  atom  in  these  salts,  therefore, 


532          XXXVII.   SIX-MEMBERED  HETEROCYCLIC   RINGS 

probably  functionates  as  a  tetravalent  atom,  [oXKci1  and 
the  salts  are  termed  oxonium  salts  on  account  of  their  simi- 
larity to  ammonium  salts.  Numerous  other  compounds  have 
since  been  obtained,  which  tend  to  show  that  the  oxygen 
atom  can  frequently  functionate  in  this  manner,  e.g.  numerous 
oxygen  compounds,  esters,  ethers,  ketones,  acids,  aldehydes 
yield  definite  crystalline  compounds  with  anhydrous  metallic 
salts,  e.g.  MgBr2  or  A1C18  (Walker,  J.  C.  S.  1904,  1106;  similar 
oxygen  compounds  also  form  well-defined  crystalline  salts  with 
complex  acids,  e.g.  ferrocyanic  acid  (Baeyer  and  Villiger,  B. 
1901,  34,  2679,  3612;  1902,  35,  1201);  and  lastly,  the  addi- 
tive compound  of  organo-magnesium  derivatives  with  ether 

are  probably  of  the  type,  c*ip>0<f gCHs.     Solutions  of  the 

oxonium  salts  have  exactly  the  properties  we  should  expect. 
Since  the  salt  is  derived  from  a  very  feeble  base  (solutions 
of  dimethyl-pyrone  are  very  feeble  conductors)  and  a  rela- 
tively strong  acid,  the  solution  should  be  highly  hydrolysed, 
and  should  give  a  strongly  acid  reaction.  That  the  hy- 
drolysis is  not  complete  in  the  case  of  a  moderately  con- 
centrated solution  of  the  picrate  has  been  shown  by  WHlden 
(B.  1901,  34,  4191),  who  compared  the  partition  coefficient  of 
picric  acid  between  water  and  benzene  both  with  and  without 
the  addition  of  dimethyl-pyrone,  and  found  that  the  ratio 
concentration  of  benzene  solution  ^  less  when  ^  is 

concentration  of  aqueous  solution 
present. 

Other  methods  which  have  also  led  to  the  conclusion  that 
a  certain  amount  of  salt  exists  in  solution  are  (a)  depression  of 
the  freezing-point  of  aqueous  solutions.  If  no  compound  exists 
in  an  aqueous  hydrochloric  acid  solution,  then  the  depression 
caused  would  be  the  sum  of  the  depressions  produced  by  the 
known  amounts  of  dimethyl-pyrone  and  hydrochloric  acid 
present.  The  actual  value  obtained  is  less  than  this  sum 
(Walderi).  (b)  A  determination  of  the  electrical  conductivity. 
If  no  compound  is  formed,  the  conductivity  should  be  the  same 
as  the  conductivity  of  a  solution  of  pure  hydrochloric  acid  of 
the  same  concentration;  but  if  any  appreciable  amount  of  a  salt 
is  formed  in  solution  this  will  give  rise  to  a  certain  number  of 

CrH8O2H  and  Cl,  i.e.  the  number  of  hydrions  will  be  less 
than  in  a  solution  of  pure  hydrochloric  acid  of  the  same 


PYRIDINE  533 

concentration,  and  hence  the  electrical  conductivity  will  be 
considerably  reduced.  It  has  actually  been  found  that  the 
conductivity  is  less,  and  that  it  tends  to  decrease  as  the  solution 
becomes  more  concentrated. 

y-Pyrone-dicarboxylic  acid,  or  chelidonic  acid,  occurs  in  the 
greater  celandine  (Chelidonium  majvs),  and  may  be  synthesised 
by  Claisen's  method  (p.  224).  Acetone  and  ethyl  oxalate  readily 
condense,  yielding  the  ester  of  acetone-dioxalic  acid  or  xantho- 
chelidonic  acid  : 

XCH3  ,  C02Et-C02Et  _  m/CH:C(C02Et)OH 
C02Et  .  C02Et  -    CU\CH  :  C(CO2Et)OH 


which  immediately  loses  water,  yielding  ethyl  chelidonate,  and 
this  on  careful  hydrolysis  yields  chelidonic  acid  : 


The  salts  of  this  acid  are  colourless,  but  when  it  is  warmed 
with  an  excess  of  alkali  yellow  salts  of  xantho-chelidonic  acid 
are  formed,  thus  indicating  the  readiness  with  which  the  ring 
is  ruptured. 

B.  Pyridine 

Pyridine,  C5H5N,  may  be  compared  with  benzene  in  many 
points : 

1.  It  is  even  more  stable  than  benzene,  and  does  not  yield 
substituted  derivatives  so  readily  with  such  reagents  as  sul- 
phuric and  nitric  acids  or  the  halogens.     Sulphonic  acids  are 
obtained  at  very  high  temperatures  only;  nitro-pyridines  are 
as  yet  unknown,  as  are  also  iodo-pyridines ;  while  chloro-  and 
bromo-pyridines  have  so  far  only  been  prepared  in  small  num- 
ber.    Neither  pyridine  nor  its  carboxylic  acids  are  affected  by 
nitric  acid,  chromic  acid,  or  permanganate  of  potash. 

2.  The  behaviour  of  its  derivatives  is  on  the  whole  very  like 
that  of  the  derivatives  of  benzene.     Thus  its  homologues  (and 
also  quinoline,  &c.)  are  transformed  into  pyridine-carboxylic 
acids  when  oxidized,  and  these  acids  yield  pyridine  when  dis- 
tilled with  lime,  just  as  benzoic  acid  yields  benzene. 

3.  The  isomeric  relations  are  also  precisely  analogous  to  those 
of  the  benzene  derivatives.     Thus  the  number  of  the  isomeric 
mono-derivatives  of  pyridine  is  the  same  as  that  of  the  isomeric 
bi-derivatives  of  benzene,  viz.,  three;  and  the  number  of  the 
bi-derivatives  of  pyridine,  containing  the  same  substituents,  the 
same  as  that  of  the  benzene  derivatives  C6H3XXX',  viz.,  six. 


534         XXXVII.   SIX-MEMBERED  HETEROCYCLIC  RINGS 

4.  Just  as  two  benzene  nuclei  can  form  naphthalene,  so  can 
a  benzene  and  a  pyridine  form  the  compound  quinoline : 


N. 


5.  The  products  of  reduction  are  likewise  analogous.  Pyri- 
dine like  benzene  yields  a  hexahydro-derivative,  C5HnN,  only 
somewhat  more  readily;  this  is  known  as  piperidine.  Quino- 
line yields  a  tetrahydro-derivative,  C9HnN,  more  readily  than 
naphthalene,  and  acridine  readily  yields  a  dihydro-derivative, 
C13HnN",  which  is  analogous  to  anthracene  dihydride.  In  these 
latter  compounds  further  combination  with  hydrogen  may  take 
place,  but  there  is  likewise  a  tendency  to  the  reproduction  of 
the  original  bases. 

We  are  therefore  forced  to  the  conclusion  that  pyridine  has 
a  ring  constitution  similar  to  that  of  benzene,  and  is  to  be 
represented  as: 

CH  CH 


HC 


CH 


HC 

^& 

N  N 

In  contradistinction  to  the  neutral  benzene  hydrocarbons, 
pyridine  and  its  homologues  are  strong  bases,  most  of  them 
having  a  pungent  odour;  pyridine  is  readily  soluble  in  water, 
but  quinoline  only  slightly  so.  They  distil  or  sublime  with- 
out decomposition,  and  form  salts;  those  with  hydrochloric 
and  sulphuric  acids  are  for  the  most  part  readily  soluble, 
while  those  with  chromic  acid  or  hydro -ferrocyanic  acid, 
though  often  characteristic,  are  usually  only  sparingly  soluble ; 
they  also  form  double  salts  with  the  chlorides  of  platinum, 
gold,  and  mercury,  most  of  which  are  sparingly  soluble,  e.g. 
(C5H5N)2H2PtCl6. 

The  bases  are  tertiary,  and  hence  cannot  be  acetylated; 
they  combine,  however,  with  alkyl  iodides,  yielding  quater- 
nary ammonium  salts,  e.g.  pyridine  and  methyl  iodide  yield 
C5H5N,  CH3I,  methyl-pyridonium  iodide. 

Pyridine  and  some  of  its  homologues  are  present  in  coal-tar, 
and  are  therefore  constituents  of  the  lower  boiling  fractions. 
They  may  be  extracted  from  these  by  shaking  with  dilute 


SYNTHESES  OF  PYRIDINE  DERIVATIVES  535 

sulphuric  acid,  in  which  they  dissolve.  It  is  also  present  in 
tobacco  smoke.  A  number  of  pyridine  bases  are  present  in 
bone-oil  or  Dippel's  oil,  a  product  obtained  by  £fee  dry  distil- 
lation of  bones  from  which  the  fat  has  not  been  extracted. 

Mixtures  of  pyridine  bases  can  readily  be  obtained  from 
this  source.  Certain  alkaloids  4Hfc^  7)  yield  pyridine  or  its 
derivatives  when  distilled  alone^r  with  alkalis,  e.g.  chincho- 
nine  when  distilled  with  potash  yields  a  dimethyl-pyridine 
or  lutidine.  Pure  pyridine  may  be  obtained  by  distilling  its 
carboxylic  acid  with  lime. 

Among  the  more  interesting  methods  by  means  of  which 
pyridine  and  its  derivatives  have  been  synthesised  are  the 
following  :  — 

1.  When  pentamethylene-diamine  hydrochloride  is  strongly 
heated  it  yields  piperidine,  and  when  this  is  oxidized  with 
concentrated  sulphuric  acid  at  300°  pyridine  is  formed  (Laden- 
burg): 

•  CH2 

2.  |NH2 


A  method  very  similar  to  this,  which  can  be  employed  at 
much  lower  temperatures,  is  the  elimination  of  hydrogen 
chloride  from  5-chloroamylamine,  CH2C1'(CH2)3'CH2«NH2. 
This  elimination  occurs  when  an  aqueous  solution  of  the  base 
is  heated  on  the  water-bath;  ring  formation  takes  place,  and 
piperidine  hydrochloride  is  formed  (Gabriel).  These  two 
methods  are  of  great  importance  in  deciding  the  constitution 
of  piperidine,  and  therefore  indirectly  that  of  pyridine. 

2.  The  ammonia  derivatives  of  various  unsaturated  aldehydes 
yield  pyridine  homologues  when  distilled  (p.  130),  e.g.  /3-methyl- 
pyridine  is  obtained  from  acrolein  ammonia,  and  collidine  from 
croton-aldehyde  ammonia  (Baeyer,  A.  155,  283,  297). 

3.  When  ethyl  acetoacetate  is  warmed  with  aldehyde-am- 
monia, the  ester  of  "  Dihydro-collidine-dicarboxylic  acid",  ie. 
ethyl  trimethyl-dihydro-pyridine-dicarboxylate  is  produced 
(Hantzsch)  (cf.  p.  230): 

CO2Et-CH2      O-CHMe      CH2.CO2Et 

MeCO    "        NH3      "^COMe 

C02Et  -  C  —  CHMe  —  C  -  CO2Et 

~~  3H2    +  CMe-NH.MeC 


636          XXXVII.   SIX-MEMBEREt)  IIETEfcOCYCLIC  RINGS 

This  loses  its  two  "hydro  "-hydrogen  atoms  when  acted 
on  by  nitrous  acid,  and  yields  ethyl  collidine-dicarboxylate, 
C5N(CH3)3(C02Et)2,  from  which  collidine  may  be  obtained  by 
hydrolysis  and  elimination  of  carbon  dioxide. 

If,  instead  of  aldehyde-ammonia,  the  ammonia  compounds 
of  other  aldehydes  are  uitf&  homologous  bases  of  the  type 
C5H2N(CH3)2(CnH2ntl)  are~rmed. 

In  the  above  reaction  a  molecule  of  the  acetoacetic  ester  may 
be  replaced  by  one  of  an  aldehyde,  when  the  mono-carboxylic 
esters  of  dialkylated  pyridines  are  formed,  thus  : 

C6H10O3  +  2CH3.CHO  +  NH3  =  C6H2NH2(CH3)2.C02Et  -f  3H2O. 

This  is  a  very  important  synthetical  method  (Hantzsch, 
A.  215,  1,  &c.). 

Two  methods  of  obtaining  pyridine  derivatives,  which  indi- 
cate the  relationship  of  pyridine  to  quinoline  and  pyrrole,  are  : 

(a)  The  conversion  of  quinoline  into  quinolinic  acid  or  pyri- 
dine a/3-dicarboxylic  acid  (p.  544). 

(b)  The  conversion  of  potassium-pyrrole  into  chloro-pyridine 
when  heated  with  chloroform,  or  into  pyridine  when  heated 
with  methylene-chloride: 


CH:CH\  CHiCH-N  CH:CH.N 

CH:CH/  CH-.CH-CCl  °r  CH:CH.CH 


Not  merely  is  the  ring  constitutional  formula  (p.  534)  in 
perfect  harmony  with  the  characteristic  properties  of  pyridine 
and  its  derivatives,  and  also  with  certain  of  the  synthetical 
methods  of  formation,  but  this  formula  receives  additional 
support  from  a  study  of  the  number  of  isomeric  forms  in 
which  pyridine  derivatives  occur. 

Three  isomeric  mono-  substituted  derivatives  of  pyridine 
are  known  in  each  case.  They  are  designated  as  a-,  /?-,  and 
y-derivatives  of  pyridine,  as  is  shown  in  the  following  graphic 
formula  : 


or  as  2-,  3-,  or  4-derivatives  according  to  the  numbering 
p.  534. 


on 


PYRIDINE  537 

In  order  to  determine  the  position  of  any  given  group,  it  is 
sought  to  exchange  it  for  carboxyl;  should  picolinic  acid  result, 
the  group  occupies  the  a-position,  and  should  nicotinic  or  iso- 
nicotinic,  then  it  fills  the  fi-  or  y-position  respectively,  since 
in  these  acids  the  a-,  /?-,  and  y-positions  of  the  carboxyl  have 
been  determined  by  special  means.  (See  M.  1,  800;  4,  436, 
453,  595;  B.  17,  1518;  18,  2967;  19,  2432.) 

Di-derivatives  of  pyridine  containing  the  same  substituent 
twice  can  exist  theoretically  in  six  isomeric  forms.  As  a 
matter  of  fact  the  six  dicarboxylic  acids  are  known  (aa  -,  a/3-, 
ay-,  ap-t  /?y-,  and  ftp-  (see  p.  538). 

The  isomerism  of  picoline,  C6H^N,  with  aniline,  C6H5«NH2, 
which  repeats  itself  in  their  homologues,  is  also  worthy  of 
notice. 

Pyridine,  C5H5N  (Anderson,  1851),  may  be  prepared  from 
bone-oil,  and  can  be  obtained  pure  by  heating  its  carboxylic 
acid  with  lime;  the  ferrocyanide  is  especially  applicable  for 
its  purification,  on  account  of  its  sparing  solubility  in  cold 
water.  It  is  also  found  in  the  ammonia  of  commerce. 
Pyridine  is  a  liquid  of  very  characteristic  odour,  miscible 
with  water,  and  boiling  at  115°.  It  is  used  as  a  remedy  for 
asthma,  and  also  in  Germany  for  mixing  with  spirit  of  wine 
in  order  to  render  the  latter  duty-free.  When  sodium  is 
added  to  its  hot  alcoholic  solution,  or  when  solutions  of  its 
salts  are  electrolysed,  hydrogen  is  taken  up  and  piperidine, 
CglLjN,  formed  (Ladenburg  and  Both,  B.  17,  513). 

When  heated  strongly  with  hydriodic  acid,  pyridine  is 
converted  into  normal  pentane. 

The  ammonium  iodides,  e.g.  C5H5N,  CH3I,  give  a  character- 
istic pungent  odour  when  heated  with  potash,  a  fact  which 
may  be  made  use  of  as  a  test  for  pyridine  bases;  it  depends 
upon  the  formation  of  alkylated  dihydro-pyridines,  e.g.  di- 
hydro-methyl-pyridine,  C5H6.N(CH3)  (Hofmann,  B.  14,  1497). 

Pyridine  is  polymerized  by  the  action  of  metallic  sodium 
to  dipyridine,  C10H10N2  (an  oil,  b.-pt.  286°-290°),  with  the 
simultaneous  production  of  ^-dipyridyl,  C5H4N  •  C5H4N  (long 
needles,  m.-pt.  114°),  a  compound  corresponding  to  diphenyl 
(p.  471);  both  of  these  yield  iso-nicotinic  acid  when  oxidized. 
An  isomeric  m-dipyridyl  has  also  been  prepared,  which  gives 
nicotinic  acid  when  oxidized. 

Pyridine  can  be  brominated  but  not  nitrated;  it  can  also  be 
sulphonated  with  the  formation  of  /2-pyridine-sulphonic  acid, 
C&H4N  •  (S03H),  which  with  potassium  cyanide  yields  /?-cyano- 


638          XXXVII.    SIX-MEMBERED  HETEROCYCLIC  RINGS 

pyridine,  C5H4N-CN,  or  by  fusion  with  potash,  fthydroxy- 
pyridine. 

The  three  hydroxy-pyridines,  C5H4N(OH)  (a-,  ft,  y-),  are 
best  prepared  by  the  elimination  of  carbon  dioxide  from  the 
respective  hydroxy-pyridine-carboxylic  acids.  The  melting- 
points  are  respectively:  a,  107°;  ft  124°;  y,  148°.  They  pos- 
sess the  character  of  phenols,  and  are  coloured  red  or  yellow  by 
ferric  chloride.  As  in  the  case  of  phloroglucinol,  so  here  also 
there  is  a  tertiary  as  well  as  a  secondary  form  to  be  taken 
into  account,  the  former  reminding  one  of  the  lactams  and  the 
latter  of  the  lactims;  for  instance,  y-hydroxy-pyridine  may 


either  have  the  "phenol"  formula  C2H2<C2H2  or  the 

p*o 
"pyridone"  formula  C2H2<^jj^>C2H2,  the  latter  of  the  two 

representing  a  keto-dihydro-pyridine.  The  two  methyl  ethers, 
methoxy-  pyridine  and  methyl  -pyridone,  which  result  from 
these  two  forms  by  the  exchange  of  H  (of  the  OH  or  NH 
respectively)  for  CH3,  are  both  known,  and  differ  considerably 
in  properties  (M.  6,  307,  320;  B.  24,  3144). 

Homologues  of  Pyridine  (cf.  Ladenburg,  A.  247,  1).  — 
Methyl-pyridines  or  picolines,  C5H4N(CH3).  All  the  three 
picolines  are  contained  in  bone-oil,  and  probably  also  in  coal- 
tar.  The  ftcompound  is  obtained  from  acrolein-ammonia 
(p.  130),  and  also  when  strychnine  is  heated  with  lime,  or 
when  trimethylene-diamine  hydrochloride  is  distilled.  They 
are  liquids  of  unpleasant,  piercing  odour  resembling  that  of 
pyridine,  and  they  yield  a-,  ft,  or  y-pyridine-carboxylic  acid 
when  oxidized.  The  boiling-points  are:  a,  129°;  ft  142°, 
y,  142°-144°. 

Ethyl-pyridines,  C5H4N(C2H5),  are  also  known. 

Propyl-  and  isopropyl  pyridines,  C5H4N(C3H7),  have  been 
carefully  investigated  on  account  of  their  relation  to  coniine. 
They  are  prepared  by  heating  pyridine  with  the  alkyl  iodides. 
Conyrine,  C8HnN  (liquid,  b.-pt.  166°-168°),  which  is  formed 
when  coniine,  CgH^N,  is  heated  with  zinc  dust,  and  which 
yields  coniine  again  when  treated  with  hydriodic  acid,  is 
a-normal-propyl-pyridine. 

a-Allyl-pyridine,  C5H4N(C3H5),  is  produced  when  a-picolino 
is  heated  with  aldehyde  : 

C6H4N.CH34-OHC-CH3  =  C6H4N.CH:CH.CH3  +  H2O. 

Reduction  transforms  it  into  inactive  coniine  (b.-pt.  189°-190  ). 


PYRIDINE  CARBOXYLIC  ACIDS  539 

Bimethyl-pyridines  or  Lutidines,  C5H3N(CH3)2. — The  pre- 
sence of  three  lutidines  has  been  proved  in  bone-oil  and  coal- 
tar  (B.  21,  1006;  29,  2996).  ay-Lutidine  boils  at  157°,  the 
aa'-compound  at  142°,  and  the  /ty-compound  at  164°. 

The  trimethyl-pyridines  or  collidines,  C5H2N(CH3)3,  are 
isomeric  with  the  propyl-pyridines.  Some  of  them  are  pre- 
sent in  bone-oil,  and  can  be  prepared  from  cinchonine  by  dis- 
tilling the  latter  with  caustic  potash  (p.  560).  The  aa'y-colli- 
dirie,  which  is  obtained  from  the  condensation  product  of 
ethyl  acetoacetate  and  aldehyde  ammonia  (p.  230),  boils  at 
171°-172°. 

Pyridine-carboxylic  Acids  (Weber,  A.  1887,  241,  1).— The 
pyridine-mono-carboxylic  acids,  C5H4N(C02H),  are  formed 
by  the  oxidation  of  all  mono-alkyl  derivatives  of  pyridine, 
i.e.  from  methyl-,  propyl-,  phenyl-,  &c.,  pyridines;  also  from 
the  pyridine-dicarboxylic  acids  by  the  decomposition  of  one  of 
the  carboxyl  groups,  just  as  benzoic  may  be  got  from  phthalic 
acid.  The  carboxyl  which  is  in  closest  proximity  to  the  nitro- 
gen is  the  first  to  be  eliminated.  Nicotinic  acid  is  also  pro- 
duced by  the  oxidation  of  nicotine.  The  acids  unite  in  them- 
selves the  characters  of  the  basic  pyridine  and  of  an  acid,  and 
are  therefore  comparable  with  glycocoll.  They  yield  salts  with 
HC1,  &c.,  and  double  salts  with  HgCl2,  PtCl4,  &c.;  on  the  other 
hand,  they  form  metallic  salts  as  acids,  those  with  copper  being 
frequently  made  use  of  for  the  separation  of  the  acids. 

(For  constitution,  see  Skraup  and  Colenzl,  M.  1883,  4,  436.) 

The  a-acid  is  picolinic  acid,  and  forms  needles  melting  at 
135°. 

The  /?-acid  is  nicotinic  acid,  and  melts  at  231°. 

The  y-acid  is  iso-nicotinic  acid,  and  melts  at  309°  in  a  sealed 
tube. 

It  is  noteworthy  that  all  three  acids  (and  also  the  /3y-dicar- 
boxylic  acid)  readily  yield  up  their  nitrogen  as  ammonia  when 
acted  upon  by  sodium  amalgam,  being  thereby  transformed 
into  unsaturated  acids  of  the  fatty  series  (Weidel,  M.  1890, 
11,  501). 

The  constitution  of  nicotinic  acid  follows  from  its  relation- 
ship to  quinoline.  Quinoline  on  oxidation  yields  pyridine 
a/2-dicarboxylic  acid,  the  constitution  of  which  follows  from 
the  constitution  of  quinoline.  When  heated,  the  dibasic  acid 
loses  carbon  dioxide,  yielding  a  monobasic  acid  which  is  not 
identical  with  picolinic  acid  (which  can  be  shown  to  be  the 
a-acid),  and  therefore  it  must  be  pyridine  /2-carboxylic  acid. 


540          XXXVII.   SIX-MEMBERED  HETEROCYCLIC  RINGS 

Pyridine-dicarboxylic  acids,  C5H3N(C02H)2 

a-j8-  =  Quinolinic  acid M.-pt.  190°. 

0-7-  =  Lutidinic  acid M.-pt.  235°. 

a-a'-  =  Dipicolinic  acid M.-pt.  226°. 

a-j3'-  =  Iso-cinchomeronic  acid M.-pt.  236°. 

/S-j8'-  =  Dinicotinic  acid. . . .  .* M.  -pt.  323°. 

(3-y-  =  Cinchomeronic  acid M.-pt.  266°. 

Quinolinic  acid,  which  crystallizes  in  short  glistening  prisms, 
is  the  analogue  of  phthalic  acid,  and  is  obtained  by  the  oxi- 
dation of  quinoline,  just  as  phthalic  acid  from  naphthalene; 
cinchomeronic  and  iso-cinchomeronic  acids  are  obtained  by  the 
oxidation  of  cinchonine  and  quinine. 

Hydro-pyridines. — According  to  theory,  hexa-,  tetra-,  and 
dihydro-pyridines  may  exist.  The  first  of  these  receive  the 
generic  name  of  "  piperidines ",  e.g.  pipecoline,  C5H10N(CH3), 
lupetidine,  C5H9N(CH3)2,  and  copellidine,  C5H8N(CH3)3;  while 
the  tetrahydro-compounds  are  termed  "  piperideins  ". 

Piperidine,  CgH^N  (Werftitim,  Eochleder,  1850),  is  a  colour- 
less liquid  of  peculiar  odour,  slightly  resembling  that  of  pepper, 
and  of  strongly  basic  properties  yielding  crystalline  salts.  It 
dissolves  readily  in  water  and  alcohol,  and  boils  at  106°. 

It  occurs  in  pepper  in  combination  with  piperic  acid, 
C12H1004  (p.  464),  in  the  form  of  the  alkaloid  piperine, 
C18H]8N08  =  C§H10N  •  C12H903,  i.e.  piperyl-piperidine,  which 
crystallizes  in  prisms,  melting  at  129e;  from  this  latter  it  may 
be  prepared  by  boiling  with  alkali. 

(For  its  formation  from  pyridine  and  from  pentamethylene- 
diamine,  see  pp.  196,  535,  537.) 

Piperidine  is  a  secondary  amine;  its  imino-hydrogen  is 
replaceable  by  alkyl  and  acyl  radicals.  When  its  vapour, 
mixed  with  that  of  alcohol,  is  led  over  zinc  dust,  homologous 
(ethylated)  piperidines  are  formed. 

When  methylated,  piperidine  yields,  as  a  secondary  base,  in 
the  first  instance,  tertiary  n-methyl-piperidine,  CgHj  0N(CH3), 
and  then  with  a  further  quantity  of  methyl  iodide  an  ammo- 
nium iodide,  dimethylpiperidonium  iodide.  The  correspond- 
ing hydroxide  does  not  decompose  in  the  usual  manner  when 
distilled,  but  yields  water  and  an  aliphatic  base,  "dimethyl- 
piperidine",  07H16N  or  CH2:CH.CH2-CH2.CH2.NMe2. 

The  latter  forms*  a  quaternary  iodide,  the  hydroxide  of 
which,  when  distilled,  gives  trimethylamine  and  piperylene, 
CHMe:CH-CN:CH2  (exhaustive  methylation.  For  further 
examples,  see  Chap,  on  Alkaloids). 


QUINOLINE  AND  ACRIDINE  GROUPS 


541 


XXXVIII.   QUINOLINE  AND  ACKIDINE  GROUPS 

A.  Quinoline  Group 

The  quinoline  group  comprises  the  compounds  formed  by 
the  condensation  of  a  benzene  nucleus  with  a  heterocyclic  six- 
membered  ring.  The  best-known  examples  are: 

O 


Chromone  (benzene  +  pyrone  rings), 


Quinoline  (benzene  +  pyridine), 


Iso-quinoline  (benzene  +  pyridine), 


1.  CHROMONE  GROUP 

Chromone, — Chromone  itself  melts  at  59°  (Buhemann  and 
Stapletwi,  J.  C.  S.  1900,  1185),  and  the  phenyl  derivative, 

/O— C-C6H5 

flavone,   C6HX         ••          ,   is   the   parent  substance  of  a 
\OO  •  GH 

number  of  yellow  dyes  which  occur  in  the  vegetable  kingdom. 
Most  of  these  dyes  are  hydroxylic  derivatives  of  flavone,  and 
occur  in  nature  in  the  form  of  glucosides. 

As  examples  we  have  Chrysin  (dihydroxy-flavone),  Luteolin 
(5:7:3':4'-tetrahydroxy-flavone,  Kostanedi,  Abstr.  1901,  1,  92, 
335),  Quercitin  (3:5:7:3':4'-pentahydroxy-flavone,  Herzig,  M. 
1885,  6,  872),  Rhamnetin  (3:5:3':4'-tetrahydroxy-7-methoxy- 
flavone),  and  Rhamnazm  (3:5:4'-trihydroxy-7:3'-dimethoxy- 
flavone,  Perkin  and  Allison,  J.  C.  S.  1902,  469). 


642  XXXVIII.   QUINOLINE  AND  ACRIDINE  GROUPS 

The  constitution  of  these  compounds  is  often  arrived  at 
by  an  examination  of  the  products  formed  by  the  action  of 
alcoholic  potash  on  the  compound,  or,  more  readily,  by  aspi- 
rating air  through  the  dilute  alkaline  solution;  under  these 
conditions  rhamnetin  yields  protocatechuic  acid,  3:4-dihydroxy- 
benzoic  acid  (p.  459),  and  phloroglucinol  monomethyl  ether. 

2.   QUINOLINE  AND  ITS  DERIVATIVES 

Quinoline, 


bears  the  same  relationship  to  naphthalene  that  pyridine  does 
to  benzene,  its  molecule  consisting  of  condensed  benzene  and 
pyridine  nuclei.  It  occurs,  together  with  derivatives,  in  both 
coal-tar  and  bone-oil,  and  may  be  obtained  by  heating  certain 
alkaloids  with  potash,  e.g.  cinchonine  yields  quinoline  itself 
(Gerhardtj  1842),  and  quinine  gives  methoxy-quinoline. 

Among  the  various  syntheses  of  quinoline  and  its  deriva- 
tives the  following  may  be  noted:  — 

1.  The  first  synthesis,  which  was  accomplished  by  Koenigs, 
was  by  the  oxidation  of  allyl-aniline  by  passing  its  vapour 
over  heated  lead  oxide: 


C6H6.NH.CH2.CH:CHa  +  20  =  C^  +  2H/X 

2.  One  of  the  usual  methods  employed  for  the  preparation 
of  pure  quinoline  is  by  Skraup's  synthesis  (B.  14,  1002).  In 
this  process  aniline  is  heated  with  glycerol  and  sulphuric  acid 
in  presence  of  nitro-benzene  or  arsenic  acid  : 

OH.CH2.CH  -OH 
+  CH8.OH 

The  nitro-benzene  simply  acts  as  an  oxidizing  agent.  The 
formation  of  acrolein  as  an  intermediate  product  is  to  be 
assumed  here,  the  latter  combining  in  the  first  instance  with 
aniline  to  acrolein-anilme,  C6H5  •  N  :  CH  •  CH  :  CH2.  The  homo- 
logues  and  analogues  of  aniline  yield  homologues  and  ana- 
logues of  quinoline  by  corresponding  reactions;  when  naph- 
thylamine  is  used,  the  more  complicated  naphtho-quinolines 
are  formed. 


SYNTHESES   OF  QUINOLINE  DERIVATIVES  543 

3.  Baeyer  and  Drewson  (B.  16,  2207)  obtained  quinoline  by 
the  elimination  of  the  elements  of  water  from  0-amino-cinnamic 
aldehyde : 

::CH-CHO  _  /CH:CH 

If  0-amino-cinnamic  acid   is  used,  carbostyril  (a-hydroxy- 
quinoline,  p.  546)  is  obtained  (Baeyer): 

TFT 

+  H20. 

4.  When  aniline  is  heated  with  aldehyde  (paraldehyde)  and 
hydrochloric  acid,  a-methyl-quinoline  (quinaldine)  is  obtained 
(Doebner  and  v.  Miller). 

In  this  reaction  ethylidene-aniline  is  formed  as  an  inter- 
mediate product  (B.  24,  1720;  25,  2072): 


OCH.CH3 

Aniline  Quinaldine. 

Here,  again,  various  other  primary  arylamines  may  be  used 
instead  of  aniline,  and  other  aldehydes  (B.  18,  3361)  or  ketones 
(e.g.  B.  19,  1394)  instead  of  paraldehyde. 

5.  Aniline  and  acetoacetic  acid  combine  together  at  tem- 
peratures above  110°  to  aceto-acetanilide,  CH3 -CO  .CHACO- 
NS'CgR^  from  which  y-methyl-a-hydroxy-quinoline  ("methyl- 
carbostyril ")  is  formed  by  the  elimination  of  water  (Knorr,  A. 
1886,236,75): 

CH3 •  CO  •  OH2  yv/^OJEijj) : OH 

C6H6.NH-CO  6    4\N  =  C-0 

Aniline  can  also  react  with  acetoacetic  ester  below  100°, 
yielding  ethyl  /2-phenyl-amino-crotonate,  C6H5.NH.C(CH3): 
CH  •  COgCgH*,  which  yields  y-hydroxy-quinaldine  when  heated 
(Conrad  and  Limpach,  B.  20,  944): 

C2H6O.CO.CH  /C(OH):CH 

C6H5.NH.C.CH3  4\N=C.CH3  T 

/3-Diketones  and  other  compounds  closely  related  to  aceto- 
acetic ester  also  condense  with  aniline.  In  place  of  /5-di- 
ketones,  mixtures  of  ketones  and  aldehydes,  or  mixtures  of 
aldehydes  which  would  yield  /3-diketones  or  /3-ketonic  alde- 
hydes if  condensed  together  (C.  Beyer,  B.  20,  1767),  can  be 


544  XXXVIII.    QUINOLINE  AND  ACRIDINE  GROUPS 

employed.     With  acetyl-acetone  we  obtain  ay-dimethyl-quino- 
line  (B.  1899,  32,  3228): 


These  reactions  are  nearly  allied  to  those  already  spoken  of 
under  4. 

6.  0-Amino-benzaldehyde  condenses  with  aldehydes  and 
ketones  under  the  influence  of  dilute  caustic  soda  solution, 
yielding  quinoline  derivatives  (Friedldnder,  B.  15,  2574;  16, 
1833;  25,  1752).  With  aldehyde  quinoline  itself  results,  and 
with  acetone  quinaldine  : 

/CHO      CH2.E 
C«H<NH2+CO.B<    ! 

Acetophenone,  acetoacetic  ester,  malonic  ester,  diketones, 
&c.,  also  react  in  a  similar  way. 

Constitution.  —  The  above  modes  of  formation  (especially  3 
and  6)  show  that  quinoline  is  an  ortho-di-substituted-derivative 
of  benzene,  and  that  it  contains  its  nitrogen  linked  directly  to 
the  benzene  nucleus;  they  also  show  that  the  three  carbon 
atoms,  which  enter  the  complex,  form  a  new  hexagon  (pyri- 
dine)  ring  with  this  nitrogen  and  with  two  carbon  atoms  of 
the  benzene  ring.  The  latter  point  also  follows  from  the 
oxidation  of  quinoline  to  pyridine-dicarboxylic  acid  (Hoogewerff 
and  van  Dorp]  : 


Quinoline  Quiuolinic  acid. 

We  have  thus  the  following  constitutional  formula: 

N  o  N 


according  to  which  quinoline  is  constituted  in  a  manner  per- 
fectly analogous  to  naphthalene,  and  may  be  regarded  as 
derived  from  the  latter  by  the  exchange  of  CH  for  N,  or  as 
formed  by  the  "condensation"  of  a  pyridine  and  a  benzene 
nucleus. 


QUINOLINE  DERIVATIVES  545 

When  quinoline  derivatives  are  oxidized,  the  benzene  ring 
is  usually  more  readily  ruptured  than  the  pyridine  one,  e.g. 
quinoline  yields  pyridine-dicarboxylic  acid  (p.  540).  a-Methyl- 
quinoline  gives,  on  the  other  hand,  0-acetyl-amino-benzoic  acid 
when  oxidized: 


(For  laws  governing  the  oxidation  of  quinoline  derivatives, 
see  W.  v.  Miller,  B.  23,  2252;  24,  1900;  M.  1891,  12,  304.) 

The  pyridine  nucleus  of  quinoline  takes  up  hydrogen  more 
readily  than  the  benzene  one;  thus  quinoline  is  easily  con- 
verted, even  by  tin  and  hydrochloric  acid,  into  tetrahydro- 
quinoline.  It  can  be  further  reduced  to  the  deca-hydride,  but 
only  with  difficulty. 

The  three  hydrogen  atoms  of  the  pyridine  nucleus,  counting 
from  the  N,  are  designated  as  a-,  ft-,  and  7-,  and  the  four  hy- 
drogen atoms  of  the  benzene  nucleus  as  0-,  m-,  p-,  and  a-  (ana-) 
hydrogen  atoms,  or  more  commonly  the  numbering  shown 
above  is  adopted,  the  nitrogen  atom  being  numbered  1  and 
the  carbon  atoms  consecutively  2,  3,  &c.,  up  to  8.  As  no  two 
hydrogen  atoms  are  symmetrically  situated  in  the  molecule, 
seven  mono-substituted  derivatives  of  quinoline  are  in  each 
case  theoretically  possible.  As  a  matter  of  fact,  all  seven 
quinoline-monocarboxylic  acids  have  been  prepared. 

The  position  of  the  substituents  follows  :  (a)  from  the  nature 
of  the  oxidation  products,  e.g.  B-quinoline-carboxylic  acid  (i.e. 
an  acid  in  which  the  carboxyl  is  attached  to  the  benzene 
nucleus)  yields  a  pyridine-dicarboxylic  acid,  while  a  Py-quino- 
line-carboxylic  acid  (in  which  the  carboxyl  is  linked  to  the 
pyridine  nucleus)  yields  a  pyridine-tricarboxylic  acid;  (b)  from 
the  synthesis  of  the  compound  in  question.  The  methyl- 
quinoline,  for  instance,  which  is  obtained  from  o-toluidine  by 
the  Skraup  synthesis  must  be  the  8-methyl-quinoline  : 

/y\ 

+  C3H6(OH)3  +  0  =  +4H20, 

NH2  \/\/ 

CH3  CH3  N 

whilst  m-toluidine  must  yield  a  7-  or  5-,  and  ^-toluidine  a 
6-methyl-quinoline. 

Quinoline  (Eunge,  1834)  is  a  colourless  strongly  refracting 
liquid  of  a  peculiar  and  very  characteristic  odour.  It  boils  at 

(9480)  2M 


546  XXXVIII.   QUINOLINE  AND  ACRIDINE  GROUPS 

239°,  is  a  mono-acid  base,  forms  a  sparingly  soluble  dichromate, 
(C9H7N)2,  H2O207,  and  is  used  as  an  antifebrile.  As  a  tertiary 
base  it  yields  quinolonium  salts  (Boser,  A.  1893,  272,  221). 

Nascent  hydrogen  transforms  it  first  into  dihydro-quinoline, 
CQHQN,  which  melts  at  161°,  and  then  into  tetrahydro-quinoline, 

/CH  «CH 
C9HUN,  =  C6H/ *'  -    *  a  liquid  boiling  at  245°.     Since 

NJN  ±1  •  \ja-2 

both  of  these  yield  nitrosamines  and  can  be  alkylated,  they  are 
secondary  bases.  The  tetrahydro-compound  exerts  a  stronger 
antifebrile  action  than  the  mother  substance,  especially  in  the 
form  of  its  ethyl  derivative,  cairolin  (B.  16,  739). 

Quinoline  decahydride,  CLK^N,  is  obtained  when  strong 
reducing  agents  are  employed.  It  forms  crystals  of  a  narcotic, 
coniine-like  odour,  melts  at  48°,  and  boils  at  204°. 

Halogen  derivatives  of  quinoline  and  nitro-quinolines  have 
been  prepared  by  the  Skraup  reaction,  &c.;  and,  from  the 
reduction  of  the  latter,  amino-quinolines,  C9H6N(NH2).  The 
quinoline-sulphonic  acids  yield  cyano-quinolines  with  potassium 
cyanide,  and  hydroxy-quinolines  when  fused  with  potash. 

l-Hydroxy-quinoline,  carbostyril,  is  a  quinoline  hydroxylated 
in  the  pyridine  nucleus  (see  p.  543,  mode  of  formation  3).  It 
crystallizes  in  colourless  needles,  melts  at  198°,  and  is  soluble 
in  alkali,  from  which  it  is  again  thrown  down  by  carbonic 
acid.  Its  constitution  follows  from  its  formation  from  o-amino- 
cinnamic  acid  (p.  456). 

Quinaldine,  2-methyl-quinoline,  C10H9N,  is  contained  in  coal- 
tar.  It  is  a  colourless  liquid  of  quinoline  odour,  and  boils  at 
246°.  When  oxidized  with  chromic  acid  it  yields  a  quinoline 
derivative,  with  permanganate  a  pyridine-tricarboxylic  acid. 

The  hydrogen  of  the  methyl  group  readily  enters  into  re- 
action; quinaldine  reacts  with  phthalic  anhydride  to  produce 
a  beautiful  yellow  dye,  quinoline-yellow,  C1QH7N(CO)2C6H4 
(B.  16,  2602).  A  mixture  of  quinoline  and  quinaldine  is 
transformed  into  the  (unstable)  blue  dyes,  the  cyanines,  when 
alkylated  and  treated  with  caustic  potash.  These  are  used  as 
sensitizers  for  photographic  plates. 

ftuinoline-carboxylic  Acids. — All  the  seven  quinoline  mono- 
carboxylic  acids,  which  are  possible  according  to  theory,  are 
known.  Quinoline-benz-carboxylic  acids  are  those  which  con- 
tain the  carboxyl  group  in  the  benzene  nucleus. 

Cinchoninic  acid,  guinolineA-carloxylic  acid,  C9H6N(CO2H), 
which  is  obtained  by  the  oxidation  of  cinchonine  with  per- 


ISO-QUINOLINE  547 

manganate  of  potash,  crystallizes  in  needles  or  prisms  and 
melts  at  254°.  From  it  is  derived  quinic  acid,  §-methoxy- 
quinoline-i-carloxylic  acid,  C9H5N(OCH8)  •  C02H,  which  is  ob- 
tained by  oxidizing  quinine  with  chromic  acid;  it  forms  yellow 
prisms,  melting  at  280°. 

Quinoline-2  :  3-dicarboxylic  acid,  or  acridinic  acid,  is  formed 
by  the  oxidation  of  acridine. 

3.  ISO-QUINOLINE 

Iso-quinoline,  an  isomer  of  quinoline,  occurs  along  with  the 
latter  in  coal-tar  (B.  18,  Ref.  384).  It  is  a  solid,  melts  at  23°, 
and  boils  at  240°.  Since  oxidation  converts  it  into  cincho- 
meronic  acid  on  the  one  hand  and  phthalic  acid  on  the  other, 
it  possesses  the  constitution  : 


Its  constitution  also  follows  from  its  synthesis*  from  homo- 

PTT      /~i/~\  TT 

phthalic  acid,  C6H4<^2A     2    ,  in  which  the  substituents 


are  in  the  o-position.     This  may  be  converted  into  its  imide. 

PTT      p/-w 

C6H4<^       2   •     ,  by  heating  the  ammonium  salt.     This  imide 

M30  —  NH 
with    phosphorus    oxychloride    reacts    as    the    tautomeride, 

/CH=C(OH) 
CgB^f  •         ,  and  yields  the  corresponding  dichloro- 

iso-quinoline,  which   is   reduced   by  hydriodic  acid  and  red 
phosphorus  to  iso-quinoline. 

B.  The  Acridine  Group 

Acridine,  C13H9N  (Graebe  and  Caro),  is  a  basic  constituent  of 
the  crude  anthracene  of  coal-tar,  and  also  of  crude  diphenyl- 
amine.  It  crystallizes  in  colourless  needles,  may  be  sublimed, 
and  is  characterized  by  an  intensely  irritating  action  upon  the 
epidermis  and  the  mucous  membrane,  and  also  by  the  greenish- 
blue  fluorescence  shown  by  dilute  solutions  of  its  salts. 

Acridine  stands  in  the  same  relationship  to  anthracene  that 
pyridine  does  to  benzene  or  quinoline  to  naphthalene.  It  may 

*For  synthesis  from  /3-naphthaquinone  see  B.  25,  1138,  1493;  27,  198; 
and  for  synthesis  from  benzylaminoacetaldehyde  hydro-chloride  and  sul- 
phuric acid  see  E.  Fischer,  B.  26,  764. 


548  XXXVIII.   QTJINOLINE  AND  ACRIDINE  GROUPS 

be  regarded  as  anthracene  in  which  one  of  the  CH-groups  of 
the  middle  ring  is  replaced  by  N.    This  constitutional  formula : 


is  based  (a)  upon  the  oxidation  of  acridine  to  qumoline- 
2  :  3-dicarboxylic  acid,  and  to  pyridine  tetracarboxylic  acid  — 
the  ^-union  between  C  and  N  becomes  ruptured  during  the 
oxidation;  (b)  upon  its  synthesis  from  diphenylamine  and 
formic  acid,  or  formyl-diphenylamine,  (C6H5)2N  •  CHO,  with 
zinc  chloride  (Bernthsen,  A.  224,  1): 
O 

-T    I'll 


a 


Formyl-diphenylamine  Acridine. 

It  is  also  obtained  when  the  vapour  of  0-tolyl-aniline  is  passed 
through  a  red-hot  tube. 

Acridine  is  a  tertiary  base,  and  as  such  combines  with  alkyl 
iodides,  yielding  acridonium  iodides.  It  is  a  much  feebler 
base  than  quinoline,  and  on  reduction  readily  forms  a  dihydro- 
derivative,  which  is  not  basic. 

Methyl-  and  butyl-acridines,  phenyl-acridine, 

C6H4« 

and  naphtho-acridines  (i.e.  acridines  which  contain  C10H6 
instead  of  C6H4)  have  all  been  prepared  synthetically  in 
an  analogous  manner. 

Diamino  -  dimethyl  -  acridine,  acridme  yellow,  C13H5(CH3)2 
(NH2)2N,  a  yellow  basic  dye,  is  formed  by  condensing  formic 
aldehyde  with  m-toluylene-diarnine,  splitting  off  ammonia,  and 
oxidizing  the  leuco-base  produced. 

The  chrysaniline  orphosphin  of  commerce,  a  beautiful  yellow 
dye,  is  diamino-phenyl-acridine,  C]9HnN(NH2)2,  since  it  yields 
phenyl-acridine  when  its  diazo  -  compound  is  boiled  with 
alcohol. 

Acridine  is  therefore,  like  anthracene,  a  chromogene. 


The  oxygen  analogue  of  dihydro-acridine,  C6H6< 
is  diphenylene-methane  oxide,  C6H4<_o£>C6H4,  which  can 


XXXIX.   AZINE,   ETC.   GROUP  640 

be  prepared  synthetically  and  also  by  distilling  euxanthone 
over  zinc  dust.  It  crystallizes  in  plates,  and  melts  at  9  8  '5°. 
It  is  on  the  one  hand  the  mother  substance  of  xanthone, 


4,  and  its  derivative  euxanthone  or  dihydroxy- 
xanthone,  OH  •  C6H3<^>C6H3  •  OH,  and  on  the  other  hand, 

of  the  rhodamines  and  fluoresceins  (p.  493).  Its  tetramethyl- 
diamino-  derivative  results  from  the  condensation  of  formic 
aldehyde  with  dimethyl  -  m  -  amino  -  phenol  to  tetramethyl- 
diamino-dihydroxy-diphenyl-methane  and  subsequent  elimi- 
nation of  water  (ring  formation),  and  is  the  leuco-compound 
of  formo-rhodamine  or  pyronine,  C17H19N2OC1,  into  which  ifc 
passes  upon  oxidation  and  production  of  quinoid  linking,  thus; 

/C6H,.N(CH3)2  /} 

H2C/        >0  HC/        >0 

XC6H3.N(CH3)2  XH3:N( 

Leuco-compound  Formo-rhodamine  hydrochloride. 


XXXIX.  SIX-MEMBERED  HETEROCYCLIC  COM- 
POUNDS WITH  NOT  MORE  THAN  FOUR 
CARBON  ATOMS  IN  RING.  AZINES,  ETC, 

A  number  of  six-membered  heterocyclic  compounds,  con- 
taining four  carbon  and  two  other  atoms,  are  known,  e.g.  par- 
oxazine,  with  4C,  10,  and  IN,  the  0  and  N  in  the  ^-position. 


A  derivative  of  this  is  morpholine,  0<g2*g2>NH.     Simi- 

larly, thiazines  (4C,  IS,  IN)  and  diazines  (4C,  2N)  are 
known;  and  these  are  the  parent  substances  of  numerous 
important  dyes.  The  majority  of  these  dyes  are  not  simple 
derivatives  of  oxazines,  thiazines,  or  diazines,  but  are  derived 
from  condensed  benzene  and  oxazine,  or  benzene  and  diazene 
nuclei,  and  may  be  compared  with  anthracene.  For  example, 
phenazine  is  anthracene  in  which  two  CH-groups  have  been 
replaced  by  two  N-radicals: 
CH  N 


Anthracene  Pheuazine 


650  XXXIX.   SIX-MEMBERED  AZINE  GROUP 

dihydro-phenazine  corresponds  with  dihydro-anthracene,  and 
phenoxazine  with  dihydro-anthracerie  in  which  one  CH2  has 
been  replaced  by  0  and  another  by  NH,  e.g.  : 

(I)  C6H<^>C6H4     (H)  CeH^J^CeH,     (III)  CeH^g^CeH, 

Dihydro-phenazine  Phenoxazine  Phentluazine 

(thio-diphenyl  amine). 

Further,  the  benzene  nuclei  may  be  replaced  by  those  of 
naphthalene,  with  the  formation  of: 


(IV)  C10H6<C10Hfl        (Y)  C10H6<(    >C6H4 

Naphthazine  Naphtho-phenoxazine. 

The  compounds  (I-III)  of  the  type  of  dihydro-anthracene 
are  the  leuco-compounds  of  dyes  when  they  contain  an  amino- 
(alkyl-amino-)  or  hydroxy-group  in  the  ^ara-position  to  the 
nitrogen.  The  dyes  themselves  are  obtained  from  these  by 
oxidation  (i.e.  elimination  of  hydrogen),  so  that  they  are 
derived  from  amino-  or  hydroxy-phenazines.  In  this  way  the 
eurhodines  (mon-amino-compounds)  and  the  toluylene  red  dyes 
(diamino-compounds)  are  derived  from  phenazine  and  hydro- 
phenazine,  and  similarly  the  safranines  and  indulines;  Nile 
blue  is  derived  from  naphtho-phenoxazine;  and  the  thionine 
dyes  from  phenthiazine. 

THE  DIAZINES 

The  three  simple  diazines  are  : 


:CH 

Pyridazine.  Pyrimidine.  Pyrazine. 

Pyridazine  is  a  colourless  liquid,  b.-pt.  208°,  is  miscible  with 
water,  has  an  odour  of  pyridine,  and  forms  soluble  salts. 
(Preparation,  cf.  B.  28,  451.) 

Pyrimidine  can  be  obtained  from  barbituric  acid  and  from 
methyluracil  (p.  287);  it  forms  colourless  crystals,  m.-pt.  22° 
and  b.-pt.  124°.  The  pyrimidme  ring  is  met  with  in  uric  acid 
and  in  most  purine  derivatives  (cf.  B.  34,  3248). 

Pyrazine  forms  colourless  prisms,  m.-pt.  47°,  b.-pt.  118°,  and 
is  basic  (J.  pr.  [ii],  51,  449).  Dimethylpyrazine,  Ketin,  is 
present  in  crude  amyl  alcohol,  and  can  be  obtained  by  the 
reduction  of  isonitrosoacetone  or  by  condensation  of  amino- 


fHENAZINES  51 

acetone.  Tetraphenylpyrazine  is  readily  obtained  from  ben- 
zoin. 

Of  the  compounds  formed  by  the  union  of  a  benzene 
and  a  diazine  nucleus  the  most  important  is  quinoxaline, 

C6H4^       •     ,  which  is  obtained  from  0-phenylene-diamine  and 
\N  I  C/rl 

glyoxal.  Substituted  quinoxalines  are  formed  by  condensing 
tt-dike  tones,  a-ketonic  acids,  &c.,  with  0-phenylene-diamines. 
Of  more  importance  is  the  group  of  compounds  containing 
two  benzene  nuclei  condensed  with  one  diazine  ring,  e.g. 
phenazine. 

Phenazine,  or  azo-phenylene  (p.  549),  is  obtained  by  the  dis- 
tillation of  barium  azo-benzoate,  or  by  leading  the  vapour  of 
aniline  through  red-hot  tubes;  also  from  nitrobenzene,  aniline, 
and  sodium  hydroxide  at  140°,  or  by  the  oxidation  of  its 
hydro-compound  (see  below).  It  crystallizes  in  beautiful, 
long,  bright-yellow  needles  melting  at  171°,  and  can  be  readily 
sublimed.  It  is  only  sparingly  soluble  in  alcohol,  but  readily 
in  ether,  and  also  dissolves  in  concentrated  sulphuric  acid  to  a 
red  solution;  the  alcoholic  solution  yields  a  green  precipitate 
on  the  addition  of  stannous  chloride.  When  reduced  with  am- 
monium sulphide  it  yields  the  colourless  hydro-compound,  di- 
hydro-phenazine,  C12H1002,  which  may  be  obtained  syntheti- 
cally by  heating  catechol  with  0-phenylene-diamine: 


The  entrance  of  hydroxy-  or  ammo-groups  into  these  azines 
converts  them  into  dyes.  In  accordance  with  modern  views  of 
the  quinonoicl  structure  of  dyes  these  derivatives  are  usually 
given  ortho  or  para  quinonoid  formulae  : 

Para,  C6H4<*J=>C6H3:NH;    ortho,  C6H4<g>C6H3.NH2, 

and  similarly  for  hydroxy  derivatives. 

The  amino-compounds  are  usually  termed  Eurhodines,  and 
may  be  obtained  by  condensing  arylamines  with  o-amino-azo- 
compounds. 

Eurhodine,  amino-naphtho-tolazine, 

or    CH3.C0H3<N2H>C10H6:NH, 


obtained  from  a-naphthylamine  and  0-amino-azo-toluene,  forms 
lustrous  golden  crystals  and  yields  scarlet  salts  (B.  19,  441 


552  XXXIX.    SIX-MEMBERED   PHENAZINE  GROUP 

21,  2418;  24,  1337).  When  heated  with  concentrated  hydro- 
chloric acid  it  is  converted  into  the  basic  and  at  the  same  time 
phenolic  compound  eurhodol, 

HO.C10H6<N2>C0H3.CH3    or    CH3.C6H3<N2H>C10H6:0 

(cf.  B.  24,  1337). 

0-Diamino-phenazine,  C12HgN3(NH2)2,  is  obtained  by  the 
oxidation  of  0-phenylene-diamine  with  ferric  chloride  (B.  22, 
355),  and  is  the  parent  substance  of  the  important  dyes  of  the 
toluylene  red  group.  When  a  mixture  of  ^-phenylene-diamine 
and  m-toluylene-diamine  is  oxidized  in  the  cold,  the  beautiful 
blue  compound,  toluylene  blue,  an  indamine  (p.  434),  is  formed, 
which  is  further  oxidized  to  toluylene  red,  diamino-tolu-phen- 
azine,  when  boiled  : 

NH2.C6H4.NH2  +  NH2.C6H3Me.NH2  +  20 

=  NH2  •  C6H4  •  N  :  C6H2Me(NH2)  :  NH  +  2  H2O 
NH2.C6H4.N:C6H2Me(NH2):NH  +  O 

=  NH2  •  C6H3<>C6H2Me  •  NH2  +  H20. 


This  diamino-tolu-phenazine  is  the  simplest  of  the  toluylene 
reds,  and  its  constitution  follows  from  the  fact  that  when 
diazotized  it  yields  methyl-phenazine.  Analogous  dyes  are 
neutral  red,  the  hydrochloride  of  dimethyl-diamino-tolu-phen- 
azine,  NMe2.C6H3<N2^C6H2MeNH2,  HC1,  and  neutral  violet, 
dimethyl  -diamino-pheriazine  hydrochloride.  The  leuco-  com- 
pounds are  the  corresponding  derivatives  of  dihydropheriazine. 

The  group  of  dyes  known  as  the  safranines  are  related  to 
toluylene  red.  They  are  amongst  the  oldest  of  the  aniline 
dyes,  and  include  mauve,  the  first  dye  prepared  by  W.  H. 
Perkin,  Senr.,  in  1856.  The  simplest  member  of  this  group 

is  pheno-safranine,  NH:C6H3<^^>C6H3.NH2,  which  is  of 

historical  interest  only.      The  dye   safranine  is   the   hydro- 
chloride  of  dimethyphenosafranine  : 


2\/%NPhClX\/ 


SAFRANINES  553 

I.  represents  the  compound  with  a  paraquinonoid,  and  II. 
with  an  orthoquinonoid  structure. 

The  commercial  product  is  usually  a  mixture  of  this  with  a 
homologue  containing  the  0-tolyl  group  in  place  of  the  Ph. 
The  method  of  manufacture  consists  in  the  oxidation  of  mole- 
cular proportions  of  j?-toluylene-diamine  and  0-toluidine  to  the 
corresponding  indamine,  and  then  the  condensation  of  this 
with  o-toluidine  to  give  the  tolu-safranine.  It  can  be  used  for 
cotton  mordanted  with  tannin,  and  gives  red  colours. 

The  safranines  are  beautiful  crystalline  compounds  of  a 
metallic  green  lustre,  readily  soluble  in  water,  and  dye  yel- 
lowish-red, red,  and  violet.  The  solution  in  concentrated  sul- 
phuric acid  is  green,  becoming  blue,  violet,  and  finally  red  on 
dilution  with  water.  Reduction  gives  rise  to  leuco-compounds, 
which  are  diamino-compounds  of  the  as  yet  unknown  substance 


H4  (B.    19,   2690,  3017,  3121;  29,  361, 

1442,  1870,  &c.);  treatment  with  nitrous  acid  and  alcohol 
yields  phenyl-phenazonium  chloride.  The  safranines  are  there- 
fore diamino-compounds  of  phenyl-phenazonium  chloride: 


Numerous  other  safranines  are  manufactured.  Methylene 
violet  is  asymmetric  dimethyl  -  safranine  chloride;  sqfranine, 
MN,  is  a  dimethyl-tolyl-safranine  chloride;  and  amethyst  violet, 
tetramethyl- safranine  chloride.  Parkin's  mauve  has  the  for- 
mula: 


Ph 


The  aposafranines  are  analogous  to  the  safranines,  but  con- 
tain only  one  amino-  or  substituted  amino-group,  and  at  least 
one  naphthalene  residue  in  place  of  a  benzene  ring.  They  are 
divided  into  Eosindulines  and  Isorosindulines.  The  former  con- 
tain the  amino  group  attached  to  the  naphthalene  ring  and 
give  red  shades,  the  latter  contain  the  amino  group  attached 
to  a  benzene  ring  and  give  blue  or  green  shades. 

Safranines  can  be  diazotized  and  coupled  with  alkaline 
solutions  of  /?-naphthol.  Indoin  blue  is  the  hydrochloride  of 
safranine-azo-naphthol,  C20H1GN3  •  N  :  N  •  C10H6OH,  HC1. 


554  XL.   ALKALOIDS 

PHENOXAZINES  AND  PHENTHIAZINES 

Phenoxazine  (p.  550)  is  obtained  by  heating  catechol  with 
o-aminophenol,  and  crystallizes  in  plates.  The  leuco-corapound 
of  nile  blue  is  a  diethyldiamino-naphthaphenoxazin.  The  dye 

itself,  NH:C10H5<Q>C6H4.NEt2,  HC1,  obtained  by  heating 

the  nitroso-derivative  of  diethyl-w-aminophenol  with  a-naph- 
thylamine,  is  a  brilliant  green-blue  basic  dye. 

Methylene  blue,  NMe2<C6H8<g>C6H3:NMe2Cl,  a  valuable 

blue  dye  for  wool,  is  formed  by  the  action  of  ferric  chloride 
on  amino-dimethylaniline  and  carbon  disulphide.  With  nitrous 
acid  it  yields  methylene  green. 

For  constitution  cf.  Kehrmann,  B.  39,  914;  Hantzsch,  ibid. 
1365. 


XL.   ALKALOIDS 

The  group  of  alkaloids  at  one  time  comprised  the  whole  of 
the  nitrogenous  basic  compounds  present  in  plants  or  derived 
from  the  various  plant  tissues  by  distillation.  Thus  methyl- 
amine,  betaine,  asparagine,  caffeine,  and  the  opium  alkaloids 
were  all  grouped  together,  but  as  their  constitutional  formulae 
were  established  they  were  grouped  with  the  compounds  to 
which  they  were  closely  related,  e.g.  methylamine  with  the 
primary  aliphatic  amines,  betaine  with  the  alkyl  derivatives  of 

flycocoll,  and  caffeine  with  the  uric  acid  or  purine  derivatives, 
'he  name  is  now  largely  restricted  to  the  nitrogenous  basic 
plant  constituents  which  can  be  regarded  as  derived  from  pyri- 
dine,  quinoline,  or  iso-quinoline,  and  to  those  of  unknown 
constitution. 

They  form  an  extremely  important  group  of  compounds  on 
account  of  their  physiological  properties,  and  they  constitute 
the  active  principles  of  the  common  vegetable  drugs  and 
poisons. 

With  a  single  exception  they  occur  exclusively  in  dicotyle- 
dons, and  as  a  rule  do  not  exist  in  the  free  state,  but  combined 
with  organic  acids  in  the  form  of  salts.  Such  acids  are  malic 
(p.  247),  citric  (p.  261),  and  tannic  (p.  460);  quinic  acid  usually 
accompanies  the  alkaloids  of  opium. 

A  few  of  the  alkaloids  are  built  up  of  carbon,  hydrogen,  and 


ALKALOIDS  555 

nitrogen,  e.g.  coniine,  nicotine.  Such  compounds  as  a  rule  are 
liquids  and  are  readily  volatile;  the  majority,  on  the  other 
hand,  contain  in  addition  oxygen,  and  then  are  usually  crystal- 
line and  non-volatile.  All  are  optically  active,  and  as  a  rule 
laevo-rotatory.  A  few  like  coniine  are  secondary  bases,  but 
the  majority  are  tertiary,  and  a  few  quaternary  ammonium 
compounds. 

The  following  reagents  as  a  rule  precipitate  the  alkaloids  in 
the  form  of  complex  derivatives  from  solutions  of  their  salts, 
viz.  tannin,  phosphomolybdic  acid,  a  potassium  iodide  solution 
of  iodine,  and  also  potassium  mercuric  iodide.  They  are 
further  characterized  by  their  bitter  astringent  taste  and  by 
their  poisonous  properties.  Each  individual  alkaloid  gives 
characteristic  colour  reactions. 

The  alkaloids  are  usually  extracted  from  plant  tissues  by 
lixiviating  the  finely-divided  tissue  with  acidified  water.  The 
extract  is  then  rendered  alkaline  with  ammonia  and  the  free 
alkaloid  separated  by  filtration,  or,  if  it  is  at  all  readily  soluble, 
by  extraction  with  chloroform. 

For  relationship  between  constitution  and  physiological 
properties  see  P.  May,  "  The  Chemistry  of  Synthetic  Drugs  ", 
London,  1911. 

The  structural  formula  for  an  alkaloid  is  usually  determined 
by  a  study  of  its  more  important  chemical  reactions  and  of  its 
degradation  products.  Among  the  reactions  generally  studied 
are: — 

1.  Determination  of  the  number  of  free  hydroxyl  groups  by 
acetylation  (cf.  p.  201).     Thus  morphine  can  be  shown  to  con- 
tain two,  codeine  one,  and  papaverine  none. 

2.  Determination  of  methoxy  groups  by  Zeisel's  method  or 
Perkin's  modification.     Papaverine  contains  four  such  groups, 
narcotine  three  and  codeine  one. 

3.  Study  of  the  action  of  hydrolysing  agents.     Esters  are 
hydrolysed,  but  most  other  types  of  linking  are  resistent  to 
such  agents.    Narcotine  (p.  561)  yields  opianic  acid  and  hydro- 
cotarnine,  and  is  presumably  an  ester  derived  from  these  two 
compounds.     Similarly,  atropine  (p.  565)  on  hydrolysis  yields 
tropic  acid  and  tropine.     As  the  products  of  hydrolysis  are 
simpler  than  the  original  alkaloid,  the  elucidation  of  their 
constitutions  is  less  difficult. 

4.  Examination  of  bhe  products  of  oxidation.    Thus  codeine 
contains  a  secondary  alcoholic  group,  as  on  oxidation  it  yields 
a  ketone,  codeinone,  containing  the  same  number  of  carbon 


556  XL.  ALKALOIDS 

atoms.  Coniine  when  oxidized  yields  pieolinic  acid,  and  must 
thus  be  an  a-  substituted  derivative  of  pyridine.  Cinchonine 
yields  quinoline-y-carboxylic.  acid. 

5.  Determination  of  the  primary,  secondary,  tertiary,  or 
quaternary  nature  of  the  base. 

6.  Study  of  the  degradation  products  obtained  by  exhaus- 
tive methylation.     As  an  example  of  this  method  the  simple 
secondary  amine  piperidine  may  be  taken.     When  methylated 
by  means  of  methyl  iodide  it  yields  first  the  tertiary  amine 
methylpiperidine,  and  finally  the  quaternary  ammonium  iodide, 
dimethylpiperidonium  iodide.     This  with  moist  silver  oxide 
yields  the  quaternary  base,  which  on  distillation  decomposes 
into  water  and  an  unsaturated  aliphatic  tertiary  amine: 


=  H2O  f  CH2:CH.CH2.CH2.CH2.NMe2. 

When  methylated  and  treated  with  silver  oxide  this  un- 
saturated base  yields  a  quaternary  hydroxide,  which  splits 
up  into  water,  trimethylamine,  and  AaS  pentadiene  when  dis- 
tilled: 


7.  An  examination  of  the  products  obtained  by  fusing  the 
alkaloid  with  potash  or  by  distilling  it  with  zinc  dust.  Thus 
morphine  and  zinc  dust  yield  phenanthrene  together  with 
other  products,  and  hence  the  molecule  of  morphine  probably 
contains  a  phenanthrene  ring.  Papaverine,  when  fused  with 
potash,  yields  dimethoxy-iso-quinoline  and  3:4-dimethoxy- 
toluene,  and  hence  papaverine  is  probably  an  iso-quinoline 
derivative.  The  processes  of  fusion  with  potash  and  distilla- 
tion with  zinc  dust  require  high  temperatures,  and  as  molecular 
rearrangements  occur  much  more  readily  at  high  than  at  low 
temperatures,  the  conclusions  drawn  from  a  study  of  the 
products  formed  during  such  processes  shonld  be  accepted 
with  a  certain  amount  of  reserve  unless  supported  by  other 
evidence. 

The  alkaloids  can  be  grouped  according  to  their  origin,  e.g. 
the  opium  alkaloids,  bases  from  solanine,  &c.,  or  according  to 
the  heterocyclic  ring  which  they  contain.  The  latter  method 
is  adopted  here,  and  we  thus  have  the  pyridine,  quinoline,  iso- 
auinoline,  and  phenanthrene  groups. 


PYRIDINE  ALKALOIDS  557 

A.  Alkaloids  derived  from  Pyridine 

Coniine,  dextro-rotatory  a-normal-pi'opyl-piperidine,  C5H10N 
(C3H7),  is  the  poisonous  principle  of  hemlock  (Conium  macu- 
latum).  It  is  a  colourless  dextro-rotatory  liquid  of  stupefying 
odour,  sparingly  soluble  in  water,  and  boils  at  167°.  Hy- 
driodic  acid  at  a  high  temperature  reduces  it  to  normal  octane, 
while  nitric  acid  oxidizes  it  to  butyric  acid,  and  potassium 
permanganate  to  picolinic  acid  (hence  the  a-position). 

Ladenburg  has  prepared  it  synthetically  by  reducing  a-allyl- 
pyridine  (p.  538)  in  alcoholic  solution  by  means  of  sodium 
(B.  19,  2578): 

C5H4N(C3H6)  +  8H  =  C6H10N(C3Hr). 

The  pyridine  ring  is  reduced  to  a  piperidine  ring,  and  at 
the  same'  time  the  unsaturated  allyl  side-chain  is  reduced  to  a 
%-propyl  group.  The  a-carbon  atom  is  an  asymmetric  carbon 
atom,  i.e.  it  is  attached  to  four  different  monovalent  radicals, 
and  the  whole  molecule  is  asymmetric.  The  synthetical  pro- 
duct is  optically  inactive,  and  thus  differs  from  the  natural 
product,  but  it  has  been  resolved  by  fractional  crystallization 
of  the  d-tartrate  into  dextro-coniine  and  a  laevo-coniine.  The 
relations  of  these  two  bases  to  one  another  and  to  the  inactive 
modification  are  the  same  as  that  of  dextro-  to  laevo-tartaric 
acid  and  to  racemic  acid. 

Nicotine,  C1pH14N?,  is  the  poisonous  constituent  of  the 
tobacco  plant,  in  which  it  exists  in  combination  with  malic 
and  citric  acids.  It  is  a  colourless,  oily  liquid  soluble  in 
water,  and  is  Isevo-rotatory.  It  rapidly  oxidizes  in  contact 
with  the  air,  and  boils  at  247°.  It  is  a  di-tertiary  base,  and 
therefore  readily  combines  with  methyl  iodide.  On  oxidation 
with  permanganate  it  yields  nicotinic  acid,  and  hence  must  be 
a  ^-pyridine  derivative.  It  has  been  synthesised  recently  by 
Pictet  (C.  E.  1903,  137,  860),  and  been  shown  to  be  a-pyridyl- 
N-methyl-pyrrolidine : 

OH, -OH, 


The  method  of  synthesis  is  as  follows: — Nicotinic  acid  is 
transformed  first  into  its  ethyl  ester,  and  then  into  the  amide; 


558  XL.    ALKALOIDS 

this  with  bromine  and  alkali  (Hofmann's  reaction,  pp.  107,  183) 
gives  /?-amino-pyridine,  and  when  the  salt  of  this  base  with 
mucic  acid  (p.  259)  is  distilled,  N-pyridyl-pyrrole, 


N</CH:CH 


is  formed.  When  the  vapour  of  this  compound  is  passed 
through  a  heated  tube,  it  is  transformed  into  the  isomeric 
a-pyridyl-pyrrole,  CH-CH 


This  forms  a  potassic  derivative  which  with  methyl  iodide 

CH-CH 
CH 


N.CH3 


rCH3I 
and  this,  when  distilled  with  lime,  gives 


a-pyridyl-N-methyl-pyrrol,  which  can  be  converted  into 
a-pyridyl-N-methyl-pyrrolidine  (z-nicotine)  by  the  addition 
of  hydrogen.  The  racemic  alkaloid  thus  obtained  may  be 
resolved  into  its  optically  active  components  by  the  aid  of 
d-tartaric  acid  when  J-nicotine-d-tartrate  crystallizes  out  first. 

B.  Bases  derived  from  Quinoline 

Among  tnese  are  the  alkaloids  contained  in  the  barks  of 
certain  species  of  Cinchona. 

(a)  Quinine,  C2qH2402N2  -f  3H20,  a  diacid  base  of  intensely 
bitter  taste  and  alkaline  reaction,  of  which  the  sulphate  and 
chloride  are  universally  used  as  febrifuges.  It  crystallizes 
in  prisms  or  silky  glistening  needles,  melts  at  177°  when 
anhydrous,  is  sparingly  soluble  in  water,  and  is  laevo-rotatory. 


QUINOLINE  BASES  559 

The  quinine  salts  in  dilute  solution  are  characterized  by  a 
magnificent  blue  fluorescence. 

As  a  base  quinine  is  a  tertiary  diamine,  but  it  contains  in 
addition  —  as  its  reactions  show  —  one  hydroxy-,  one  methoxy- 
group  and  an  ethylene  linking,  and  seems  to  be  built  up  of 
two  different  ring  systems,  in  accordance  with  the  following 
formula  : 

(CH30)  -  C9H5N 


The  first  of  these  represents  the  radical  of  a  6-methoxy- 
quinoline,  and  this  compound  is  obtained  when  quinine  is 
fused  with  potash.  The  second  system  probably  possesses  a 
ring  similar  to  that  of  tropine,  since  it  yields  as  decomposition 
products  sometimes  a  pyridine  derivative  (e.g.  jS-ethyl-pyridine 
on  fusion  with  alkali),  and  sometimes  benzene  derivatives 
containing  no  nitrogen  (e.g.  a  phenolic  compound,  Ci0H12OH, 
together  with  ammonia,  on  successive  treatment  with  phos- 
phorus pentachloride,  potash,  and  hydrobromic  acid). 

It  yields  quinic  acid,  6-methoxy-quinoline-4-carboxylic  acid, 
CgH5N(OCH3)C02H  (p.  547),  and  meroquinine  when  oxidized 
with  dichromate  mixture. 

Meroquinine  appears  to  be  either  (a)  3-vinylpiperidyl-acetic 
acid  (B.  .30,  1326),  or  (b)  3-vinyl-4-methylpiperidine-4-car- 
boxylic  acid  (B.  28,  1060): 


(a) 

,»n-<cr,!r:  (6) 


as  it  yields  loiponic  acid,  piperidine-3  :  4-dicarboxylic  acid,  when 
oxidized  with  permanganate. 

The  formulae  suggested  for  quinine  are  therefore  either  : 

CH2  -  CH2 


CH2  ---  CH  •  CH  :  CH2 

CH2  -  CH2 

or    N  •  C(OH)(CH2X)  .  CMe 


CH2  -  CH  .  CH 


where  X  represents  the  6-methoxy-quinoline  residue  attached 
to  the  CH2  group  in  position  4. 
Quinine  is  a  valuable  drug  in  cases  of  malaria;  numerous 


560  XL.   ALKALOIDS 

substitutes  are  now  employed,  especially  derivatives  of  quinine 
which  are  free  from  bitter  taste. 

Various  esters  are  used,  e.g.  aristoquinine  is  diquinine  car- 
bonate, euquinine  is  ethyl  quinine  carbonate,  and  saloquinine  is 
quinine  salicylate. 

(b)  Cinchonine,  C19H22ON2,  is  similar  to  quinine,  but  with- 
out the  methoxy  group  in  the  quinoline  nucleus.     It  crystal- 
lizes in  colourless  prisms,  sublimes  readily,  and  is  not  so  active 
a  febrifuge  as  quinine.     When  oxidized  with  dichromate  and 
sulphuric  acid  it  yields  cinchoninic  (quinoline- 4 -carboxylic) 
acid  and  meroquinine;   with  permanganate  it  yields  cincho- 
tenine  and  carbonic  acid.     Cinchotenine  no  longer  combines 
with  hydrogen  chloride,  and  in  the  oxidation  the  double  link- 
ing present  in  cinchonine  has  been  removed  and  a  carboxylic 
group  introduced.     When  treated  with  PC15  and  then  with 
alcoholic  potash,  cinchonine  loses  a  molecule  of  water,  yielding 
cinchene,  C19H20N2,  which  can  be  hydrolysed  by  25  per  cent 
phosphoric  acid   to  lepidine   (4-methyl-quinoline)   and  mero- 
quinine. 

(c)  Conchinine,  C2()H2402N2,  and  Cinchonidine,  C19H22ON2, 
are    probably    stereoisomeric    with    quinine    and    cinchonine 
respectively,  and  are  milder  in  their  action. 

These  are  but  a  few  of  the  numerous  alkaloids  present  in 
these  barks.  In  addition,  organic  acids  (e.g.  quinic  and  quino- 
tannic)  and  neutral  substances  are  also  present. 

C.  Bases  derived  from  /so-Quinoline 

(a)  Papaverine,  C20H2104N,  is  found  (1  %)  together  with 
narcotine,  narceine,  laudanosine,  laudanine,  and  the  morphine 
alkaloids  in  opium,  the  solid  obtained  by  drying  the  juices 
extracted  from  the  seed  vessels  of  Papaver  somniferum.  In 
addition  to  some  twenty  alkaloids,  many  of  which  are  present 
in  only  small  quantities,  opium  also  contains  fats,  resins, 
sugars,  albumins,  &c.  The  alkaloid  crystallizes  in  prisms, 
m.-pt.  147°,  and  is  optically  inactive.  It  has  hypnotic  pro- 
perties, but  not  to  the  same  extent  as  morphine.  It  is  a  ter- 
tiary base,  and  all  four  oxygen  atoms  are  present  as  methoxy 
groups,  and  when  hydrolysed  with  hydriodic  acid  the  corre- 
sponding tetrahydroxy-derivative,  papaveroline,  C16H1304N,  is 
formed.  When  oxidized  with  permanganate  it  yields  first 
papareraldine,  C20H1905N,  and  finally  dimethoxy-isoquinoline- 
carboxylic  acid  and  a-carbocinchomeronic  acid  (pyridine-1 : 2 : 3- 


/SO-QUINOLINE  BASES  561 

carboxylic  acid).  When  fused  with  potash  it  takes  up  two 
hydrogen  atoms,  and  yields  4 : 5-dimethoxy-iso-quinoline  and 
3 : 4-dimethoxy  toluene. 

From  these  and  other  reactions  G.  Goldschmudt  concluded 
that  the  base  is  Si^-dimethoxybenzyl-^'ib'-dimethoxy-iso-qidnoline: 


_OMe 
— /~     \OMe 

and  this  formula  has  been  confirmed  by  Pictet  and  Gan's  syn- 
thesis (B.  1909,  42,  2943)  by  the  following  steps:— 

1.  C6H4(OMe)2          —          C6H3(OMe)2.CO.CH3 

Veratrole  or          Friedel-  Acetoveratrone 

l:2-dimethoxybenzeue    Crafts' 

—      C6H3(OMe)2.CO.CH:N.OH 

Amyl  nitrite          Isonitrosoacetoveratrone 

—      C6H3(OMe).2 .  CO  -  CH2 .  NH2HC1 

SnCla        Amino-acetoveratrone  hydrochloride. 

2.  CHO.C6H3(OMe)OH        —        CHO.C6H3(OMe)2 

Vanillin  methylated  MethylvaniUin 

—  C6H3(OMe)2.CH(OH).CN  —  C6H3(OMe)2.CH(OPI).C02H 
HCN  hydrolysis 

—  C6H3(OH)2.CH2.C02H       — •       C6H3(OMe)2.CH2.C02H 

HI         Homoprotocatechuic  acid      methylated  Homoveratric  acid 

—  C6H3(OMe)2.CH2.COCl 

Homoveratroyl  chloride. 

3.  Amino-acetoveratrone  hydrochloride  and  homoveratroyl 
chloride  condense  in  the  presence  of  cold  potassium  hydroxide, 
yielding  (OMe)2C6H3  •  CO  -  CH2 .  NH .  CO .  CH2 .  C6H3(OMe)2 ; 
this  can  be  reduced  to  the  corresponding  secondary  alcohol 
vphich  reacts  with  dehydrating  agents,  losing  two  molecules  of 
water  and  forming  3' :4'-dimethoxybenzyl- 4: 5-dimethoxy-iso- 
quinoline,  which  is  identical  with  papaverine. 

(b)  Laudanosine,  C21H2704N,  crystallizes  in  needles,  m.-pt. 
89°,  and  is  dextro-rotatory.     It  has  been  shown  by  Pictet  and 
Athanescu  (B.  33,  2346)  to  be  an  N-methyl-tetra-hydropapa- 
verine,  and   has   been  synthesised   by  Pictet  and   Finkektein 
(C.  E.  1909,  148,  295). 

(c)  Narcotine,  C22H2307N,   occurs  in  opium  (6  per  cent), 
crystallizes   in  colourless   needles,  m.-pt.   176°,  and  is  Isevo- 
rotatory.     It  is  a  feeble  tertiary  base,  and  its  salts  are  readily 
hydrolysed  by  water.     It  contains  three  methoxy  groups,  and 

(B480)     "  2N 


562  XL.   ALKALOIDS 

when  hydrolysed  by  dilute  acids  or  alkalis,  yields  opianic  acid 
and  hydro-cotarnine.  When  reduced  it  yields  meconine  and 
hydro-cotarnine,  and  when  oxidized  yields  opianic  acid  and 
cotarnirie,  and  when  heated  with  alkalis  at  220°  yields  methyl- 
amines,  thus  indicating  that  the  N-atom  is  methylated. 

The  racemic  compound  has  been  synthesised  in  small  quan- 
tities (PerUn  and  Robinson,  J.  C.  S.  1911,  776)  by  boiling  an 
alcoholic  solution  of  cotarnine  and  meconine,  and  has  been 
resolved  by  means  of  d-bromo-camphor-sul  phonic  acid. 

CH5 


Narcotine, 


OMe 
OMe 

Both  opianic  (2 : 3-dimethoxy-6-aldehydo-benzoic  acid)  acid 
and  cotarnine  have  been  synthesised.  "  The  former  by  Fritsch 
(A.  301,  351)  and  the  latter  by  Salway  (J.  C.  S.  1910,  1208): 
The  structural  formula: 


was  deduced  by  Eoser  for  cotarnine  by  a  study  of  its  degrada- 
tion products.  When  methylated  and  decomposed  by  alkalis 
it  yields  an  aldehyde,  cotarnone,  which  on  further  oxidation 
gives  a  methoxy-dibasic  acid,  known  as  cotarnic  acid,  and  this 
with  hydriodic  acid  and  phosphorus  at  160°  yields  gallic  acid 
(3:4:5-trihydroxybenzoic  acid).  Although  cotarnine  itself  is 
not  an  iso-quinoline  derivative,  its  salts  are.  The  salt  forma- 
tion is  accompanied  by  a  closing  of  the  ring  (cf.  Debbie,  Lauder, 
and  Tinkler,  J.  C.  S.  1903,  598): 


/SO-QUINOLINE  BASES  563 

Hydro-cotarnine  is  also  a  reduced  iso-quinoline  derivative : 


The  steps  in  the  synthesis  of  cotarnine  are :  Myristic  aldehyde 
(3-methoxy-4:5-methylenedioxy-benzaldehyde)  — ••  3-methoxy- 

Perkin's  synthesis. 

4 : 5-methylenedioxy-cinnamic  acid  — >  corresponding  dihydro 

red. 

acid  — »•  acid   amide  — »•  /3- 3 -methoxy -4  :  5-methylenedioxy- 

—  co. 

phenylethylamine  — *•  phenacetyl-derivative  of  amine  — *•  8-me- 
thoxy-6  :  7-methylenedioxy-l-benzyl-3  :  4 -dihydro -iso-quino- 
line — -  1-benzylhydrocotarnine  — *•  cotarnine. 

Methochloride  H2S04 

with  tin  and  HC1.  +Mn02.  e 

(d)  Hydrastine,  C21H2106N,  occurs  in  the  roots  of  Hydrastis 
canadensis,  and  differs  from  narcotine  by  having  no  methoxy 
group  in   the   iso-quinoline  ring.     When  oxidized   it  yields 
opianic  acid  and  hydrastinine,  which  is  the  analogue  of  cotar- 
nine.    (Synthesis,  cf.  Freund,  B.  20,  2403.) 

(e)  Berberine,  C20Hllr04N,  H20,  is  the  chief  alkaloid  present 
in  Hydrastis,  but  has  not  marked  physiological  properties.    The 
probable  structural  formula  is  I.  (Perkin  and  Robinson,  J.  C.  S. 
1910,  305): 

CH2 


I.  CH 


(/)  Corydaline,  C22H2704N,  from  Corydalis  cava,  crystallizes 
in  prisms,  m.-pt.  134'5  ,  and  contains  four  methoxy  groups. 
The  structural  formula  suggested  by  DdbUe  and  Lander  ( J.  C.  S. 
1903,  605)  is  II: 

CH2 


/YXc 

ii.  1 1  • 

OMeL     IL,  N— CHMe 

<T        \__OMe 

[2 /       V)Me. 

\.       / 


564  XL.   ALKALOIDS 

D.  The  Morphine  Group  of  Bases 

The  three  alkaloids  morphine,  codeine,  and  thebaine  are 
characterized  by  containing  a  phenanthrene  nucleus  in  addi- 
tion to  a  nitrogen  ring.  They  are  all  present  in  opium. 

(a)  Morphine,  C17H1903N,  constitutes  on  the  average  10  per 
cent  of  opium.  It  crystallizes  in  small  prisms  (+H20),  melt- 
ing and  decomposing  at  230°,  has  a  bitter  taste,  and  is  a  valu- 
able soporific.  It  is  a  mono-acid  tertiary  base,  containing  two 
hydroxyl  groups,  one  of  which  is  phenolic  and  the  second  alco- 
holic. When  distilled  with  zinc  dust  it  yields  phenanthrene 
together  with  pyrrole,  pyridine,  and  trimethylamine.  Further 
proof  of  the  presence  of  the  phenanthrene  nucleus  has  been 
afforded  by  the  process  of  exhaustive  methylation.  With 
methyl  iodide  it  yields  codeine  methiodide,  formed  by  the 
methylation  of  the  phenolic  hydroxyl  group  and  addition  of 
methyl  iodide  to  the  tertiary  N-atom.  This  product,  with 
potassium  hydroxide,  loses  hydrogen  iodide  and  yields  a 
tertiary  base,  methylmorphimethine,  which  with  acetic  anhydride 
gives  3-methoxy-4-hydroxy-phenanthrene  (methylmorphol)  and 
hydroxyethyldimethylamine,  OH.CH2-CH2.NMe2.  The  for- 
mula  suggested  by  Pschorr  is : 

CH,  NCH3 


(b)  Codeine,  C18H2103N,  is  a  methyl  derivative  of  morphine, 
and  can  be  obtained  from  the  latter  by  methylation  of  its 
phenolic  group.    When  oxidized  it  yields  the  ketone  codeinone, 
and  this  with  acetic  anhydride  yields  hydroxyethyl-methyl- 
amine  and  3-methoxy-4 : 6-dihydroxy-phenanthrene. 

(c)  Thebaine  is  morphine  in  which  both  phenolic  and  alco- 
holic hydroxyls  are  methylated. 

Numerous  alkyl  derivatives  of  morphine  are  manufactured 
and  used  as  drugs  in  place  of  codeine.  Dionine  is  ethyl- 
morphine  hydrochloride,  peronine  is  benzylmorphine  hydro- 
chloride,  heroin  is  diacetylmorphine. 

For  synthetical  products  allied  to  morphine  see  Knorr,  A« 
301,  1;  307,  171,  187;  B.  32,  732. 


STRYCHNINE,  SOLANINE,  AND  COCA  BASES     565 

E.  Strychnine  Bases 

Strychnos  nitx  vomica  and  certain  other  beans  contain : 

(a)  Strychnine,  C21H2202N2.     This  is  excessively  poisonous, 
produces   tetanic   spasms,   crystallizes  in  four-sided   prisms, 
and  yields  quinoline   and  indole   when   fused   with  potash, 
/3-picoline    when    distilled    with    lime,    and    carbazole    when 
heated  with  zinc  dust.     It  is  a  mono-acid  tertiary  base,  and 
melts  at  284°.     (For  suggested  formula  see  Perkin  and  Robin- 
son, J.  C.  S.  1910,  305.) 

(b)  Brucine,  C23H2604N2,  4H20,  which  crystallizes  in  prisms, 
and  is  converted  into  homologues  of  pyridine  on  fusion  with 
potash. 

F.  Solanine  and  Coca  Bases 

Atropine  and  hyoscyamine  are  isomeric  bases  of  the  for- 
mula C17H2303N,  which  can  be  respectively  prepared  from 
Atropa  Belladonna  (Deadly  Nightshade)  and  Datura  Stramonium, 
and  which  are  remarkable  for  their  mydriatic  action  (power 
of  dilating  the  pupil  of  the  eye). 

Atropine  crystallizes  in  colourless  prisms  or  needles  melting 
at  115°,  possesses  an  extremely  bitter  taste,  is  optically  in- 
active, and  is  hydrolysed  by  baryta  water  to  (//-tropic  acid 


tropine.     The  alkaloid  can  be  synthesised  by  evaporating 
dilute  hydrochloric  acid  solution  of  tropine  and  tropic  acid. 
A  complete  synthesis  of  atropine  has  been  accomplished,  as 
both  tropic  acid  and  tropine  have  been  synthesised. 

When  optically  active  (d-  and  I)  tropic  acids  are  used,  a 
dextro-  and  a  laevo-rotatory  atropine  result  (B.  22,  2590). 
And  if,  instead  of  tropic  acid  itself,  other  organic  acids  are 
employed,  homologous  bases,  the  "tropeines",  are  obtained; 
thus  mandelic  acid  yields  homatropine,  C16H21N08,  which  exerts 
like  atropine  a  mydriatic  action,  although  a  less  lasting  one 
(Ladenburg,  A.  217,  82;  Jowett  and  Pyman,  J.  C.  S.  1909,  1090). 

Tropine  itself  is  a  cycloheptanol  with  a  nitrogen  bridge : 

CH2-CH — CH2 

NCH3  CH-OH 
CH2.CH — CH2 

(fTiUsWter,  B.  1898,  31,  1538,  2498,  2655).     For  synthesis 
cf.  Willslatter,  A.  1901,  317,  307. 


566  XL.    ALKALOIDS 

It  is  a  tertiary  base,  crystallizes  in  plates,  m.-pt.  62°,  and 
b.-pt.  220°. 

On  oxidation  it  yields  the  ketone  tropinone,  and  then  tro- 
pinic  acid,  or  N-methyl-pyrrolidine-a-carboxylic-a! '-acetic  acid. 
Concentrated  hydrochloric  acid  converts  it  into  tropidine, 

CHjj-CH — CH2 
NCH3  CH 
CH2-CH — CH2 

an  oily  base  distilling  at  162°,  and  also  obtainable  by  the 
elimination  of  carbon  dioxide  from  anhydro-ecgonine. 
Ecgonine,  or  tropine-carboxylic  add, 

CHjs-CH — CH-CO2H 

NCHS  CH-OH 
CH2.CH — OK, 

crystallizes  with  one  molecule  of  water,  and  may  be  obtained 
by  the  hydrolysis  of  products  contained  in  coca  leaves.  It 
melts  at  198°,  and  is  laevo-rotatory;  and  on  warming  with 
alkalis,  gives  iso-ecgonine,  which  is  dextro-rotatory.  As  an 
alcohol  it  forms  a  benzoyl  derivative,  and  as  an  acid  a  methyl 
ester.  (See  Cocaine.) 

Cocaine,  or  benzoyl-l-ecgonine  methyl  ester, 

CH2-CH CH.C02CHS 

NCH3  CH.O-COC6H6 
CH2-CH — CH2 

is  the  active  constituent  of  the  coca  leaf  (Erythroxylon  coca);  it 
melts  at  98°,  is  Isevo-rotatory,  and  is  used  in  surgery  for  deaden- 
ing pain.  It  has  been  synthesised  by  the  action  of  benzoic  an- 
hydride and  methyl  iodide  on  ecgonine  (B.  1885,  18,  2953). 

Hyoscyamine,  which  crystallizes  in  needles  or  plates,  melt- 
ing at  109°,  resembles  atropine  closely,  and  is  readily  trans- 
formed into  the  latter  under  the  influence  of  various  alkalis 
(Will,  B.  21,  1725,  2777).  In  contact  with  water  it  is  slowly 
hydrolysed  to  /-tropic  acid  and  inactive  tropine.  Atropine  is 
racemic  hyoscyamine. 

Various  substitutes  for  cocaine  have  been  recommended,  as 
its  solutions  do  not  keep  well.  Willstatter  (B.  29,  1575,  2216) 
obtained  an  isomeride  of  ecgonine  by  the  addition  of  HCN  to 
tropinone  (p.  566)  and  subsequent  hydrolysis,  and  from  this 


ETHEREAL  OILS  567 

a  -cocaine  was  obtained  by  benzoylation  and  esterification. 
a-Cocaine  contains  both  C02Me  and  COPh  groups  attached  to 
the  same  carbon  atom.  a-Eucaine  is  a  cheap  substitute  for 

cocaine  prepared  from  triacetonamine,  NH<^QJ^2[Qg2^>CO 

(p.  134),  by  addition  of  HCN,  hydrolysis,  benzoylation  of  the 
hydroxy-acid  thus  formed,  and  final  methylation  of  the  imino 
and  carboxylic  groups.  Its  structure  is: 


/3-Eucaine  has  the  formula: 

.;;:  :  NH< 

(Harries,  B.  29,  2730). 


XLI.  TEEPENES  AND  CAMPHORS 

For  history  of  terpenes  see  Tilden,  Science  Progress,  1911, 
6,  46.  Cf.  Wallaces  "Terpene  und  Camphor",  1909. 

Ethereal  Oils. — Many  plants,  especially  varieties  of  Coniferse 
and  of  Citrus,  contain,  in  their  blossoms  and  fruits,  oily  sub- 
stances to  which  they  owe  their  peculiar  fragrance  or  odour, 
and  which  can  be  obtained  from  them  by  distillation  in  steam 
or  by  pressure.  These  oils,  "ethereal  oils",  were  formerly 
grouped  together  in  a  special  class,  but  now  they  are  recog- 
nized as  being  more  or  less  heterogeneous;  thus  oil  of  bitter 
almonds  is  benzoic  aldehyde,  and  Roman  oil  of  cumin  is  a 
mixture  of  cymene  and  cumic  aldehyde,  &c.  Many  of  these 
ethereal  oils  contain  unsaturated  hydrocarbons,  which  are  usu- 
ally termed  terpenes.  The  common  hydrocarbons  met  with 
have  the  general  formula  C10H16,  and  are  spoken  of  as  terpenes 
proper;  but,  in  addition  to  these,  hydrocarbons,  represented 
by  the  formula  C5H8  and  known  as  hemiterpenes,  exist.  The 
commonest  of  these  is  isoprene,  obtained  by  distilling  caout- 
chouc. Hydrocarbons  represented  by  the  formula  C15H24  are 
termed  sesquiterpenes,  and  the  more  complex  hydrocarbons, 
(C5Ho)n,  polyterpenes.  Certain  ethereal  oils  consist  chiefly  of 
such  hydrocarbons,  e.g.  turpentine,  oil  of  citron,  orange  oil,  and 
oil  of  thyme.  Other  oils  contain  appreciable  amounts  of  oxy- 
genated compounds,  mainly  of  an  alcoholic  or  ketonic  character, 


668  XLI.   TERPENES  AND  CAMPHORS 

e.g.  camphor  and  menthone,  C10H160,  pulegone,  &c.  Many  of 
these  terpenes  and  ketones  are  reduced  benzene  derivatives, 
e.g.  limonene,  menthone;  others  again  are  more  complex  ring 
compounds,  e.g.  pinene  and  camphor.  In  addition  to  these 
two  groups  of  compounds  a  third  group  has  been  discovered 
within  recent  years,  namely,  open-chain  olefinic  alcohols,  alde- 
hydes, or  ketones,  e.g.  citronellal,  geraniol,  linalool. 

The  terpenes  are  widely  distributed  in  the  vegetable  king- 
dom, especially  in  the  Coniferse  (Pinus,  Picea,  AUes,  &c.),  in 
the  varieties  of  Citrus,  &c.  The  products  which  are  isolated 
in  the  first  instance  from  the  individual  plants,  and  which 
according  to  their  source  are  designated  terpene,  citrene  (from 
oil  of  citron),  hesperidene  (from  oil  of  orange),  thymene  (from 
thyme,  carvene  (from  oil  of  cumin),  eucalyptene,  olibene,  &c., 
have  for  the  most  part  the  formula  C10H16,  and  approximately 
jqual  boiling-points  (160°- 190°);  they  are  not,  however, 
chemical  individuals,  but  mixtures  of  isomeric  compounds. 

With  the  exception  of  camphene  they  are  all  liquid,  but  it 
is  hardly  possible  to  separate  them  completely  by  fractional 
distillation  (see  table,  p.  578,  for  boiling-points).  The  terpenes 
can,  however,  be  obtained  chemically  pure  from  crystalline 
derivatives.  Quite  recently,  numerous  compounds  belonging 
to  this  class  have  been  synthesised. 

For  simplicity  the  terpenes  and  allied  oxygen  compounds 
(camphors)  may  be  divided  into  the  following  groups: — 

A.  Open-chain  olefinic  compounds. 

B.  Monocyclic   terpenes   (mainly  reduced   benzene  deriva- 
tives). 

C.  Complex  cyclic  terpenes. 

Practically  all  the  compounds  dealt  with  in  these  three 
divisions  could  have  been  discussed  under  the  aliphatic  and 
cyclic  compounds.  A  clearer  view,  however,  of  their  relation- 
ships is  obtained  by  bringing  them  together  under  the  general 
heading  of  terpenes  and  camphors. 

A.  Open-chain  Olefinic  Terpenes  and  Camphors 

Isoprene,  the  best-known  hemiterpene,  is  a  diolefine  repre- 
sented by  the  constitutional  formula,  CH2 :  CMe  •  CH :  CH2, 
2-methyl-A1:3-butadiene.  It  is  a  colourless  liquid,  b.-pt.  37°, 
is  formed  by  the  dry  distillation  of  rubber,  or  by  decompos- 
ing turpentine  at  a  dull  red  heat  (cf.  Staudinger,  B.  44,  2212). 
At  300°  it  undergoes  polymerization  to  diisoprene  (probably 


CITRONELLAL  569 

dipentene),  and  is  transformed  into  products  analogous  to 
rubber  when  treated  with  concentrated  hydrochloric  acid, 
when  kept  for  some  time  or  when  exposed  to  sunlight  in 
fche  presence  of  traces  of  acid.  Two  syntheses  of  isoprene 
are  of  interest. 

(a)  From    methyl -pyrrolidine  by   exhaustive    methylation 
(Euler,  J.  pr.  [ii],  57,  132): 

CH2— CH2,      H      _      ^" 

CHMe  •  CH2^  methylated  CHMe 

—    CH2:CH.CHMe.CH2.NMe2 

—      CH2 :  CH  •  CHMe  •  CH2  •  NMe3I 
methylated      __    CH2:CH.CMe:CH2  +  NMe3  +  HL 

KOH 

(b)  From  dimethyl-allene  by  the  addition  of  two  molecules 
of  hydrogen  bromide  and  subsequent  elimination  of  the  same 
(Ipatieff,  ibid.  55,  4): 

CMe2:C:CH2  —  CMe2Br.CH2.CH2Br  —  CH2:CMe.CH:CH2. 

It  has  been  suggested  that  indiarubber  should  be  syntb.esised 
from  isoprene,  but  the  cost  of  the  isoprene  has  so  far  interfered 
with  the  adoption  of  this  method  on  the  commercial  scale. 

Practically  all  the  natural  products  belonging  to  this  group 
contain  oxygen  and  are  either  aldehydes  or  alcohols. 

Citronellal,  CH2 :  CMe .  CH2 .  CH2 .  CH2  -  CHMe  -  CH2  •  CHO, 
is  an  example  of  an  olefine  aldehyde;  it  is  present  in  citronella 
oil  and  also  in  lemon-grass  oil,  together  with  citral  and  geraniol. 
It  has  b.-pt.  205°-208°.  Its  aldehydic  nature  is  proved  by  the 
readiness  with  which  it  is  reduced  to  a  primary  alcohol,  citron- 
ellol,  and  oxidized  to  a  monobasic  acid,  citronellic  acid,  con- 
taining the  same  number  of  carbon  atoms.  By  oxidizing  its 
dimethyl-acetal,  Harries  and  SchauwecJcer  (B.  34,  1498,  2981) 
obtained  a  dihydroxy-derivative,  thus  proving  the  presence 
of  an  olefine  linking;  and  on  farther  oxidation  with  chromic 
anhydride  they  obtained  the  acetal  of  a  keto-aldehyde  contain- 
ing nine  carbon  atoms,  thus  proving  that  the  double  bond  is 
between  the  last  and  last  but  one  carbon  atoms  with  respect 
to  the  aldehyde  group: 

CH2:CMe(CH2)3.CHMe.CH2.CHO  -f  4O 

=  OO2  -f-  H2O  +  O:CMe(CH2)3.CHMe.CH2.CHO. 

The  positions  of  the  methyl  groups  are  proved  by  the  rela- 


670  XLI.   TERPENES  AND  CAMPHORS 

tionship  of  the  aldehyde  to  isopulegol,  into  which  it  is  trans- 
formed when  kept  for  some  time,  or  more  quickly  when  heated 
with  acetic  anhydride  at  180°: 


The  constitution  of  pulegol  follows  from  the  fact  that  when 
oxidized  it  yields  isopulegone,  and  this  with  baryta  is  trans- 
formed into  pulegone  by  the  wandering  of  an  olefine  linking. 


Pulegone 

An  interesting  reaction  of  citronellal  is  its  oxidation  in 
alkaline  solution  with  permanganate,  when  it  yields  acetone 
and  /?-methyladipic  acid,  a  result  which  would  lead  to  the  con- 
clusion that  the  double  bond  is  in  position  5:6  with  respect 
to  the  CHO  group. 

The  only  manner  of  reconciling  this  reaction  with  the 
reactions  already  given  is  the  assumption  that  in  the  oxida- 
tion in  alkaline  solution  a  wandering  of  the  double  bond 
occurs  : 

CH2  :  CMe  •  (CH2)3  •  CHMe  •  CH2  •  CHO 

—  CMe2:CH(CH2)2.  CHMe  -CH2.  CHO. 

Citral  or  geranial,  C10H160,  occurs  in  both  oil  of  lemons 
and  of  oranges,  and  may  also  be  obtained  by  the  oxidation  of 
geraniol.  Lemon-grass  oil  contains  70-80  per  cent.  It  is  a 
colourless  oil,  and  distils  at  110°-112°  under  12  mm.  pressure. 
Its  constitution  is  represented  as: 

CMe2  :  CH  •  CH2  •  CH2  •  CMe  :  CH  •  CHO. 

Its  aldehydic  nature  follows  from  its  reduction  to  geraniol, 
and  its  oxidation  to  an  acid  containing  the  same  number  of 
carbon  atoms,  namely,  geranic  acid.  Its  unsaturated  character 
and  the  positions  of  the  double  bonds  within  the  molecule 
follow  from  its  general  properties,  but  more  especially  (a)  from 
its  products  of  oxidation,  viz.  acetone,  laevulic  acid,  and  carbon 
dioxide  : 

CMe2:  !  CH.CH2.CH2-CMe:  j  CH-CHO 

—  MejjCO  +  CO2H-CH2.CHa.COMe  -f  20Oa; 


GERANIOL  671 

(b)  from  its  conversion  into  methyl-heptenone  and  acetalde- 
hyde  by  means  of  potassium  carbonate: 

CMe2:CH.GH2.CH2.CMe:CH.CHO=CMe2:CH.CH2.CH2.COMe 
+     0  H2  +CH3.CHO. 

When  heated  with  potassium  hydrogen  sulphate,  citral  is  con- 
verted into  ^Mjymene. 

Both  citral  and  geranic  acid  have  been  synthesised  by 
Earlier  and  Bouveault  (C.E.  1896,  122,  393).  1-Methyl-A'- 
heptenone  reacts  with  metallic  zinc  and  iodo -acetic  acid 
(Reformatsky  reaction),  yielding  the  compound: 

H2.COaH 


Ls 
With  dilute  acid  this  yields  the  hydroxy-acid: 

CMe2 :  CH  •  CH2  •  CH2  •  CMe(OH)  •  CHj  •  CO2H, 


and  when  this  is  distilled  with  acetic  anhydride,  water  is 
eliminated  and  geranic  acid  formed. 

Geranic  acid,  when  reduced  in  the  form  of  its  ethyl  ester 
with  sodium  and  amyl  alcohol,  yields  i-rhodinic  acid: 

CMe2 :  CH  •  CH,  •  CH2  -  CHMe  •  CH2  •  C02H, 

which  is  structurally  isomeric  with  citronellic  acid;  and  when 
ethyl  rhodinate  is  reduced  with  sodium  and  alcohol,  the  corre- 
sponding primary  alcohol,  rhodinol,  is  formed. 

Citral  occurs  in  two  stereoisomeric  forms,  termed  a-  and 
6-citrals.  They  are  both  inactive,  and  the  isomerism  is  of  the 
same  type  as  that  met  with  in  the  crotonic  acids  and  fumaric 
and  maleic  acids  (p.  243). 

Geraniol,  C10H180,  is  the  alcohol  corresponding  with  citral, 
and  is  the  chief  constituent  (90  per  cent)  of  Indian  geranium 
oil,  which  is  largely  used  for  adulterating  rose  oil.  Its  con- 
stitution follows  from  its  relationship  to  citral  and  geranic 
acid,  into  which  it  is  readily  oxidized. 

By  reducing  citral  with  alcohol  and  sodium  amalgam,  two 
stereoisomeric  alcohols,  geraniol  and  nerol,  are  obtained,  and 
both  yield  citral  when  reoxidized.  Both  alcohols  yield  ter- 
pineol  by  the  action  of  acetic  acid  containing  1  to  2  per  cent 
of  sulphuric  acid,  but  nerol  reacts  about  nine  times  as  readily 
as  geraniol.  The  formation  of  terpineol  can  be  accounted  for 
by  the  addition  and  withdrawal  of  water.  The  two  alcohols 


572  XLI.   TERPENES  AND  CAMPHORS 

are  structurally  identical,  and  are  represented  by  the  two 
stereochemical  formulae : 


H.C.CH2.OH  01 

I.  1|  IL 

CMe2:CH.(CH2)2-C.CH3  CMe2:CH.(CH2).C.CH3 

Geraniol  Nerol. 

as  No.  II  would  lose  water  more  readily  than  No.  I  to  form 
a  six-membered  ring.  It  is  probable  that  citral  a  corresponds 
with  geraniol,  and  citral  I  with  nerol. 

Linalool  or  coriandrol  is  isomeric  with  geraniol,  into  which 
it  is  readily  transformed  by  the  action  of  dilute  organic  acids. 
It  occurs  as  linalyl  acetate  in  lavender,  sage,  and  coriander 
oils.  It  is  optically  active,  reacts  as  a  tertiary  alcohol,  and 
hence  is  structurally-  and  not  stereo-isomeric  with  geraniol. 
Its  reactions  agree  best  with  the  formula: 

CMe2 :  CH  •  CH2 .  CH2  •  CMe(OH)  •  CH :  CH^ 

and  its  conversion  into  geraniol  probably  depends  upon  the 
addition  and  subsequent  removal  of  water,  the  glycol, 

CMe2:CH.CH2.CH2.CMe(OH).CH8.CH2.OH, 

being  formed  as  the  intermediate  product.     /-Linalool  reacts 
with  acetic  anhydride,  yielding  nerol,  geraniol,  and  d-terpineol. 
Compounds  of  this  type  with  the  carbon  system : 

7654321 


are  readily  transformed  into  derivatives  of  j9-cymene  by  union 
between  carbon  atoms  numbers  1  and  6  (cf.  p.  571),  or  into 
tetrahydrobenzene  derivatives  by  union  of  numbers  2  and  7 
(cf.  lonone,  p.  589;  also  conversion  of  citral  into  a-  and 
/?-cyclo-citrals,  cyclic  /?y  and  a/3  unsaturated  aldehydes). 

B.  Monoeyelie  Terpenes  and  Camphors 

I.  Terpenes. — These  compounds  are  to  be  regarded  as  hydro- 
derivatives  of  cymene  (p.  352).  Their  close  relationship  to 
cymene  can  be  shown  in  very  different  ways:  e.g.  (a)  the 
hydrocarbon  terpinene  when  heated  with  iodine  is  transformed 
into  ^-cymene,  i.e.  ^-methyl-isopropyl  benzene;  (b)  the  ketonc 


MONOCYCLIC  TERPENES  573 

carvone  when  heated  with  mineral  acids  yields  carvacrol,  i.e. 
l-methyl-2-hydroxy-4-isopropyl  benzene  (p.  417);  (c)  on  oxi- 
dation many  terpenes  yield  terephthalic  acid;  (d)  when  bro- 
minated  and  then  reduced  many  monocyclic  terpenes  yield 
benzene  hydrocarbons  (B.  1898,  31,  2068). 

The  unsaturated  nature  of  these  compounds  follows  from 
the  readiness  with  which  they  form  additive  compounds;  they 
yield  dihydrochlorides,  C^H^Cl^  tetrabromides,  C^H^Br^ 
nitroso-chlorides,  C10H]6(NOC1)2,  nitrosites,  C10H16(NO)(N02), 
and  nitrosates,  C10H16N204.  These  compounds  are  of  con- 
siderable importance,  as  most  of  them  are  well-defined  crystal- 
line compounds  with  definite  melting-points,  and  can  therefore 
be  made  use  of  in  separating  and  identifying  the  various 
liquid  terpenes.  The  nitroso-chlorides  were  first  prepared  by 
Tilden  (J.  C.  S.  1877,  554),  by  the  direct  action  of  nitrosyl 
chloride,  but  are  now  usually  obtained  by  Wallaces  method, 
viz.  by  the  action  of  a  mixture  of  ethyl  nitrite,  acetic  and 
hydrochloric  acids  on  the  hydrocarbon.  The  nitrosites  are 
usually  obtained  by  the  action  of  sodium  nitrite  and  acetic 
acid  on  the  hydrocarbon,  and  the  nitrosates  by  the  direct 
addition  of  nitric  peroxide  or  by  the  action  of  amyl  nitrite 
and  concentrated  nitric  acid. 

An  interesting  group  of  compounds  are  the  nitrolamines, 
obtained  by  the  action  of  amines  (piperidine  or  benzylamine) 
on  the  nitroso-chlorides.  They  contain  the  NHE-group  ID 
place  of  the  chlorine  of  the  nitroso-chlorides.  Such  com- 
pounds crystallize  well,  and  can  be  used  for  identifying  the 
various  terpenes. 

All  these  reactions  point  to  the  presence  (a)  of  a  six- 
membered  carbon  ring  in  the  monocyclic  terpenes;  (b)  to  the 
presence  of  two  side  chains,  usually  in  ^-positions,  one  consist- 
ing of  the  CHg-group,  and  the  second  containing  the  grouping 

— CX^o;  (c)  to  the  presence  of  two  double  bonds  in  the  mole- 
cule. These  may  be  both  in  the  carbon  ring,  or  one  in  the 
ring  and  one  in  a  side  chain,  e.g.: 

CH3 

H/V 


II 

qcH8)a 


574  XLI.   TERPENES   AND  CAMPHORS 

Fourteen  such  isomerides  are  theoretically  possible.     The 
carbon  atoms  are  usually  numbered  as  follows: 


The  saturated  compound  C10H20,  viz.  p -methyl -isopropyl- 
hexamethylene,  is  called  terpane*,  and  the  compounds  C10H16 
are  terpadienes.  I  is  A-l :  4-terpadiene,  II  is  A-l :  4  (8)-ter- 
padiene,  and  III  A-l :  8  (9)-terpadiene. 

The  double  linking  in  No.  II  between  a  carbon  atom  in  the 
ring  and  a  carbon  of  a  side  chain  is  termed  a  semicyclic  linking. 
Such  an  unsaturated  linking  is  quite  stable  under  the  influ- 
ence of  heat,  but  in  the  presence  of  acids  it  wanders  into 
the  nucleus,  e.g.  A4(8)  ^-menthene  is  readily  transformed  into 
A3  j9-menthene. 

A  few  of  the  terpenes  contain  the  methyl-  and  isopropyl- 
groups  in  the  meta  positions,  e.g.  sylvestrene;  such  com- 
pounds are  termed  m-terpadienes. 

The  nitroso-chlorides  are  frequently  colourless,  and  then  ap- 
pear to  be  bimolecular;  some  give  blue  solutions  containing  the 
monomolecular  form.  Compounds  with  a  semicyclic  linking 
^>C:CR2  yield  unimolecular  blue  nitroso-chlorides  volatile 
with  steam.  The  blue  compounds  are  true  nitroso-compounds. 
When  the  NO-group  becomes  attached  to  ^>CH  it  usually 
passes  over  into  the  isonitro-group  ^>C:N»OH,  and  the  com- 
pound becomes  colourless. 

The  following  hydrocarbons  belong  to  this  group : — 

Dipentene,  A-l: 8  (9)-terpadiene  or  inactive  limonene  (see 
formula  III;  for  constitution  cf.  B.  1895,  28,  2145;  1898,  31, 
1402;  1900,  33,  1457).  It  occurs  together  with  cineol  in  Oleum 
tince,  and  is  prepared  by  heating  pinene,  camphene,  sylvestrene, 
or  limonene  to  250°-270°  for  several  hours,  and  also  by  the 
abstraction  of  hydrogen  chloride  from  its  dihydrochloride.  It 
is  further  produced  from  pinene  under  the  influence  of  dilute 
alcoholic  sulphuric  acid,  from  terpin  hydrate  and  terpineol  by 
the  elimination  of  water,  by  the  polymerization  of  isoprene, 
and,  together  with  the  latter  substance,  on  distilling  caout- 
chouc. Its  formation  from  isoprene,  CH2 :  C(CH8)  •  CH :  CH2,  by 
heating  at  300°  is  a  synthesis,  since  isoprene  has  been  synthe- 
sised  (p.  569).  It  is  a  liquid  of  pleasant  odour  like  that  of  oil 

*  The  name  menthane  is  sometimes  used  for  this  hydrocarbon  and 
menthadienea  for  the  terpadienes. 


LIMONENES  575 

of  citron,  boils  at  175°-176°,  and  is  more  stable  than  pinene, 
although  it  can  still  be  transformed  into  terpinene  by  acids. 
It  readily  forms  dipentene  dihydrochloride  with  hydrochloric 
acid,  and  with  bromine  a  crystalline  tetrabromide  melting  at 
125°.  Its  (inactive)  nitroso-chloride  yields,  by  the  elimination 
of  hydrogen  chloride,  the  so-called  nitroso-dipentene  (inactive 
carvoxime),  melting  at  93°. 

c?-Limonene,  hesperidene,  dtrene,  or  carvene.  The  oil  of  the 
orange  rind  consists  almost  entirely  of  dextro-limonene,  which 
is  also  the  chief  constituent  of  carvene,  oil  of  dill,  oil  of  eri- 
geron,  &c.;  oil  of  citron  consists  mainly  of  d-limonene  and 
pinene.  It  boils  at  175°,  and  forms  a  dextro-rotatory  tetra- 
bromide,  C10H16Br4,  which  melts  at  104°.  The  dextro-  and 
laBvo-tetrabromides  are  identical,  except  that  their  crystals  are 
the  mirror  images  of  one  another.  Dextro-limonene  is  very 
readily  racemized  to  dipentene. 

/-Lunonene  is  present  together  with  Isevo-pinene  in  the  oil 
of  fir  cones. 

I-  and  d-limonenes  yield  nitroso-chlorides,  C^H^NOCl,  of 
corresponding  rotatory  powers;  and,  on  the  elimination  of 
hydrogen  chloride  from  these,  /-  and  J-nitroso-limonenes, 
C10H15NO,  which  are  identical  with  the  carvoximes. 

The  conversion  of  geraniol  into  dipentene  is  of  considerable 
interest  (Tiemann  and  Schmidt,  B.  1895,  28,  2137): 

(CH3)2C:CH.CH2.CH2.qCH3):CH.CH2OH 

Geraniol 

-*     (CH3)8C(OH).CH2.CH2.CH2.C(CH3XOH).CH2.CH2OH 
+  2H2O  Terpin  hydrate 


Terpto 


-2H»°  *p*2UT 

Dipentene  readily  combines  with  hydrogen  chloride, 
a  dihydrochloride,  C]0H18C12,  which  melts  at  50°.  The  same 
compound  is  also  formed  by  the  action  of  hydrogen  chloride  on 
limonene  or  on  pinene,  and  when  left  in  contact  with  aqueous 
alcohol  yields  terpin  hydrate,  C10H19(OH)3  (cf.  formula  above), 
in  the  form  of  large  rhombic  crystals  melting  at  117°. 

Terpinene,  probably  &-l:3-terpadienet  is  one  of  the  most 
stable  of  the  terpenes.  It  may  be  obtained  by  the  action  of 
alcoholic  sulphuric  acid  on  dipentene,  or  on  other  compounds 


576  XLI.   TERPENES  AND  CAMPHORS 

which  yield  dipentene  as  an  intermediate  product,  e.g.  by 
shaking  pinene  with  concentrated  sulphuric  acid,  or  by  boiling 
terpin  hydrate  with  dilute  sulphuric  acid.  It  boils  at  179°- 
181°,  is  optically  inactive,  and  most  of  its  derivatives  are  oils, 
with  the  exception  of  the  nitrosite,  which  melts  at  155°. 

Terpinolene,  A-l:4  (8)-terpadiene,  is  formed  when  terpineol 
is  boiled  for  a  short  time  with  oxalic  acid  solution.  It  boils 
at  183°-185°,  and  is  readily  transformed  by  acids  into  ter- 
pinene.  It  forms  a  blue  nitroso-chloride. 

Sylvestrene,  Carvestrene,  A-l:8  (9)-mrterpadiene,  b.-pt.  175°, 
is  the  chief  dextro-rotatory  constituent  of  Swedish  and  Eussian 
oil  of  turpentine.  It  is  one  of  the  most  stable  of  the  terpenes, 
and  gives  a  magnificent  blue  coloration  with  acetic  anhydride 
and  concentrated  sulphuric  acid.  The  CH3  and  C3H5  substi- 
tuents  are  in  the  m-positions,  as  treatment  with  bromine  con- 
verts it  into  T/Zrcymene. 

It  has  been  synthesised  from  m-hydroxybenzoic  acid  by 
Perkin  and  Tattersall  (J.  C.  S.  1907,  480)  by  reducing  to  its 
hexahydro  derivative,  oxidizing  to  y-ketohexahydrobenzoic 
acid,  and  proceeding  as  in  the  synthesis  of  terpineol. 

The  constitution  of  dipentene  is  derived  from  its  relation- 
ship to  terpineol  (p.  579),  from  which  it  is  obtained  by  the 
elimination  of  water.  If  molecular  rearrangement  does  not 
occur  during  this  reaction,  it  is  clear  that  dipentene  must  have 
a  constitutional  formula  corresponding  with  I  or  II: 


Terpineol 


Formula  I  is  not  asymmetric,  and  therefore  cannot  represent 
the  molecules  of  d-  and  Wimonenes  and  of  dipentene;  formula 
II,  on  the  other  hand,  contains  an  asymmetric  carbon  atom, 
the  one  indicated  by  an  asterisk,  the  molecule  is  asymmetric, 
and  can  form  d-t  Z-,  and  r-modifications. 

The  correctness  of  formula  II  is  confirmed  by  a  study  of 
some  of  the  reactions  of  dipentene. 

Dipentene  forms  a  nitroso-  chloride  (colourless),  and  this 
with  alkalis  gives  the  oxime  of  carvone.  The  oxime  when 
hydrolysed  yields  carvone,  and  this  on  reduction  yields  dihy- 
drocarveol,  a  secondary  alcohol  formed  by  the  addition  of  two 


PHELLANDRENES  577 

atoms  of  hydrogen  to  one  of  the  ethylene  linkings  and  two 
atoms  of  hydrogen  to  the  carbonyl  group.  Dihydrocarveol 
when  oxidized  yields  a  ketonic  alcohol,  CH3.C6H9(OH).CO- 
CH3,  proving  the  presence  of  the  •  C(CH3)  :  CH2  group  in  dihy- 
drocarveol,  carvone,  and  dipentene. 

Terpinolene  is  also  formed  from  terpineol  by  the  elimina- 
tion of  water,  and  should  therefore  be  represented  by  formula 
No.  I,  a  formula  which  is  in  harmony  with  the  inactivity  of 
the  hydrocarbon.  The  stable  terpinene  most  probably  con- 
tains conjugate  double  bonds,  and  as  it  is  formed  from  ter- 
pinoline  by  the  action  of  acids  it  is  probably  A-l:3-terpa- 
diene. 

Phellandrene.  —  Three  isomeric  phellandrenes  exist  in  nature  : 
d-a-phellandrene  in  oil  of  bitter  fennel  and  in  elemi  oil,  /-a-phel- 
landrene in  Australian  eucalyptus  oil  (Eucalyptus  amygdalina), 
and  d-/3-phellandrene  in  water  dropwort  (Phellandnum  aqua- 
ticum).  The  d-  and  /-a-phellandrenes  are  optical  antipodes, 
and  are  both  &-l:5-terpadienes.  The  b.-pt.  is  62°/12  mm.  It 
is  transformed  into  terpinene  by  the  action  of  acids,  and  its 
dibromide  with  alkalis  yields  cymene.  This  constitution  fol- 
lows from  the  fact  that  nitro-a-phellandrene,  when  carefully 
reduced,  yields  active  carvotanacetone,  A-5-terpene-2-one,  and 
has  been  confirmed  by  the  synthesis  of  a-phellandrene  from 
4-isopropyl-A2-hexenone  (A.  359,  285): 


Grignard 

—      C3H7  •  CH<™2  !  25>CMe, 

dehydrated 

and  also  by  its  synthesis  from  carvone  (p.  579). 

Carvone  —  ••  carvone  hydrobromide  •—  *•  A6-terpen-2-one  —  * 

IIBr  reduced  PC1S 

6-chloro-A-l  :  5-terpadiene  —  *•  a-phellandrene. 

reduced 

/3-Phellandrene  is  A-2  :  1  (l)-terpadiene.  It  has  boiling-point 
57°/ll  mm.,  yields  two  nitrosites,  melting-point  97°  and  102°. 
Its  constitution  is  based  on  the  fact  that  it  is  oxidized  by 
atmospheric  oxygen  to  4-isopropyl-A-2-hexenone  (A.  343,  29), 
and  on  its  synthesis  from  carvone  (J.  pr.  [ii],  72,  193;  75,  141). 

Carvone  —  -  carvomenthol  (terpane-2-ol)  —  *  A-1-terpene  —  * 

reduced  dehydrated  bromine 

terpenedibromide  —  *  /?-phellandrene. 

ale.  potash 
(B480)  ?0 


578  XLI.   TERPENES  AND   CAMPHORS 

Menthene,  obtained  from  menthol  by  the  elimination  of 
water,  is  A-3-terpene;  when  oxidized  it  yields  a  glycol,  which 
on  further  oxidation  gives  /2-methyladipic  acid  : 


It  has  been  synthesised  by  Wallach  (B.  39,  2504)  by  con- 
densing l-methylcyclohexan-4-one  with  ethyl  a-bromoiso- 
butyrate  and  zinc,  hydrolysing  and  eliminating  C02  and 
water. 

A  synthetical  terpene  or  dihydro-cymene  boiling  at  174°  has 
been  prepared  from  succinylo-succinic  ester  (pp.  342,  469) 
(B.  26,  233).  It  shows  the  complete  terpene  character,  has  a 
turpentine  odour,  becomes  resinous  on  exposure  to  the  air, 
decolorizes  permanganate  at  once,  and  takes  up  bromine. 

SUMMARY  OF  DERIVATIVES 

n«ninn  Tetra-       Dihydro-      xnt,™it« 

Bo^ng-  bromide,     chloride.     Nljj  * 

point.  M.p  M  _p  M.-p. 

Limonene...  175°  104°          50° 


Dipentene 

Terpinolene . . 

Terpinene 

Phellandrene. 
Sylvestrene... 


175°  125°  50° 

183°-185°  116° 

179°-181°  oil  oil          153° 

171°-172°  oil  oil          105° 

175°  135°  72° 


II.  Camphor  Compounds.  —  Alcohols  and  Ketones. 
Menthol,  3-terpanol,  mint  camphor,  C10H200  : 


The  /-modification  is  the  chief  constituent  of  oil  of  pepper- 
mint. It  melts  at  43°,  has  a  strong  odour  of  peppermint,  and 
is  used  as  an  antiseptic  and  anaesthetic.  When  heated  with 
copper  sulphate  it  yields  cymene,  when  reduced  with  hydriodic 
acid,  hexahydrocymene,  and  on  oxidation  with  permanganate 
it  yields  /3-methyladipic  acid,  and  several  fatty  acids.  As 
the  formula  contains  three  asymmetric  carbon  atoms,  several 
stereo-isomerides  are  possible. 

The  corresponding  ketone  menthone,  3-lerpanone,  010H18O, 
is  obtained  when  the  alcohol  is  oxidized  with  dichromate 
(Beckmann,  A.  1891,  262,  31),  and  also  occurs  in  oil  of  pepper- 
mint. It  boils  at  207°,  and  has  the  characteristic  properties 


TERPINEOL  579 

of  a  ketone;  its  semicarbazone  melts  at  184°.  It  is  readily 
converted  into  thymol  (l-methyl-3-hydroxy-4-isopropyl-ben- 
zene)  by  bromination  and  elimination  of  hydrogen  bromide, 
and  when  oxidized  yields  /?-methyladipic  acid.  Hence  follows 
the  constitution,  which  is  supported  by  its  synthesis  by  the 
distillation  of  calcium  /?-methyl-a'-isopropylpimelate  (Kotz  and 
Schwarz,  A.  357,  206): 

CHa  •  CHMe  •  CH2  •  CO(X  CH2  •  CHMe  —  CH2 

CH2.CH(C3Hr).COO— /  *    "        CH2.CH(C3H7).CO. 

An  unsaturated  ketone — pulegone,  A-4  (&)-terpene-3-one,  may 
be  obtained  from  oil  of  pennyroyal.  It  is  isomerie  with  ordi- 
nary camphor,  and  on  reduction  yields  menthone.  Its  con- 
stitution follows  from  the  fact  that  when  heated  with  water  it 
yields  acetone  and  methylcyclohexanone. 

Isomerie  with  menthol  is  carvomenthol  or  terpane-2-ol. 

Carvone,  A-6:8  (9)-terpadiene-2-one,  is  the  chief  constituent 
of  oil  of  carraway  seeds,  and  is  widely  distributed  in  the 
vegetable  kingdom.  It  is  a  liquid,  distils  at  228°,  exists  in 
d-and  /-modifications,  and  has  the  properties  of  an  unsaturated 
ketone  (cf.  A.  1897,  297,  122).  With  hydroxylamine  it  yields 
carvoxime,  which  is  identical  with  nitroso-limonene.  When 
heated  with  phosphoric  acid  carvone  is  isomerized  to  car- 
vacrol. 

Terpineol,  &-l-terpen-8-ol,  does  not  occur  in  large  quantities 
naturally,  but  is  obtained  readily  from  natural  products,  e.g.  by 
the  action  of  dilute  potash  on  limonene  hydrochloride,  or  by 
the  hydration  of  pinene  hydrate.  It  has  m.-pt.  37°,  b.-pt.  218°, 
and  [a]D  —  106°.  When  treated  with  dilute  acids  it  can  give 
dipentene,  terpinolene,  terpinene,  terpin  hydrate,  cineol  or 
cymene,  according  to  the  conditions.  Its  constitution  is  of 
importance,  as  those  of  several  terpenes  are  deduced  from  that 
of  terpineol.  The  constitution  is  based  on  (1)  examination  of 
its  decomposition  products,  (2)  its  synthesis. 

By  means  of  dilute  permanganate  two  hydroxyls  are  added 
to  the  double  bond,  and  l:2:8-trihydroxyterpane  (trihydroxy- 
hexahydro-jp-cymene)  is  formed,  and  this  on  further  oxidation 
yields  a  ketolactone,  homoterpenylic  methyl  ketone,  which  can 
be  oxidized  to  acetic  and  terpenylic  acids.  The  constitution 
of  the  latter  has  been  proved  to  be: 

,CH(CH2-CO2H).CH2 
CO 


CMe2<Q 


580  XLI.   TERPENES   AND   CAMPHORS 

from  its  method  of  synthesis  (Simonsen,  J.  C.  S.  1907,  184). 
This  gives  the  formula,: 

H(CH2  -  CH2  .  CO  •  CH3)  .  CH2 


for  homoterpenylic  methyl  ketone,  and  proves  the  l:2:8-posi- 
tions  of  the  three  hydroxyl  groups  in  the  first  oxidation  pro- 
duct, and  the  A-1-position  of  the  ethylene  linking  and  position 
8  of  the  hydroxyl  group  in  terpineol. 

Its  synthesis  (Perkin,  J.  C.  S.  1904,  654)  is  from  S-keto- 
hexahydrobenzoic  acid  (S-keto-cyclohexarie-carboxylic  acid). 
The  ester  of  this  acid  reacts  with  magnesium  methyl  iodide, 
and  then  with  water,  yielding: 

OH 


By  the  action  of  fuming  hydrobrornic  acid  the  hydroxyl  is 
replaced  by  bromine,  and  then  by  the  action  of  pyridine  hy- 
drogen bromide  is  eliminated  and  A-3-tetrahydro-p-toluic  acid 
is  formed.  The  ethyl  ester  of  this  acid  reacts  with  magnesium 
methyl  iodide,  and  then  with  water,  in  the  normal  manner, 
yielding  the  tertiary  alcohol,  inactive  terpineol: 


and  by  the  elimination  of  water  from  this  alcohol  dipentene 
was  obtained. 

This  method  of  synthesis  has  been  extended  by  Perkin  and 
his  students  to  a  large  number  of  cases,  and  they  have  obtained 
alcohols  and  unsaturated  hydrocarbons  analogous  to  the  natural 
products,  but  which,  so  far,  have  not  been  obtained  naturally. 
From  A-1-tetrahydro-^-toluic  acid,  A-3-j?-terpen-8-ol,  and  A-l  :  8 
(9)  terpadiene.  From  hexahydro-o-toluic  acid,  compounds  simi- 
lar to  terpineol  and  dipentene  were  obtained,  but  with  the 
substituents  in  o-positions.  From  hexahydrobenzoic  acid  a 
compound  was  obtained  analogous  to  dipentene,  but  without 
the  methyl  substituent  in  position  1.  By  using  optically 
active  A-1-tetrahydro-^-toluic  acid,  an  active  alcohol  and  ter- 
pene  were  synthesisecL  (Compare  J.  C.  S.  1905,  639,  655,  661, 
1067,  1083;  1906,  8*2,  839;  1908,  573,  1871,  1876;  1910, 
2129,  2147;  1911,  111,  518,  526,  727,  741.) 

Terpin,  p-terpurl  :  8-<*oJ,  has  been  synthesised  by  the  action 


COMPLEX  CYCLIC  TERPENES  581 

of  magnesium  methyl  iodide  on  both  carbonyl  groups  of  ethy 
cyclohexanone-4-carboxylate  (Kay  and  Perkin,  J.  C.  S.  1907 
372),  and  is  also  formed  by  boiling  terpineol  with  dilute  sul- 
phuric acid.     It  exists  in  two  stereoisomeric  modifications,  cis 
and  trans.     The  cis  is  the  common  form,  and  combines  with 
water  to  give  terpin  hydrate,   C10H2203,  which  forms  well- 
developed  crystals,  m.-pt.  116°.    When  dehydrated  the  terpins 
yield  terpinene,  terpinolene,  terpineol,  and  cineol;  the  latter  is 
an  inner  anhydride  (ether)  formed  by  the  elimination  of  water 
from  the  two  hydroxyl  groups. 

C.  Complex  Cyclic  Terpenes  and  Camphors 

The  compounds  belonging  to  this  group  are  bicyclic,  i.e.  the 
molecule  is  built  up  of  two  rings.  Benzene  or  reduced  ben- 
zene derivatives  containing  a  diagonal  linking  in  the  m-  or 
p-position  (examples  I  and  II)  are  bicyclic,  also  the  com- 
pounds which  can  be  regarded  as  derived  from  a  single  ring 
by  the  introduction  of  a  bridge  consisting  of  one  or  more 
carbon  atoms  (examples  III,  IV,  and  V). 

For  systematic  nomenclature  cf.  Baeyer,  B.  33,  3771. 


I.  Terpenes. — Pinene,  C10H16,  is  the  chief  constituent  of 
German  and  American  oil  of  turpentine,  oil  of  jumper,  euca- 
lyptus, oil  of  sage,  &c.  It  forms,  together  with  sylvestrene 
and  dipentene,  Russian  and  Swedish  turpentine  oil. 

Oil  of  turpentine  is  obtained  by  distilling  turpentine,  the 
resin  of  pines,  with  steam,  colophonium  (fiddle  resin)  remain 
ing  behind.  It  is  a  colourless,  strongly  refracting  liquid  of 
characteristic  odour,  almost  insoluble  in  water,  but  readily 
soluble  in  alcohol  and  ether.  It  dissolves  resins  and  caout- 
chouc (being  therefore  used  for  the  preparation  of  oil  paints, 
lakes),  also  sulphur,  phosphorus,  &c.  Pinene  absorbs  oxygen 
from  the  air  with  the  formation  of  ozone  arid  production  o* 
resin,  minute  quantities  of  formic  acid,  cymene,  &c.,  being 
formed  at  the  same  time.  Dilute  nitric  acid  gives  rise  eithei 
to  terephthalic  acid  in  addition  to  fatty  acids,  or — under  other 
conditions— to  terpeuylic  acid  (p.  579),  C8H1204  (which  belongs 


582  XLI.   TERPENES   AND   CAMPHORS 

to  the  fatty  series).  Heating  with  iodine  transforms  it  into 
cymene,  the  action  being  violent.  It  acts  as  an  antiseptic, 
and  arrests  the  secretions  (e.g.  that  of  the  kidneys). 

It  exists  in  three  stereoisomeric  modifications:  d-pinene  or 
australene  occurs  in  large  quantities  in  German,  Eussian,  and 
Swedish  oils;  /-pinene  or  terebenthene  in  French  turpentine 
oil;  tW-pinene  is  obtained  by  heating  pinene  nitroso-chloride 
with  aniline: 

[«]§"  E.-pt.  d4T 

d +45°        156°     0-858 

I —43-4°     156°     0-858 

d-l 0°        156°     0-858 

Pinene  has  all  the  characteristic  properties  of  an  unsaturated 
compound.  It  forms  a  nitroso-chloride  (C]0H16,  NOC1)2, 
colourless  crystals  melting  at  103°,  which  is  used  for  isolating 
pinene  from  mixtures;  also  a  hydrochloride,  C10H17C1,  a 
white  crystalline  solid  melting  at  131°,  with  a  camphor-like 
odour,  hence  the  name  "artificial  camphor".  This  is  in- 
soluble in  water,  but  readily  soluble  in  alcohol,  and  if  hydro- 
gen chloride  is  eliminated  by  weak  alkali,  e.g.  by  heating  it 
with  soap  or  with  silver  acetate,  camphene  is  obtained.  It  is 
identical  with  bornyl  chloride,  and  on  oxidation  yields  cam- 
phoric and  apocamphoric  acid.  It  is  probable  that  by  conver- 
sion into  the  hydrochloride  an  intramolecular  rearrangement 
has  taken  place,  as  indicated  by  the  following  formulae: 

CMeCl  CMe 

H20      |  ^XjHCl 
—  CMea    I 

H2C^  I       CH2 

CH 

Pinene  Intermediate  Pinene 

Product  hydrochloride 

The  presence  of  a  double  bond  in  the  pinene  molecule  is 
indicated  by  the  formation  of  dibromides,  an  oil  and  a  solid 
melting  at  169°,  and  also  by  the  formation  of  a  glycol,  pinene 
glycol,  C10Hi6(OH)2,  by  the  action  of  dilute  permanganate. 

The  constitution  of  pinene  is  based  largely  upon  that  of 
pinole,  CjoHjgO,  a  product  obtained  by  the  elimination  of 
water  from  soberol,  Ci0H16(OH)2,  which  is  formed  when  pinene 
is  left  exposed  to  sunlight  in  contact  with  air  and  water.  With 


COMPLEX  CYCLIC  TERPENES  * 


583 


dilute  permanganate,  pinole,  which  is  an  unsaturated  ether, 
yields  pinoleglycol,  010H]60(OH)2,  and  this  on  further  oxida- 
tion yields  a  tetrahydric  alcohol,  sobrerythritol,  C10H16(OH)4, 
which  can  be  oxidized  to  terpenylic  acid.  Pinole  presumably 
contains  the  same  grouping  of  carbon  atoms  as  terpenylic  acid 
(see  p.  579),  and  should  be  either: 


CH=CMe— CH 


cf 


CHa—  dH  — 


CH2— CMe— C 

0 


or 


Sobrerol  would  then  be : 

CH= CMe CH  •  OH 

I    I          6Me2.QH  I 

O  tl-2 — Oxi  OJEL2 


or 


CH2— CMe=C-OH 
(*Me2.OH  I 
-CH CH, 


but  since  sobrerol  on  further  oxidation  yields  a  tetrahydric 
alcohol  and  not  a  dihydroxy-ketone,  formula  I  is  correct,  and 
the  formula  on  p.  582  follows  for  pinene  (Wagner). 

When  boiled  with  dilute  acids  pinene  yields  terpineol  or  its 
esters;  such  a  transformation  is  explicable  if  the  assumption 
is  made  that  the  four-membered  ring  is  unstable,  and  that  a 
rupture  between  the  CMe2  and  upper  CH  -group  occurs.  A 
similar  rupture,  accompanied  by  the  wandering  of  a  chlorine 
atom,  occurs  in  the  transformation  of  pinene  nitroso-chloride 
into  hydrochlorocarvoxime  under  the  influence  of  hydrochloric 
acid. 

When  pinene  is  oxidized  with  permanganate  the  double  link« 
ing  is  broken  and  a  monobasic  ketonic  acid,  pinonic  acid, 


is  formed,  and  this  on  further  oxidation  yields  the  dibasic 
acid  pinic  acid, 


from  which  nor  pinic  acid,  1:1  -dimethyl-  cyclobutane-2  :  4-dicar- 
boxylic  acid,  can  be  obtained  (Baeyer,  B.  29,  1907),  indicating 
that  the  four-membered  ring  is  stable  in  the  presence  of 


584  XLI.    TERPENES   AND   CAMPHORS 

oxidizing  agents,  although  readily  ruptured  by  hydrolysing 
agents,  e.g.  pinonic  acid  yields  when  hydrolysed  a  lac  tone, 
homoterpenylic  methyl  ketone  (cf.  p.  580). 


OH  -  CO  •  C  JI2  •  CH>CH  .  CO  •  CH3 


The  only  reactions  of  pinene  difficult  to  account  for  by 
means  of  Wagner's  formula  are  its  oxidation  to  isoketocam- 
phoric  acid,  isocamphoronic  acid,  and  terebic  acid  (Tiemann 
and  Semmler,  B.  29,  529,  3027;  Perkin,  Proc.  1900,  214). 

Bornylene  is  obtained  by  the  action  of  alkalis  on  bornyl 
iodide  (from  pinene  and  hydrogen  iodide),  and  as  it  is  readily 
oxidized  to  camphoric  acid  it  is  represented  by  formula  I. 

The  corresponding  saturated  hydrocarbon  camphane,  CjnHjg, 
the  parent  substance  of  the  camphor  group,  is  obtained  by 
reducing  bornyl  iodide.  It  melts  at  154°,  and  is  optically 
inactive;  its  molecule  should  therefore  be  symmetrical. 

CH2.CMe-CH  CH2.CMe-CO  CH2.CMe.CO2H 

I   I        CMe2  1!  II   I        CMe2  I  III   I        CMe2 

CH2-CH—  CH  CH2.CH—  CH2  CH2.CH—  CO2H 

Bornylene  Camphor  Camphoric  acid. 

Camphene,  d  and  Z,  is  a  solid,  m.-pt.  50°.  It  can  be  obtained 
from  pinene  by  combining  with  hydrogen  chloride,  forming 
bornyl  chloride,  and  then  removing  hydrogen  chloride  by 
means  of  alkalis.  For  some  years  it  was  represented  by 
formula  I,  but  it  does  not  yield  camphoric  acid  when  oxidized. 
Harries  and  Palmer  (B.  1910,  43,  1432)  have  shown  that  it 
forms  an  ozonide  when  its  acetic  -acid  solution  is  saturated 
with  ozone,  and  that  this  when  warmed  yields  a  mixture  of 
camphenilone  (30  per  cent)  (IV), 

CMe2.CH-CH2  CMe2.CH.CH2  CMe2.CH-CH2 

IV   I         CH2  I  V  6         CH2  I  VI   I         CH2  I 

CO  —  CH.CH2  CO  —  CH.CH2     CH2:C  -  CH-CH2 

and  rf-hydroxy-camphenilic  acid  lactone  (50  per  cent)  (V),  and 
they  therefore  suggest  formula  VI  for  camphene.     The  for- 


CAMPHORS  585 

tnation  of  camphene  from  bornyl  chloride  must  thus  involve 
molecular  rearrangements. 

Sabinene  occurs  in  marjoram  oil;  it  has  b.-pt.  163°-165° 
and  [a],,  -f-  80°.  It  forms  a  hydrochloride  and  a  nitroso- 
chloride;  when  oxidized  it  yields  a  ketone  by  the  replacement 
of  CH2  by  0,  and  therefore  probably  contains  a  methylene 
group  attached  to  the  nucleus.  It  also  probably  contains 
a  three-membered  ring  and  is  represented  as 


The  tri-ring  is  readily  ruptured,  as  sabinene  and  its  deriva- 
tives can  be  transformed  into  terpinene  and  related  hydroxy 
compounds,  a  and  /?  Thujenes,  C10H16  (Tschugaeff,  B.  34, 
2279;  37,  1481),  also  contain  a  tri-ring  and  a  double  linking 
in  positions  1  and  3  respectively. 

II.  Camphors. — The  most  important  variety  of -camphor 
is: 

Common  or  Japan  camphor,  C]0H160,  which  is  found  in 
the  camphor  tree  (Laurus  camphora),  and  can  be  obtained 
from  the  latter  by  distillation  in  steam.  It  forms  colourless, 
transparent,  glistening  prisms  of  characteristic  odour.  It  melts 
at  175°,  boils  at  204°,  has  a  sp.  gr.  0-985,  and  can  be  sublimed 
readily.  It  is  dextro-rotatory  in  alcoholic  solution,  the  amount 
of  rotation  varying  with  the  source  of  the  camphor.  When 
distilled  with  phosphoric  anhydride  it  yields  cymene;  zinc 
chloride  at  high  temperatures  also  transforms  camphor  into 
cymene,  though  in  the  latter  case  the  reaction  is  less  simple: 

C10H160  =  C]0H14  +  H20. 

When  heated  with  iodine  it  yields  carvacrol,  i.e.  hydroxy- 
cymene  (p.  417),  just  as  oil  of  turpentine  yields  cymene.  Nitric 
acid  oxidizes  it  to  the  dibasic  camphoric  acid,  C8HU(C02H)2, 
which  somewhat  resembles  phthalic  acid  (see  R  23,  218),  and 
then  to  camphoronic  acid,  unsym.  trim e thy  1-carbally lie  acid, 
&c.  Camphor  reacts  with  hydroxylamine  to  produce  cam- 
phor-oxime,  C]0H1§(NOH),  and  therefore  contains  a  carbonyl 
group,  and  with  nitrous  acid  to  produce  isonitroso- camphor, 
C10H140:N-OH,  and  thus  contains  the  group  •  CH2«CO. 
The  oxime  by  the  loss  of  water  is  converted  into  the  cyanide, 
09H15»CN,  which  yields  campholenic  acid,  C^I^COjH,  on 


686  XLt  TERPENES  AND  CAMPHO&S 

saponification,    and    camphylamine,    C9H16(CH2  •  NH2),    on 
reduction  (B.  21,  1125). 

A  considerable  amount  of  attention  has  been  devoted  by 
various  chemists  to  the  question  of  the  constitution  of  cam- 
phor (Lapworth,  B.  A.  Report,  1900,  299).  At  first,  great  im- 
portance was  attached  to  the  readiness  with  which  camphor 
can  be  transformed  into  benzene  derivatives,  e.g.  cymene  and 
carvacrol,  and  attempts  were  made  to  represent  it  as  a  simple 
six-carbon  ring  compound,  e.g.  KekuU. 

•CO 


whereas  others  represented  it  as  a  bridged  six-carbon  ring. 
In  1893  Bredt  suggested  the  formula  II  (p.  584),  which  is  now 
generally  accepted,  and  which  has  been  confirmed  recently  by 
the  synthesis  of  camphoric  acid.  Bredt  drew  especial  atten- 
tion to  the  oxidation  products  of  camphor,  namely  camphoric, 
camphoronic,  and  trimethyl-succinic  acid  previously  obtained 
by  Koenigs.  He  showed  that  camphoronic  acid  when  heated 
gave  trimethyl-succinic,  isobutyric,  and  carbonic  acids  and 
carbon,  and  suggested  the  formula  C02H'CH2-CMe(C02H)« 
CMe2»C02H,  viz.  a-a-j8-trimethyl-carballylic  acid,  a  consti- 
tution which  has  since  been  confirmed  by  W.  H.  PerJcin  and 
Thorpe's  synthesis  (J.  C.  S.  1897,  1169).  This  consists  in 
condensing  ethyl  acetoacetate  and  ethyl  a-bromo-isobuty- 
rate  by  means  of  zinc  to  ethyl  /?-hydroxy-a-a-/2-trimethyl 
glutarate  : 

CBrMe2  •  COJ&t  CMe2  •  CO2Et 

CHs.CO.CH2.CO2Et  ~*  OH.CMe-CH2.CO2Et. 

The  OH  group  is  replaced  by  Cl,  and  this  by  ON,  and  the 
cyano-ester  when  hydrolysBd  yields  camphoronic  acid  : 


CMe2.C02Et 
CN.CMe.CH8.C02Et 

The  relationship  between  camphor  and  its  oxidation  products 
is  thus  simple,  as  shown  by  the  following  scheme  :  — 

CH2.CMe.CO          CH2.CMe.C02H(/S)         CH2—  CMe2.002H 
CMe2|      -*  CMe2  -*   I          CMe2 

CH2.CH—  CH2        CH2.CH—  CO2H(a)         CO2H  CO2H 

Camphor  Camphoric  acid  Camphoronic  acid. 


CAMPHORS  587 

Camphoric  acid  has  been  synthesised  by  Komppa  (B.  1901, 
34,  2472;  1903,  36,  4332).  Ethyl  oxalate  and  ethyl  /3/?-di- 
methyl-glutarate  condense  in  the  presence  of  sodic  ethoxide, 
yielding  diketo-apocamphorate : 

H  •  CH  •  CO2Et  CO .  CH  •  C02Et 


C 
CO-C 


CMe2 
H-CH.C02Et  CO.CH.C02Et. 

This  is  methylated  by  means  of  sodium  and  methyl  iodide, 
and  the  ethyl  ester  of  diketo-camphoric  acid  thus  obtained, 

>.CH.CO2Et 
CMe2 


I 


may  be  reduced  with  sodium  amalgam  to  dihydroxy-camphoric 
acid;  and  this,  in  its  turn,  with  phosphorus  and  hydriodir 
acid  to  dehydro-camphoric  acid, 

CH.CH.CO2Et 
CMe2 
.CMe-CO,Et, 

which  combines  with  hydrogen  bromide;  and  the  /3-bromo- 
camphoric  acid  thus  obtained,  when  reduced  with  zinc  and 
acetic  acid,  yields  the  racemic  modification  of  camphoric  acid. 
Camphor  can  be  synthesised  from  camphoric  acid  by  the 
following  series  of  reactions  (Holler,  C.  R  1896,  122,  446): 


I 


Camphoric  Campholide  Homocamphoric 

anhydride  nitrile 

/COOH 


Homocamphoric  acid     distilled       Camphor, 

Considerable  amounts  of  camphor  are  manufactured  from 
pinene  by  the  following  series  of  reactions: 

Pinene   —  *   Bornyl  chloride    —  »•    Isobornyl  acetate 

HCl  Metallic 

acetate 

—  ••     Isoborneol     —  *     Camphor. 
hydrolysed  oxidised 

(Cf,  Iloiisemann,  Sci.  Progress,  No.  9.) 


588  XLI.    TERPENES   AND   CAMPHORS 

Camphoric  acid  is  an  unsymmetrical  dibasic  acid,  as  it  gives 
two  isomeric  monometbyl  esters  and  two  amic  acids.  One 
carboxylic  acid  is  probably  attached  to  a  tertiary  and  the 
other  to  a  secondary  carbon  atom,  as  the  acid  yields  a  single 
monobromo  substituted  derivative  when  subjected  to  the  Hell- 
Volhard-Zelinsky  method  of  bromination.  The  derivatives  are 
known  respectively  as  a  and  fi  (or  ortho  and  allo),  the  a- 
methyl  ester,  for  example,  contains  the  group  ^>CH*C02Me, 

and  the  /?- methyl  ester  the  group  ^C  •  C02Me.  As  isonitroso- 
camphor — C(:NOH)«CO — when  warmed  with  hydrochloric 
acid  yields  a-camphoramic  acid,  \CH.CO«NH2,  it  follows 
that  the  methylene  group  of  camphor  corresponds  with  the 
a-carboxylic  group  in  camphoric  acid. 

Camphoric  acid  exists  in  four  optically  active  and  two 
racemic  modifications,  the  latter  known  respectively  as  r-cam- 
phoric  and  r-isocamphoric  acids.  This  points  to  the  presence 
of  two  asymmetric  carbon  atoms  in  the  molecule  of  the  acid, 
as  indicated  in  the  formula.  Camphor,  on  the  other  hand, 
exists  in  two  active  and  one  racemic  form  only.  When  d- 
camphoric  acid  is  racemized  the  product  is  not  r-camphoric 
acid,  but  a  mixture  of  the  original  acid  with  Z-iso-camphoric 
acid.  This  is  due  to  the  fact  that  only  one  asymmetric  car- 
bon atom  is  concerned  in  the  racemization.  In  the  oxidation 
of  camphoric  acid  to  camphoronic  acid,  camphanic  acid,  the 
lactone  of  a-hydroxy-camphoric  acid  is  formed  as  an  intei- 
me/3iate  product;  its  constitution  follows  from  the  fact  that  it 
is  formed  by  boiling  bromo-camphoric  anhydride  with  water. 

.C^—-  CO2H 

GMe2  O  Camphanic  acid. 

2-CMe-CO 

Various  chloro-,  bromo-,  nitro-,  and  ammo-camphors  are 
known. 

Borneol  or  Borneo  camphor,  C10Hir.OH,  occurs  in  nature 
(in  Dryobalanops  camphora),  and  is  produced  by  the  action  of 
nascent  hydrogen  upon  Japan  camphor: 

C10H160  +  2H  =  C10H180. 
It  resembles  the  latter,  but  has  at  the  same  time  an  odour 


IRONE.      IONONES  589 

of  pepper.  It  crystallizes  in  hexagonal  plates,  melts  at  208°, 
boils  at  212°,  and  when  oxidized  yields  in  the  first  instance 
camphor.  Borneol  possesses  the  character  of  a  secondary 
alcohol,  yielding  esters,  and  with  PC15  yields  bornyl  chloride, 
C10Hi7Cl  (m.-pt.  148°),  which  is  identical  with  pinene  hydro- 
chloride;  bornyl  chloride  yields  camphene  when  warmed  with 
alkalis. 

D.  Compounds  related  to  Terpenes 

Irone — a  methyl  ketone,  C13H200 — is  the  odoriferous  prin- 
ciple of  the  iris  root,  and  also  probably  of  the  violet.  When 
boiled  with  hydriodic  acid  it  yields  the  hydrocarbon  irene, 

GIS^IS- 
The  formulae  suggested  for  these  compounds  are : 


/  *  /CH 

CH-CH:CH-COMe      HC 


CMe,     ^C 
C  CH 


CH2 


II  -Me 

CH2  CH 

Irone  Irene 


(cf.  Tiemann  and  Kriiger,  B.  26,  2675).  These  chemists  have 
synthesised  two  isomerides  of  irone,  which  they  term  a-  and 
/3-ionones.  .  s, 

These  also  possess  the  odour  of  violets,  and  are  employed 
it  the  present  time  for  the  manufacture  of  violet  essence. 

The  synthesis  consists  in  the  condensation  of  citral  (p.  570) 
with  acetone  to  form  the  unsaturated  ketone  pseudo-ionone : 


CMe2:CH.CH2.CH2.CMe:CH.CH;0  +  H?;C 

=  CMe2  :  CH  •  CH2  •  CH2  •  CMe  :  CH  .  CH  :  CH  •  COMe, 

which  is  transformed  into  the  ring  compounds  a-  and  /2-ionones 
when  boiled  with  sulphuric  acid  : 


CMe2  CMe2 


H2CC.CH:CH.COMe 


Cll  CH2 

a-Ioaone 


590  XLI.   TERPENES  AND  CAMPHORS 

Carone,  C10H160,  is  one  of  the  most  important  ring  ketones 
of  the  terpene  series,  and  is  formed  when  dihydrocarvone 
hydrobromide,  8-bromoterpane-2-one,  is  treated  with  alcoholic 
potash  (Baeyer,  B.  1896,  29,  5  and  2796). 

CHMe  CHMe 

— "  nt  T%I 

CBrMe2  CH 

It  is  a  colourless  oil  with  an  odour  of  camphor  and  pepper- 
mint, and  boils  at  210°,  but  is,  at  the  same  time,  partially 
transformed  into  the  isomeric  carvenone.  The  molecule, 
according  to  Baeyer,  contains  a  six-carbon  ring  with  a  bridge, 
so  that  it  is  divided  into  a  penta-  and  a  tri-methylene  ring. 
One  of  the  most  characteristic  properties  is  the  readiness 
with  which  the  bridge  is  broken  and  derivatives  of  p-  or 
wi-terpane  are  produced.  Thus  when  heated  it  yields  car- 
venone or  A-3-^-terpene-2-one, 


with  hydrobromic  acid  it  yields  8-bromoterpane-2-one,  and 
\vith  sulphuric  acid  8-hydroxy-terpane-2-one, 


When  oxidized,  carone  yields  a  dibasic  acid,  caronic  acid 
(cis  and  trans  modifications),  which  Baeyer  suggested  was 
dimethyl-trimethylene  dicarboxylic  acid, 


CMe2< 

XCH-C02H, 

a  conclusion  which  has  been  confirmed  by  Perkin's  synthesis 
(J.  C.  S.  1899,  48).  In  this  synthesis  ethyl  dimethylacrylate, 
CMe2:CH.C02Et,  is  condensed  with  ethyl  sodio-malonate  (or 
ethyl  sodio-cyanoacetate),  and  the  product,  ethyl  dimethyl- 
propane-tricarboxylate,  (COl2Et)2CH.CMe2.CH2-C02Et,  when 
hydrolysed  and  heated  at  200°,  yields  ft8-dimethyl  glutaric 
acid,  C02H-CH2.CMe2.CHo-C02H.  The  a-bromo-derivative 
of  the  ethyl  ester  of  this"acid/C02Et.CHBr.CMe2.CH2.C02Et> 


RESINS  591 


yields  cis  and  trans  caronic  acids  when  heated  with  alcoholic 
potash: 

CMe2  CMe2 

COaEt.HCBr  HCH.CO.jEt      *  COjH-HC — CH.(X)aH. 


XLII.   RESINS;  GLUCOSIDES 
A.  Resins 

Many  organic  compounds,  the  terpenes  in  particular,  possess 
the  property  of  becoming  "  resinified  "  by  oxidation  in  the  air 
or  under  the  influence  of  chemical  reagents,  i.e.  of  being  con- 
verted into  substances  very  similar  to  the  resins  which  occur 
in  nature.  These  natural  resins  are  solid,  amorphous,  and 
generally  vitreous  brittle  masses  of  conchoidal  fracture,  in- 
soluble in  water  and  acids,  but  soluble  in  alcohol,  ether,  and 
oil  of  turpentine.  They  are  found  naturally  in  abundance, 
partly  also  as  balsams,  i.e.  dissolved  in  terpenes  or  ethereal 
oils,  from  which  they  can  be  separated  by  distilling  in  steam. 
The  resins  dissolve  in  alkalis  to  form  compounds  of  the  nature 
of  soap  (resin  soaps),  being  again  precipitated  from  the  aqueous 
solutions  of  these  on  the  addition  of  acids;  most  resins  must 
therefore  consist  of  a  mixture  of  somewhat  complicated  acids 
(the  so-called  resin-acids). 

Abietic  acid,  C19H28O2,  has  been  isolated  from  colophonium 
(the  residue  from  the  distillation  of  turpentine);  it  crystallizes 
in  small  plates,  melts  at  153°,  and  is  soluble  in  hot  alcohol. 
Pimaric  acid,  C20HS002,  has  been  prepared  from  galipot  resin 
(Pinus  maritima)  in  a  similar  way.  It  melts  at  144°-146°, 
and  closely  resembles  abiotic  acid. 

The  resins  show  their  relation  to  the  aromatic  compounds 
by  their  conversion  into  hydrocarbons  of  the  benzene  or 
naphthalene  series  when  distilled  with  zinc  dust,  and  by  the 
formation  of  di-  and  trihydroxy-benzenes  when  they  are  fused 
with  potash. 

In  addition  to  colophonium,  there  may  be  mentioned  among 
other  resins  shellac  (from  East  Indian  Ficus  varieties),  and 
amber,  a  fossil  resin  which  contains  succinic  acid  in  addition 
to  resin-acids  and  a  volatile  oil. 

The  resins  are  largely  used  for  the  manufacture  of  lacs, 
varnishes,  &c. 


592  XLII.  RESINS;  GLUCOSIDES 

B.  Glueosides 

Glucoside  is  the  name  given  to  a  number  of  complex  organic 
compounds  which  occur  in  vegetable  tissues.  They  are  all 
characterized  by  the  fact  that  on  hydrolysis  with  acids,  alkalis, 
or  enzymes,  a  sugar — usually  ^-glucose — is  formed.  They  are 
therefore  to  be  regarded  as  anhydro-compounds  of  d-glucose 
or  some  other  sugar  with  various  organic  compounds. 

In  addition  to  these  natural  glucosides,  the  constitutions  ol 
which  are  unknown,  E.  Fischer  has  prepared  artificially  simplei 
glucosides,  of  the  type  of  a-  and  /3-methyl-glueosides  (p.  310) 
by  the  action  of  methyl  alcohol  and  hydrogen  chloride  on 
glucose.  These  are  probably  stereoisomeric  compounds: 

OCH3  -  CH[CH  •  OH]2 .  CH  •  CH(OH) .  CH2 .  OH. 

The  a-compound  melts  at  165°  and  the  ft-  at  107°.  They  do 
not  reduce  Fehling's  solution,  and  on  hydrolysis  yield  ^-glucose 
and  methyl  alcohol. 

Among  the  commoner  natural  glucosides  are: 

Amygdalin,  C^H^C^N  (p.  423),  found  in  bitter  almonds, 
in  the  leaves  of  the  cherry  laurel,  in  the  kernels  of  the  peach, 
cherry,  and  other  Amygdalacese.  It  crystallizes  in  colourless 
prisms,  melts  at  200°,  is  readily  soluble  in  water,  and  on  hy- 
drolysis with  emulsin  yields  benzaldehyde,  ^-glucose,  and  hy- 
drogen cyanide.  Emulsin  is  an  enzyme  which  occurs  in  bitter 
almonds.  It  is  characteristic  of  most  glucosides  that  in  the 
plant  tissue  they  are  accompanied  by  an  enzyme,  which  is  able 
in  the  presence  of  water  to  hydrolyse  them.  Amygdalin  may 
also  be  hydrolysed  by  dilute  mineral  acids. 

With  concentrated  hydrochloric  acid  it  yields  Z-mandelic 
acid,  and  with  an  enzyme  contained  in  yeast  (amygdalase) 
it  yields  glucose  and  /-mandelonitrile-glucoside. 

Isoamygdalin,  obtained  by  the  action  of  alkalis  on  amyg- 
dalin,  is  the  racemic  form  of  which  ordinary  amygdalin  is 
the  /-modification.  Amygdalin  is  the  commonest  of  the  cyano- 
genetic  glucosides,  i.e.  glucosides  which  give  rise  to  hydrogen 
cyanide  in  plant  tissues  or  on  hydrolysis.  Some  of  the  other 
members  are:  dhurrin,  p - hydroxy-mandelonitrile - glucoside 
(Dunstan  and  Henry},  in  the  great  millet;  phaseolunatin,  ace- 
tone-cyanohydrine-a-glucoside,  in  beans  of  Phaseolus  lunatus; 
iotusin  from  Lotus  arabicus. 

Salicin,  C18H18O7,  found  in  varieties  of  Salix,  is  hydrolysed 


GLUOOSIDES  593 

to  saligenin  (o-hydroxy-benzyl  alcohol)  and  dextrose;  populin 
or  benzoyl-salidn,  C10H2208  (in  varieties  of  Populus),  can  be  pre- 
pared artificially  from  benzoyl  chloride  and  salicin. 

Arbutin,  C12H1607,  and  methyl-arbutin,  C13H1807,  present 
in  the  leaves  of  the  bear-berry,  &c.,  yield  glucose  and  quinol 
or  methyl-quinol  respectively.  Methyl-arbutin  has  been  syn- 
thesised  by  Michael  (B.  1881,  14,  2097)  from  acetochloro- 
glucose  and  quinol  methyl  ether. 

Hesperidin,  C22H26012,  which  is  contained  in  unripe  oranges, 
&c.,  can  be  decomposed  into  glucose,  hesperetic  acid  (isomeric 
with  ferulic  acid,  p.  464),  and  phloroglucinol. 

Phloridzin,  C21H24O10,  found  in  the  bark  of  fruit-trees, 
yields  grape-sugar  and  phloretin,  C15H14O5  (B.  1895,  28,  1393), 
and  this  latter,  in  its  turn,  phloretic  acid  and  phloroglucinol 
(p.  420).  Both  induce  glycosuria  (i.e.  a  functional  derangement 
of  the  liver,  giving  rise  to  temporary  diabetes)  in  animals. 

Aesculin,  C15H1609,  present  in  the  bark  of  the  horse-chestnut, 
is  decomposed  by  acids  into  grape-sugar  and  Aesculetin  (di- 
hydroxy-coumarine),  C9H1604. 

Digitonin,  digitalin,  and  digitalei'n  are  three  glucosides 
which,  together  with  digitoxin  (the  most  important  constituent 
from  a  pharmacological  point  of  view),  are  present  in  the  digi- 
talis of  commerce  (cf.  B.  24,  339;  25,  Ref.  680;  31,  2454). 

Coniferin,  C16H2208  +  2H20,  contained  in  the  cambium  sap 
of  the  Coniferae,  yields  glucose  and  coniferyl  alcohol  on  hy- 
drolysis, and  serves  for  the  preparation  of  vanillin  (p.  430). 

Indican  (p.  526)  is  indoxyl-glucoside. 

Syringin,  the  glucoside  of  Syringa,  is  a  methoxy-coniferin. 

Myronic  acid,  C10Hi709NS2,  is  present  as  potassium  salt 
(Sinigrin),  C^H^KOgNS*  H20  (glistening  needles),  in  black 
mustard  seed.  It  is  hydrolysed  by  baryta  water,  or  by  my- 
rosin,  an  enzyme  present  in  mustard  seed,  to  grape-sugar, 
potassium  bisulphate,  and  allyl  isothiocyanate  (p.  277). 

(For  list  of  natural  glucosides  cf.  Armstrong,  "  Simple  Carbo- 
hydrates and  Glucosides  ",  p.  80.) 


XLIII.  ALBUMINS;   PHYSIOLOGICAL  CHEMISTRY 

An  extended  description  of  the  substances  (other  than  those 
already  mentioned)  which  are  found  in  the  animal  organism,  and 
which  are  therefore  of  importance  for  physiological  chemistry, 

(BttO)  «* 


594          XLIII.   ALBUMINS;    PHYSIOLOGICAL  CHEMISTRY 

will  not  be  attempted  here,  since  they  are  for  the  most  part 
better  known  from  a  physiological  than  from  a  chemical  point 
of  view.  Only  the  albumins  and  some  of  the  substances  which 
are  produced  during  metabolic  processes  will  be  dealt  with. 

Albumins 

For  an  account  of  the  modern  views  of  the  chemistry  of 
albumins  see  A.  Kossel  (B.  1901,  34,  3214;  E.  Fischer,  B.  1906, 
39,  530). 

The  albumins  make  up  the  chief  part  of  the  organism,  being 
present  partly  in  the  soluble  and  partly  in  the  solid  state; 
they  are  found  in  protoplasm  and  in  all  the  nutritive  fluids  of 
the  body.  In  the  tissues  of  green  plants  the  albumins  are 
synthesised  in  quite  unknown  ways  from  simple  substances 
like  carbon  dioxide,  water,  ammonium  nitrate  and  sulphate. 
(Cf.  Meldola,  J.  C.  S.  1906,  749.)  The  majority  of  albumins 
are  insoluble  in  water,  but  dissolve  in  dilute  saline  solutions. 
Their  presence  in  the  juices  of  the  animal  organism  is  prob- 
ably due  to  saline  and  other  substances.  In  solution  they 
are  opalescent,  laevo-rotatory,  and  do  not  diffuse  through  parch- 
ment paper,  i.e.  are  colloids;  but  they  are  thrown  down 
when  the  solution  is  warmed,  or  upon  the  addition  of  strong 
mineral  acids,  of  many  metallic  salts  [e.g.  copper  sulphate, 
basic  lead  acetate,  and  mercuric  chloride],  of  alcohol,  tannic 
acid,  acetic  acid  together  with  a  little  potassium  ferrocyanide, 
picric  acid,  or  phosphotungstic  acid.  They  are  insoluble  in 
alcohol  or  ether,  and  their  solutions  are  usually  precipitated 
("salted  out")  by  the  addition  of  ammonium  sulphate,  and 
mixtures  of  different  albumins  can  often  be  fractionally  pre- 
cipitated by  gradually  increasing  the  concentration  of  the 
ammonium  sulphate.  This  concentration  is  definite  for  each 
albumin,  as  is  also  its  temperature  of  coagulation.  Proteins 
can  also  be  coagulated  by  treatment  with  absolute  alcohol  or 
with  boiling  water.  After  coagulation  all  albumins  become 
insoluble  in  neutral  solvents,  but  dissolve  in  alkalis  or  acids, 
yielding  metaproteins,  which  are  also  formed  by  boiling  the 
uncoagulated  albumins  with  acetic  acid  or  alkali.  When 
boiled:  (a)  with  nitric  acid,  they  are  coloured  yellow  (the 
xantho- protein  reaction);  (b)  with  a  solution  of  mercuric 
nitrate  containing  nitrous  acid  (Milloris  reagent),  red;  (c)  with 
caustic  soda  solution  and  a  very  little  cupric  sulphate,  violet. 

Many  of  the  albumins  have  been  prepared  pure,  although 


ALBUMINS  595 

this  is  a  very  difficult  operation.  With  the  exception  of  the 
crystalline  albumin  which  occurs  in  hemp,  castor -oil,  and 
pumpkin  seeds  (B.  15,  953),  and  the  recently  isolated  crystal- 
line egg  albumin  and  serum  albumin  (B.  24,  Ref.  469;  25, 
Ref.  173),  they  do  not  crystallize. 

The  different  albumins  vary  only  slightly  among  themselves 
in  percentage  composition;  they  contain: 

C  =  52-7  to  54-5  p.c.;  H  =  6'9  to  7'3  p.c.;  N  =  16'4  to  17'6  p.c.; 
O  =  20*9  to  23'5  p.c. ;  and  S  =  0'8  to  5'0  p.c. 

It  is  impossible  at  present  to  construct  a  formula  from  these 
numbers,  and  even  approximate  molecular  weights  have  not 
been  determined. 

The  fact  that  albumin  contains  sulphur  is  worthy  of  note, 
though  the  mode  in  which  it  is  combined  in  the  molecule  is 
unknown;  warming  with  a  dilute  alkaline  solution  is  sufficient 
to  eliminate  it  partially,  e.g.  when  white  of  egg  is  boiled  with 
an  alkaline  solution  of  lead  oxide,  sulphide  of  lead  is  precipi- 
tated (the  test  for  sulphur  in  albumin). 

Albumin  preparations  usually  leave  a  very  considerable 
amount  of  ash,  i.e.  inorganic  salts,  on  incineration.  It  is  not 
yet  certain  in  how  far  this  mineral  matter  forms  an  integral 
constituent  of  these  substances;  but  the  properties  of  "egg 
albumin  free  from  ash  "  are  materially  different  from  those  of 
ordinary  albumin  (B.  25,  204). 

Although  the  constitution  of  no  single  albumin  has  been 
determined,  a  considerable  amount  of  work  has  been  done  in 
this  direction,  more  especially  by  an  examination  of  the 
simpler  products  obtained  when  the  albumins  are  (a)  oxidized, 
(b)  hydrolysed,  and  (c)  fermented  by  micro-organisms. 

(a)  The  products  obtained  on  oxidation  consist  largely  of 
volatile  fatty  acids,   their   aldehydes,    ketones,   and   nitriles, 
together  with  hydrogen  cyanide  and  benzoic  acid. 

(b)  The  usual  hydrolytic  agents  used  are  (1)  baryta  water, 
(2)  hydriodic  acid,  (3)  concentrated  hydrochloric  acid,  and 
(4)  sulphuric  acid  (25  per  cent).     The  last  of  these  appears  to 
be  the  best,  as  it  produces  less  complex  decomposition,  e.g. 
less   ammonia    and    more   amino- acids.     The    most   marked 
feature  of  the  products  thus  obtained  is  the  predominance 
of  amino-acids. 

The  list  of  compounds  which  have  been  isolated  from  the 
hydrolytic  products  is  as  follows:  (i)  Ammonia;  (ii)  car- 
bamide; (iii)  diamino-acids;  (iv)  monamino-acids;  (v)  pyr- 


596  XUII.   ALBUMINS;    PHYSIOLOGICAL  CHEMISTRY 

rolidine  -  2  -  carboxylic   acid  (proline),  HN<  •    2, 

M^ii(L'U2il)  •  Url2 

and  its  hydroxy  derivative  (oxyproline) ;  (vi)  furaldehyde 
(p.  517);  (vii)  histidine  (iminazole-alanine),  CGH902Ng;  (viii) 
arginine,  or  8-guanino-a-amino  valeric  acid,  NH2  •  C( :  NH)  •  NH  • 
CH2.CH2.CH2.CH(NH2).C02H,  which  has  been  synthesised 
from  ornithine  (p.  465)  and  cyanamide  (p.  277);  (ix)  trypto- 
phan  (indol-alanine);  (x)  tyrosine  (p.  459). 

Of  the  diamino-acids  the  following  are  the  more  important: 
Diamino- acetic  acid  from  casein,  a8-diamino-valeric  acid  or 
ornithine,  ac-diamino-T^caproic  acid  or  lysine. 

Of  the  monamino-acids :  Glycocoll,  and  derivatives  such  as 
skatolglycocoll,  a-amino-propionic  acid  or  alanine,  a-amino- 
isobutylacetic  acid  or  leucine,  a-amino-isovaleric  acid  or  valine, 
a-amino-succinic  or  aspartic  acid,  a-amino-glutaric  or  glutamic 
acid,  phenylalanine  or  /?-phenyl-a-amino-propionic  acid,  CH2 
Ph  •  CH(NH2)  •  C02H,  a-amino-a-hydroxy-propionic  acid  or 
serine,  a-amino-a-thiolactic  acid  or  cystein,  and  the  corre- 
sponding disulphide  or  cystin,  /?-hydroxy-phenyl-a-amino-pro- 
pionic  acid. 

Certain  albumins  also  yield  carbohydrates,  more  especially 
amino-sugars,  e.g.  glucosamine,  C6Hn05«NH2  (B.  1895,  28, 
3082). 

A  simple  method  for  the  separation  and  isolation  of  many 
of  these  amino-acids  from  the  products  of  hydrolysis  is  due  to 
E.  Fischer.  He  converts  the  acids  into  esters  by  the  hydrogen- 
chloride  method,  and  then  separates  these  by  fractional  dis- 
tillation under  reduced  pressure. 

A  few  simple  proteins  yield  only  a  single  ammo-derivative; 
thus  both  salmine  and  clupeine,  obtained  respectively  from  the 
testicles  of  the  salmon  and  herring,  yield  very  little  besides 
histidine.  As  a  rule,  the  more  complex  proteins  yield  a 
considerable  number  of  amino-compounds,  the  number  of  such 
compounds  and  also  their  relative  proportions  varying  with 
the  protein. 

A  glance  at  the  list  of  above  products  indicates  that  the 
albumin  molecule  is  largely  built  up  of  aliphatic  groups. 
The  carboxylic  groups  present  in  the  hydrolytic  products 
are  probably  not  present  in  the  original  molecule,  and  it  is 
highly  probable  that  most  of  the  amino-groups  are  not  present 
as  such,  but  are  employed  in  uniting  the  various  radicals 
together,  since  only  some  10  per  cent  of  the  total  nitrogen  in 


ALBUMINS  597 

albumin  is  eliminated  as  such  on  treatment  with  nitrous  acid  ; 
in  other  words,  the  amino-group  of  one  molecule  reacts  with 
the  carboxylic  group  of  another,  yielding  compounds  with  the 
group,  •  CO'NH',  characteristic  of  acid  amides.  Emil  Fischer 
and  others  have  synthesised  complex  compounds  of  this  type 
by  the  gradual  condensation  of  amino-acids.  Although  none  of 
the  proteins  has  been  so  far  synthesised,  the  products  —  the 
polypeptides  —  exhibit  considerable  analogy  to  the  peptones. 

The  following  general  methods  are  used  for  the  synthesis 
of  polypeptides  :  — 

1.  The  chloride  of  a  halogenated  fatty  acid  is  condensed 
with  the  ester  of  an  amino-acid,  the  resulting  ester  hydrolysed, 
and  the  halogen  then  replaced  by  an  amino-group  by  means 
of  ammonia: 


Cn3.CHBr.COCl 

—  CH8-CHBr.CO.NH.CH2.C02Et 
—  CH3.CH(NHa).CO. 

Alanylglycine. 

2.  The  dipeptide  thus  obtained  can  be  converted  into  its 
acid  chloride,  and  this  condensed  with  a  molecule  of  an  ester 
of  an  amino-acid,  e.g.  glycine  ester,  yielding  the  compound 
CH3.CH(NH2).CO.NH.CH2.CO.NH.CH2.C02C2H5,  which 
on  careful  hydrolysis  yields  the  corresponding  acid  —  alanyl- 
glycylglycine  —  an  example  of  a  tripeptide.     The  operations 
can  be  repeated,  and  in  this  way  compounds  containing  18 
amino-acid  residues  have  been  synthesised,  one  of  which  has  a 
molecular  weight  1213. 

As  the  amino-acids  obtained  by  hydrolysing  natural  pro- 
teins are  optically  active,  Fischer  used  optically  active  acids 
and  esters  in  his  synthetical  operations,  the  optically  active 
acid  being  obtained  by  resolving  its  racemic  benzoyl  derivative 
by  means  of  active  bases  and  then  removing  the  benzoyl  group. 

3.  A  modification  of  the  above  synthesis  consists  in  con- 
verting an   amino-acid   into   its   acid   chloride   by  means  of 
acetyl  chloride  and  phosphorus  pentachloride,  and  then  con- 
densing this  chloride  with  a  molecule  of  an  amino-acid. 

4.  Glycylglycine  can  be  obtained  by  heating  ethylglycine 


when  the  anhydride  diketopiperazine,  NHQjj'^Q^NH,  is 

formed,  and  hydrolysing  this  with  dilute  alkali. 

A  few  polypeptides,  e.g.  tetrapeptides,  have  been  isolated 
from  the  hydrolytic  products  of  certain  proteiiw. 


598       XLIII.  ALBUMINS;  PHYSIOLOGICAL  CHEMISTRY 

Kutscher  has  shown  that  many  albumins  can  combine  to- 
gether to  give  complex  substances,  and  it  is  probable  that 
many  natural  albumins  are  complexes  formed  by  union  of 
simpler  molecules. 

(c)  The  putrefaction  of  albumins  gives  rise  not  only  to  amino- 
acids,  but  also  to  other  aromatic  and  fatty  acids  (e.g.  butyric 
acid,  phenyl-acetic  acid),  indole,  skatole,  and  cresol;  further, 
to  the  alkaloid-like  ptomaines  (the  toxines  or  poisonous  alka- 
loids produced  in  dead  bodies),  of  which  tetramethylene- 
diamine,  or  "  putrescine ",  and  pentamethylene-diamine,  or 
"  cadaverine ",  B.  19,  2585,  have  been  isolated  (cf.  p.  196). 
For  a  compilation  of  the  ptomaines,  see  Brieger,  Archiv.  f. 
patholog.  Anatomic,  115,  483. 

Albuminous  matters  undergo  change  when  acted  upon  by 
the  juices  of  the  stomach  at  a  temperature  of  30°-40°,  the 
enzyme  pepsin  converting  them  in  the  first  instance  into  anti- 
and  hemi-albumoses,  both  of  which  then  pass  into  peptone; 
trypsin,  an  enzyme  of  the  pancreas,  likewise  gives  rise  to  the 
two  above  albumoses,  but  then  transforms  the  anti-compound 
into  peptone  and  the  hemi-compound  into  leucine,  tyrosine, 
aspartic  acid  and  glutamic  acid  (the  pancreatic  digestion;  for 
details,  see  Kuhne,  B.  17,  Kef.  79).  The  peptones  are  readily 
soluble  in  water,  diffuse  quickly  through  vegetable  parchment, 
and  they  are  neither  coagulated  upon  heating  nor  by  most 
of  the  reagents  which  coagulate  albumin,  e.g.  ammonium 
sulphate,  whereas  the  albumoses  are  precipitated  by  this 
reagent.  These  reactions  indicate  that  the  albumoses  are 
intermediate  between  the  albumins  proper  and  the  simple 
decomposition  products  already  mentioned,  and  that  the 
peptones  are  intermediate  between  the  same  decomposition 
products  and  the  albumoses.  Both  albumoses  and  peptone 
possess  acidic  and  basic  properties,  and  may  be  esterified  by 
means  of  alcohol  and  hydric  chloride,  hence  they  probably 
contain  carboxylic  groups. 

The  different  albumoses,  e.g.  hetero-  and  proto-albumoses, 
must  differ  considerably  as  regards  constitution,  as  the  former 
yields  glycocoll,  much  arginine,  but  little  histidine,  and  very 
little  tyrosine  and  indole  on  hydrolysis,  whereas  the  latter 
yields  no  glycocoll,  equal  amount  of  arginine  and  histidine, 
and  much  tyrosine  and  indole. 

Other  methods  adopted  are  to  introduce  chemical  substances 
into  the  animal  system  intravenously  or  per  os,  and  then  to 
examine  in  what  form  the  compound  is  excreted  from  the 


ALBUMINS  599 

system;  as  examples,  bromobenzene  is  excreted  as  bromo- 
phenyl-mercapturic  acid,  and  various  terpene  derivatives  are 
excreted  in  combination  with  glycuronic  acid. 

When  soluble  salts  of  iron  are  allowed  to  act  upon  white  of 
egg  and  upon  peptone,  iron  albuminate  and  iron  peptonate 
are  respectively  produced,  these  being  employed  in  medicine 
as  iron  preparations  for  internal  use  under  the  names  of  liquor 
ferri  albuminati  and  peptonati. 

The  following  scheme  of  nomenclature  for  proteins  is  ac- 
cepted by  most  English-speaking  chemical  and  physiological 
societies : — 

1.  Protamines. — The   simplest  proteins,  they  include  sal- 
mine,  sturine,  &c.,  isolated  from  fish  testicles. 

2.  Histones. — These  are  somewhat  more  complex  than  the 
protamines.     They  can  be  precipitated  by  ammonia. 

3.  Albumins,  e.g.  egg  albumin,  serum  albumin  from  blood 
and  nutritive  fluids,  and  lact- albumin  from  milk.     These  are 
crystalline,  dissolve   in  water,  and  are  not   precipitated  by 
common  salt.     They  coagulate  at  70°-75°. 

4.  Globulins  are  insoluble  in  water  but  dissolve  in  dilute  salt 
solution.     They  can  be  salted  out  by  means  of  magnesium  sul- 
phate.   Examples :  Globulin  from  the  crystalline  lens  of  the  eye, 
nbrinogen  from  blood,  fibrin  from  clotted  blood,  and  myosin 
from  the  plasma  of  living  muscle,  are  globulin  derivatives. 

5.  Gluteins  are   proteins  of   vegetable   origin.      They  are 
soluble  in  alkalis,  and  are  closely  allied  to  the  globulins. 

6.  Gliadins. — Vegetable  proteins,  soluble  in  alcohol. 

7.  Phospho-proteins,  e.g.  caseinogen,  the  principal  protein 
of  milk;   casein  obtained  from  caseinogen  by  the  action  of 
rennet.     They  are  acidic  and  do  not  coagulate. 

8.  Sclero -proteins. — Mainly  insoluble  proteins,  which  form 
the  skeletal  parts  of  tissues,  e.g.  gelatin  from  cartilages,  chon- 
drin,   elastin  from  ligaments,  and  keratin  from  hoofs,   nails, 
hair,  &c.     Sponge  and  coral  contain  similar  substances. 

9.  Conjugated  proteins  consist  of  compounds  containing  a 
protein  molecule  united  to  some  other  group. 

(a)  Nucleo -proteins  are  important  constituents  of  the  cell 
nucleus,  e.g.  of  pus  cells,  blood  corpuscles,  and  yeast  cells. 
They  are  insoluble  in  water  or  acids,  but  dissolve  in  alkalis, 
and  contain  combined  phosphoric  acid.  On  hydrolysis  they 
yield  albumin  and  nucleic  acid,  and  on  further  hydrolysis 
the  nuclein  bases,  viz.  adenine,  hypoxan thine,  guanine,  and 
xanthine  (p.  292). 


600       XLIII.  ALBUMINS;  PHYSIOLOGICAL  CHEMISTRY 

Certain  varieties  of  nuclein  are  free  from  sulphur,  while 
others  contain  it;  the  latter  group  yield  tyrosine  when  de- 
composed. The  product  which  is  obtained  when  the  albumin 
of  hens'  eggs  is  coagulated  by  meta-phosphoric  acid  resembles 
nuclein. 

Nucleic  acid  may  also  be  transformed  into  nuclein  bases  by 
various  enzymes  present  in  the  different  organs  of  the  animal 
system.  Recent  work  renders  it  highly  probable  that  at  least 
three  distinct  enzymes  take  part  in  such  transformations: 
(a)  an  oxidase;  (b)  adenase,  which  transforms  adenine  into 
hypoxanthine  and  xanthine;  (c)  guanase,  which  transforms 
guanine  into  xanthine. 

(b)  Chroma-proteins  or  Haemoglobins. — Haemoglobin  is  the 
colouring  matter  of  the  red  blood  corpuscles.     It  can  be  de- 
composed into  globin  and  hsematin  (see  below).    Haemoglobin 
combines  very  readily  with  oxygen,  e.g.  in  the  lungs,  to  oxy- 
haemoglobin,  which  yields  up  its  oxygen  again,  not  only  in 
the  organism,  but  also  in  a  vacuum  and  when  exposed  to  the 
action  of  reducing  agents,  e.g.  ammonium  sulphide.    With  car- 
bon monoxide  it  combines  to  the  compound,  carbon  monoxide- 
hsemoglobin.     All  three  compounds  can  be  obtained  crystal- 
lize* in  the  cold,  and  they  possess  characteristic  absorption 
spectra.     Hsemin,  C84H3204N4FeCl,  is  obtained  in  the  form  of 
characteristic  microscopic,  reddish-brown  crystals  by  the  action 
of  glacial  acetic  acid  and  some  common  salt  upon  oxy-hsemo- 
globin;    this  is  a  delicate  test  for  the  presence  of  blood. 
Hsematin,  a  dark-brown  powder  containing  8  per  cent  of  iron, 
is  obtained  by  the  spontaneous  decomposition  of  haemoglobin, 
or  by  the  action  of  alkalis  on  hsemin,  and  contains'  OH  in 
place  of  the  Cl  atom  of  hsemin  (cf.  Piloty  and  Eppinger,  A. 
377,  341). 

(c)  Gluco-proteins. — The  mucins  yield  albumin  and  carbo- 
hydrate on  hydrolysis;  they  are  insoluble  in  water,  but  possess 
acidic  properties.     The  percentage  of  nitrogen  is  less  than  in 
the  ordinary  albumins. 

10.  Protein  derivatives,  or  the  products  of  protein  hy- 
drolysis. 

(a)  Meta-proteins. — This  includes  the  substances  previously 
known  as  alkali-albumins  and  acid-albumins,  (b)  Froteoses, 
including  albumoses,  globuloses,  and  gelatoses.  (c)  Peptones 
(cf.  p.  598).  (d)  Polypeptides  (cf.  p.  597). 


REDACTION  WITH  NASCENT  HYDROGEN  601 

XLIV.   REDUCTION 

Reduction  is  the  name  usually  given  to  a  reaction  in  which 
oxygen  is  withdrawn  from  or  hydrogen  added  to  a  compound; 
in  certain  cases  both  of  these  processes  occur.  Numerous  cases 
of  reduction  have  been  mentioned  in  the  preceding  chapters, 
as  examples: 

(C6H6)2'N20,  azoxy  -benzene,  —  *•  (C6H5)2N2,  azo-benzene  (p.  397); 
(CH3)2.CO,  acetone,  —  >  (CH3)2.CH.OH,  iso-propyl  alcohol 

(P.  72); 
nitre-benzene,      —  -  C6H6NH2,  aniline  (p.  372). 


As  the  reaction  is  so  general,  a  more  detailed  discussion  of  it 
is  given  in  this  chapter. 

In  addition  to  the  above  reactions,  viz.  withdrawal  of 
oxygen  or  addition  of  hydrogen,  the  process  previously 
referred  to  as  inverse  substitution  (p.  33)  —  the  replacement 
of  halogen  by  hydrogen,  e.g.  C2H5I  —  -  C2H6  —  is  usually  re- 
garded as  a  type  of  reduction. 

A.  Nascent  Hydrogen.  —  Of  the  numerous  methods  that  can 
be  employed  for  reduction,  one  of  the  commonest  is  by  means 
of  nascent  hydrogen,  i.e.  hydrogen  generated  in  the  presence 
of  the  substance  to  be  reduced.  The  fact  that  the  majority 
of  these  reductions  cannot  be  effected  by  means  of  ordinary 
gaseous  hydrogen,  but  can  be  readily  attained  by  the  use  of 
hydrogen  at  its  moment  of  formation,  is  used  as  an  argument 
in  favour  of  the  view  that  nascent  hydrogen  consists  of  the 
free  atoms.  As  nascent  hydrogen  can  be  produced  in  a 
variety  of  ways,  it  follows  that  reductions  by  this  method 
can  be  conducted  under  very  varying  conditions;  and  it  is  of 
extreme  importance  to  note  that  the  conditions  are  a  prime 
factor  in  determining  the  nature  of  the  product.  It  has 
already  been  pointed  out  that  the  reduction  of  nitro-benzene 
can  give  rise  to  azoxy-benzene,  azo-benzene,  phenyl-hydroxyl- 
amine,  or  aniline,  according  to  the  conditions  under  which  the 
reaction  occurs;  and  similar  phenomena  have  been  mentioned 
in  the  case  of  the  reduction  of  terephthalic  acid  (p.  468). 

Reductions  by  means  of  nascent  hydrogen  may  take  place 
in  acid,  alkaline,  or  neutral  solution,  and  this  affords  a  simple 
method  of  classification  for  these  reactions. 

(a)  Reduction  in  Acid  Solution.  —  Almost  any  combination 
of  acid  and  metal  which  gives  rise  to  nascent  hydrogen  may 
be  employed  for  this  purpose;  but  the  usual  combinations  are 


XLIV.    REDUCTION 

tin  and  hydrochloric  acid,  zinc  and  hydrochloric  acid,  zinc  and 
acetic  acid,  zinc  dust  and  acetic  acid,  iron  and  acetic  acid. 

The  usual  method  employed  in  the  laboratory  for  the 
reduction  of  iiitro-compounds  to  the  corresponding  ammo- 
compounds  (see  Aniline)  is  by  means  of  tin  and  hydrochloric 
acid.  The  metal  is  first  converted  into  stannous,  and  then 
into  stannic  chloride : 

Sn  +  2HCl  =  SnCl2  +  2H; 
SnCL  +  2HCl  =  SnCl4  +  2H; 
C6H5N02  +  6H  =  C6H5.NH2  +  2H20; 
or     C6H4(N02)2  +  12H  =  C6H4(NH2)2  +  4H2O. 

The  method  has  certain  objectionable  features  which  render 
it  unsuitable  for  use  on  the  manufacturing  scale.  Among 
these  may  be  mentioned  (a)  need  for  large  excess  of  concen- 
trated acid,  and  the  fact  that  this  acid  will  subsequently  have 
to  be  neutralized,  (b)  The  strong  acid  is  liable  to  react  with 
the  reduction  product,  yielding  halogenated  amines.  The  in- 
troduction of  the  halogen  into  the  benzene  nucleus  probably 
occurs  in  the  following  manner: — 

C6H6.N02  —  C6H6.NH-OH  —  C6H6.NHC1  ->  C1.C6H4.NH2 

(Bamberger).  Such  chlorinated  amines  are  always  liable  to  be 
formed  when  concentrated  hydrochloric  acid  is  used  in  com- 
bination with  a  metal  for  the  reduction  of  nitro-compounds. 
(c)  The  reduced  compound  often  combines  with  the  stannic 
chloride  to  form  a  double  salt,  e.g.  C6H5«NH2,  HC1,  SnCl4, 
and  certain  of  these  are  somewhat  difficult  to  decompose. 

Aliphatic  nitro-derivatives  may  also  be  reduced  to  amines 
by  this  method,  except  in  cases  where  two  nitro-groups  are 
attached  to  the  same  carbon  atom,  when  a  ketone  is  formed. 
Other  examples  are  the  conversion  of  cyclic  derivatives  into 
hydro-derivatives,  e.g.  jp-hydroxy-quinoline  to  tetrahydro-jp- 
hydroxy-quinoline,  and  of  sulphonic  chlorides,  R-S02'C1,  into 
thio-phenols,  R'SH. 

In  many  cases  tin-foil  is  stated  to  be  preferable  to  granu- 
lated tin,  as  it  exposes  a  larger  surface,  and  occasionally 
alcoholic  solutions  of  the  hydrogen  chloride  are  used  in  place 
of  aqueous.  Stannous  chloride  and  hydrochloric  acid  occa- 
sionally give  better  yields  than  tin  and  acid;  thus  nitro- 
methane  is  reduced  to  methyl-hydroxylamine,  and  the  method 
has  been  recommended  for  the  estimation  of  nitro-groups. 
An  excess  of  standard  stannous  chloride  solution  is  used,  and 


REDUCTION   WITH  NASCENT  HYDROGEN  603 

the  excess  titrated  after  the  reduction  is  complete,  each  nitro- 
group  requiring  3  gram  molecules  of  stannous  chloride. 

Stannous  chloride  is  sometimes  used  without  the  addition 
of  free  acid;  thus  Witt,  by  reducing  amino-azo-benzene  with 
alcoholic  stannous  chloride,  obtained  aniline  and  ^-phenylene- 
diamine  : 

CcH5-N:N.C6H4.NH2-f  4H  =  C6H5-NH2  +  NH2.C6H4.NH2. 

(Compare  also  Jacobson,  A.  1895,  287,  100.) 

Most  of  the  objections  referred  to  in  connection  with  the 
reduction  of  nitre-derivatives  by  means  of  tin  and  hydro- 
chloric acid  may  be  avoided  by  using  iron  and  acetic  acid  or 
dilute  hydrochloric  acid.  This  method  is  usually  adopted  on 
the  manufacturing  scale,  as  only  a  small  amount  of  acid,  some 
one-fortieth  of  that  indicated  by  the  equation, 

C6H5N02  +  3Fe  +  6HC1  =  C6H5.NH2  +  3FeCl2  +  2H2O, 

is  required.  The  reason  for  this  may  be  that  the  ferrous 
chloride  reacts  with  the  aniline  and  water,  yielding  ferrous 
hydroxide  and  aniline  hydrochloride  : 

2C6H6NH2-f  2H20  =  Fe(OH)2  +  2C6H5N 


The  hydrochloride  then  reacts  with  more  iron,  producing 
ferrous  chloride  and  nascent  hydrogen,  which  can  reduce 
more  of  the  nitro-compound. 

The  iron  method  possesses  further  advantages,  as  r  the 
reduction  can  be  regulated  much  more  readily  than  in  the 
case  of  tin  and  acid.  Thus  ^?-nitro-acetanilide  reduced  by 
the  iron  method  gives  the  corresponding  ammo-compound, 
NH2.C6H4.NH.CO-CH3,  whereas  with  tin  and  hydrochloric 
acid  hydrolysis  and  reduction  both  occur,  and  the  product  is 
jp-phenylene-diamine. 

Iron  and  acid  may  also  be  employed  for  the  reduction  of 
aromatic  polynitro-compounds  to  amino-nitro-derivatives  : 

C6H4(N02)2 


but  such  a  reduction  is  almost  impossible  with  tin  and  acid. 

Zinc,  as  granulated  zinc,  or  more  frequently  as  zinc  dust,  is 
also  used  in  conjunction  with  acids,  usually  hydrochloric  or 
acetic.  When  concentrated  hydrochloric  is  employed,  chlorine 
is  apt  to  enter  the  benzene  ring  (cf.  p.  602);  with  glacial  acetic 
acid  (Kra/ts,  B.  1883,  16,  1715)  acetyl  derivatives  are  formed 
occasionally  instead  of  the  simple  reduction  products.  For 


604  3tLlV.   REDACTION 

example,  when  aldehydes  are  reduced,  alkyl  acetates  and  not 
alcohols  are  formed: 


K-CHO  +  2H  +  CH3.C02H  =  R-CH^O-CO-CH, 

and  when  nitro-derivatives  are  reduced,  acetylated  amines  are 
obtained.  Although  aliphatic  ketones  cannot  be  reduced  by 
this  method,  all  ketones  containing  one  or  two  benzene  nuclei 
directly  attached  to  the  carbonyl  group  are  readily  reduced  to 
pinacones  (p.  191).  Hydroxy-derivatives  of  anthraquinone 
may  also  be  reduced  in  a  similar  manner,  one  or  more  of  the 
hydroxy-  groups  being  replaced  by  hydrogen,  and  aliphatic 
nitro-derivatives,  such  as  nitro-guanidine,  NH:C(NH2)»NH- 
N02,  may  be  reduced  to  the  corresponding  amino-compounds. 
A  transformation  occasionally  effected  by  means  of  zinc  dust 
and  glacial  acetic  acid  is  the  removal  of  two  atoms  of  halogen 
and  the  conversion  of  a  saturated  compound  into  an  olefine, 
e.g.  tetramethyl-ethylene  dibromide  into  tetramethyl-ethylene  : 
CMe2Br-CMe2Br  +  2H  =  2HBr  -f  CMe2:CMe2. 


All  peroxides  (p.  181)  are  readily  reduced  by  this  method, 
e.g.  diethyl-peroxide,  Et202,  to  ethyl  alcohol  (or  ethyl  acetate). 

Dilute  acetic  acid  is  frequently  used  with  zinc  dust.  This 
is  the  usual  method  adopted  for  the  reduction  of  osones  to 
ketoses  (Fischer)  (p.  304): 

K.CO.CHO  +  2H  =  B.CO.CH2.OH. 

It  is  also  extremely  useful  in  the  preparation  of  hydrazines 
from  nitrosamines  and  nitramines,  e.g.  Fischer  (A.  1886,  236, 
198)  obtained  methyl-phenyl-hydrazine,  NPhMe»NH2,  by  the 
reduction  of  methyl-phenyl-nitrosamine,  NPhMe-NO.  Other 
reducing  agents,  e.g.  metal  and  concentrated  hydrochloric 
acid,  stannous  chloride,  zinc  dust  and  alkali,  are  all  liable  to 
carry  the  reduction  a  stage  further  and  yield  a  mixture  of 
ammonia  and  amine: 

NPhMe.NH2  +  2H  =  NHPhMe  +  NH3. 

An  extremely  interesting  example  of  the  influence  of  the 
reducing  agent  and  the  method  of  reduction  on  the  nature 
of  the  final  product  is  met  with  in  the  case  of  nitro-benzyl- 
phenyl-nitrosamine,  N02  •  C6H4  •  CH2  •  NPh  •  NO.  With  tin 
and  hydrochloric  acid  it  yields  phenyl-indazole, 

M 

>NPh; 


c«H<L> 


REDUCTION  WITH  NASCENT  HYDROGEN  605 

with  sodium  amalgam  in  alkaline  solution,  o-amino-benzyl- 
aniline,  NH2  -  C6H4  •  CH2  •  NHPh,  and  ammonia;  and  with  zinc 
dust  and  glacial  acetic  acid,  o-amino-benzyl-phenyl-hydrazine, 
NH2.C6H4.CH2.NPh.NH2.  (Busch,  B.  1894,  27,  2899.) 

With  zinc  dust  and  dilute  sulphuric  acid  the  reaction  is 
somewhat  slower  than  with  acetic  acid;  with  these  reagents 
sulphonic  chlorides  may  be  transformed  into  thio-phenols,  or 
the  reaction  may  proceed  a  stage  further  and  the  sulphur  be 
completely  removed. 

Zinc  dust  and  concentrated  sulphuric  acid  are  occasionally  used 
for  the  reduction  of  nitro-compounds,  and  in  all  cases  the  pro- 
duct is  an  amino-hydroxy-  and  not  a  simple  amino-derivative  : 
C6H6.N02  —  jE>-NH2.C6H4.OH; 

-*  NH2.C6H3(OH).C02H. 


Lassar-Cohn  attributes  this  to  the  oxidizing  action  of  the 
concentrated  sulphuric  acid,  whereas  it  is  probable  that 
reduction  to  a  phenyl-hydroxylamine  first  occurs;  and  this, 
in  the  presence  of  the  concentrated  acid,  undergoes  intra- 
molecular rearrangement,  yielding  the  amino-phenol  (cf.p.397): 
C6H5.N02  —  C6H6.NH.OH  —  OH.C6H4.NH2. 

When  zinc  or  zinc  dust  and  any  acid  are  added  to  the 
nitrate  of  an  aromatic  amine,  a  diazonium  salt  is  formed: 
C6Ha.NH2,HN03-f  Zn-f  3HC1  =  ZnCl2  -f  C6H5N2C1  -f  3H20. 

Sodium  amalgam  is  sometimes  used  as  a  reducing  agent  in 
the  presence  of  acid;  thus  with  acetic  acid  it  is  used  for  the 
reduction  of  hydrazones  to  primary  amines  : 


Reductions  by  means  of  sodium  amalgam  and  dilute  sulphuric 
acid  have  been  largely  used  by  E.  Fischer  in  his  synthetical 
work  on  the  sugars,  since  the  lactones  of  hydroxy-acids  when 
reduced  in  this  way  at  0°  yield  aldoses  (pp.  304,  305)  : 

X.CH.CH(OH).CH(OH).CO-*X.CH(OH).CH(OH).CH(OH).CH:0. 

I  _  0  _  I 

The  same  reducing  agents  convert  phloroglucinol,  s-C6H3(OH)8, 
into  its  hexahydro-derivative. 

A  very  common  acid  reducing  agent  is  hydriodic  acid,  its 
reducing  action  being  attributed  to  the  decomposition  of  the 
hydrogen  iodide  into  iodine  and  nascent  hydrogen  at  moderate 
temperatures.  The  method  was  first  introduced  by  Berthelot, 


606  XLIV.    REDUCTION 

who,  in  his  earlier  experiments,  used  the  acid  alone;  but  when 
he  found  that  the  liberated  iodine  interfered  with  the  reduc- 
tion by  giving  rise  to  iodo-derivatives  or  by  oxidizing,  he 
added  red  phosphorus  or  sometimes  phosphonium  iodide. 
The  function  of  the  phosphorus  is  to  combine  with  the  iodine 
immediately  it  is  liberated  from  the  hydrogen  iodide,  and 
thus  form  phosphorus  tri-iodide,  which  is  then  decomposed  by 
the  water  present,  yielding  hydrogen  iodide  and  phosphorous 
acid.  Phosphonium  iodide  is  often  formed  as  a  by-product  in 
these  reductions.  It  has  been  shown  that  with  hydriodic  acid 
alone  practically  all  oxygen  compounds  are  reduced  to  satu- 
rated hydrocarbons  at  a  temperature  of  275°,  the  reduction 
being  conducted  in  sealed  cubes,  e.g.  glycerol  yields  propane. 
Amines  are  also  transformed  into  paraffins,  e.g.  methylamine 
yields  methane. 

When  hydriodic  acid  and  phosphorus  are  used,  the  reduction 
can  either  take  place  in  open  vessels,  e.g.  a  flask  with  reflux 
condenser,  or  in  sealed  tubes  if  a  higher  temperature  is  required 
As  examples  of  the  former  we  have  the  following : — CHI3  — » 
CHJL;  anthraquinone  — *  dihydro-anthracene ;  benzilic  acid, 
OH.CPh2.G02H  — diphenyl-acetic  acid,  CHPtyC02H;  tri- 
hydroxy-glutaric  acid,  COJ! .  [CH . OH]3 .  C02H  —  glutaric 
acid;  mixed  ketones,  e.g.  C6H5 •  CO •  CH3  — *•  hydrocarbons. 

As  examples  of  the  latter  we  have  the  conversion  of  fatty 
acids,  from  C8Hir«C02H  upwards,  into  paraffin-hydrocarbons, 
the  reduction  of  anthracene  to  hydro-anthracenes,  and  of 
hydroxy  -  hexamethylene  carboxylic  acid,  OH  •  C6H10  •  C02H, 
to  hexahydro-benzoic  acid,  C6Hn«C02H. 

It  is  interesting  to  note  that  hydriodic  acid  is  not  a  good 
reducing  agent  for  nitre-compounds ;  as  a  rule  it  leaves  the 
nitro- group  intact,  e.g.  nitro  -  benzene  -  sulphonic  chloride, 
N02.C6H4.S02C1,  yields  first  N02.96H4.SO.SO.C6H4.N02, 
and  ultimately  m-dinitro-diphenyl-disulphide,  N02-C6H4«S« 
S.C6H4.N02. 

(b)  Nascent  Hydrogen  in  Alkaline  Solution. — There  are 
various  methods  of  reducing  with  nascent  hydrogen  in  al- 
kaline solution;  one  of  the  commonest  is  the  addition  of 
metallic  sodium,  in  the  form  of  wire  or  thin  strips,  to  boiling 
ethyl  alcohol;  as  a  rule  it  is  necessary  to  use  absolute  alcohol* 
as  the  presence  of  water  diminishes  the  yields.  As  examples, 
we  have  the  reduction  of  nitriles  to  primary  amines,  R»CN 
— *R.CH2-NH2  (p.  106),  of  esters  to  alcohols  (p.  72),  of  naph- 
thalene to  dihydro-naphthalene,  of  pyridine  to  piperidine  (p.  537), 


REDUCTION  WITH  NASCENT  HYDROGEN  607 

although  quinoline  is  not  so  readily  converted  by  this  process 
into  tetrahydro-quinoline,  and  lastly,  of  various  benzene  deriva- 
tives, e.g.  w-hydroxy- benzoic  acids  into  corresponding  hexa- 
hydro-derivatives,  i.e.  derivatives  of  hexamethylene.  When 
a  higher  temperature  is  required  than  can  be  attained  with 
ethyl  alcohol,  boiling  amyl  alcohol  is  used  (Bamberger).  By 
this  method  naphthalene  and  its  derivatives  may  be  converted 
into  their  tetrahydro-compounds,  e.g.  the  naphthols,  C10H7'OH, 
into  tetrahydro-naphthols,  C10Hn  •  OH. 

It  is  interesting  to  note  that  the  chief  reduction  product 
obtained  from  a-naphthylamine  is  ar-tetrahydro-a-naphthyla- 
mine  (I),  and  from  /3-naphthylamine  a  mixture  of  ar-  and  ac- 
tetrahydro-derivatives  (II  and  III): 

H2    NH2  H2    H 


Similarly  phenanthrene  is  reduced  to  its  tetrahydro-deriva- 
tive,  anthracene  to  its  dihydro-compound,  and  the  benzene 
carboxylic  acids  to  di-,  tetra-,  or  hexahydro-derivatives,  accord- 
ing to  the  temperature  and  other  conditions  of  reduction 
(cf.  p.  467);  with  sodium  and  boiling  amyl  alcohol,  benzoic 
acid  yields  mainly  C6Hn«C02H.  In  a  few  cases,  when  sub- 
stituted benzoic  acids  are  reduced  by  this  method,  a  rupture 
of  the  ring  occurs  and  an  aliphatic  acid  is  formed.  One  of  the 
best-known  examples  is  the  reduction  of  salicylic  acid  to  pimelic 
acid  (p.  344);  in  this  case  it  may  be  assumed  that  a  tetra- 
hydro-salicylic  acid  is  first  formed,  and  that  by  the  addition 
of  the  elements  of  water  this  is  converted  into  pimelic  acid  : 


<xCH2.C(C02HKG  OH 
\CH2  •  CH2  -  -/^  C 


Although  aniline  cannot  be  converted  into  its  hydro-deriva- 
tives by  this  method,  aniline-o-sulphonic  acid  yields  a  hexa- 
hydro-derivative.  In  place  of  alcohol  moist  ether  is  sometimes 
used  in  conjunction  with  sodium.  This  is  generally  accom- 
plished by  adding  the  metal  to  ether  floating  on  water,  or 
better,  on  a  solution  of  sodic  bicarbonate.  Dibenzyl  ketone 
can  thus  be  reduced  to  dibenzyl-carbinol,  mesityl  oxide  to 


608  XLIV.   REDUCTION 

methyl-isobutyl-carbinol,  and  acid  chlorides,  E«COC1,  to  the 
corresponding  alcohols,  B«CH2«OH. 

Sodium  amalgam  may  be  used  in  place  of  sodium  itself,  as 
a  rule  in  combination  with  water;  the  amalgam  is  added 
gradually  and  the  mixture  kept  agitated,  and  a  small  amount 
of  alcohol  is  added,  if  necessary,  to  prevent  frothing.  By  this 
method,  benzene  and  its  derivatives  may  be  reduced  to  di-  and 
tetrahydro-compounds.  Many  olefine  derivatives  are  reduced 
to  saturated  compounds,  e.g.  cinnamic  acid,  CgH5«CH:CH' 
C02H,  to  phenyl-propionic  acid,  C6H5.CH2.CH2.C02H,  and 
ketones  to  secondary  alcohols.  Alcohol  is  occasionally  a  better 
medium  than  water,  and  by  this  method  azo-  may  be  reduced 
to  hydrazo-compounds  (p.  395),  and  benzaldehyde  and  its 
substituted  derivatives  into  benzyl  alcohols. 

In  many  instances  the  alkali  formed  by  the  action  of  the 
metal  on  water  or  alcohol  has  a  deleterious  action  on  the  pro- 
ducts of  reduction,  and  it  becomes  necessary  to  neutralize  the 
alkali  as  far  as  possible.  This  may  be  effected  by  the  occasional 
addition  of  mineral  acid,  but  is  most  readily  accomplished  by 
Aschan's  method  of  leading  carbon  dioxide  through  the  liquid 
as  the  reduction  proceeds,  and  in  this  way  converting  the 
sodium  hydroxide  into  bicarbonate  as  fast  as  formed.  It  is 
the  method  often  used  in  the  reduction  of  phthalic  acids,  &c., 
and  may  also  be  employed  for  converting  naphthalene  and 
resorcinol  into  their  dihydro-derivatives,  and  benzoic  acid  into 

Zinc  and  alkali  are  often  used  to  reduce  aromatic  ketones 
to  secondary  alcohols,  e.g.  (CgH^CO  -*  (C6H5)2CH.OH; 
whereas  when  zinc  and  acetic  acid  are  used,  the  corresponding 
pinacpnes,  (C6H5)2C(OH)  •  C(OH)(C6H5)2,  are  formed.  Alkali, 
especially  sodic  hydroxide,  may  be  used  with  zinc  dust;  the 
usual  method  being  to  keep  the  alkali  and  substance  well 
stirred,  and  to  add  the  zinc  dust  gradually.  As  examples  we 
have:  Anthraquinone  — -  anthranol ;  fatty  diazo-compounds  — * 
hydrazo-compounds;  o - nitraniline  — *•  o-phenylene-diamine. 
Further  examples  are  the  dehalogenating  of  aromatic  compounds 
and  the  preparation  of  azoxy-  and  azo-compounds  (p.  397). 

(c)  Nascent  Hydrogen  in  Neutral  Solution.— Many  reduc- 
tions take  place  most  readily  in  the  absence  of  free  acid  or  free 
alkali,  and  may  be  effected  by  the  following  reagents : — (i)  Zinc 
filings  or  granulated  zinc  and  alcohol,  e.g.  /?-bromo-allo-cinnamic 
acid  — *  allo-cinnamic  acid  (p.  454);  (ii)  Gladstone-Tribe  couple, 
in  the  reduction  of  alkyl  haloids  to  paraffins  (p.  33);  (iii)  mix- 


REDUCTION   WITH   METALS  609 

ture  of  zinc  and  iron,  in  the  presence  of  certain  metallic  salts, 
e.g.  acetone  —  *•  isopropyl  alcohol;  (iv)  zinc  dust  and  water  (or 
alcohol),  which  may  be  used  for  reducing  azo-dyes  to  mixtures 
of  amines,  e.g.  chrysoidine,  NPhiN'CgH^NHg)^  to  aniline 
and  triamino-benzene,  and  also  for  reducing  aromatic  nitro- 
compounds  to  the  corresponding  hydroxylamines,  e.g.  C6H6» 
N02  —  »•  C6H5-NH*OH,  a  reaction  which  proceeds  extremely 
readily  in  the  presence  of  ammonic  chloride  solution.  The 
same  reagents  are  extremely  useful  in  converting  sulphonic 
chlorides  into  sulphinic  acids,  C6H5'S02C1  —  *•  C6H5-S02H. 
(v)  Aluminium  amalgam  (Cohen  and  Ormandy,  B.  A.  Eeport,  1889, 
550)  is  also  a  useful  neutral  reducing  agent  in  the  presence  of 
water;  by  this  method  nitro-derivatives  are  readily  transformed 
into  hydroxylamines,  and  ketones  to  secondary  alcohols. 

B.  Among  other  chemical  methods  we  may  mention  heating 
with  metals.  Thus  azo-benzene  is  formed  when  azoxy-benzene 
is  heated  with  metallic  iron,  anthracene  when  alizarin  is  heated 
with  zinc  dust,  and  pyrrole  when  succinimide  is  heated  with 
the  same  reagent.  In  all  these  cases  the  metal  abstracts 
oxygen  and  is  converted  into  an  oxide.  It  is  a  method  fre- 
quently adopted  when  dealing  with  unknown  complex  sub- 
stances and  it  is  desired  to  know  from  what  simpler  compounds 
they  are  derived. 

Alcohol  alone,  as  in  the  conversion  of  diazonium  salts  into 
hydrocarbons  : 

H  =  C6H6  +  N2  +  HC1  +  CH3.CHO 


(p.  387). 

Sodium  ethoxide,  or  often  alcoholic  potash,  for  the  reduction 
of  nitro-compounds  to  azoxy-  or  azo-compounds  (De  Bruyn), 
and  also  for  reduction  of  deoxy-benzoin  and  other  aromatic 
ketones  to  secondary  alcohols,  e.g.  hydroxy-dibenzyl  : 
C6H6.CO-CH2.C6H5  ->  C6H6.CH(OH).CH2.C6H6 

(J.  C.  S.  1895,  604). 

Sodium  stannite,  obtained  by  adding  an.  excess  of  sodium 
hydroxide  to  stannous  chloride,  is  employed  for  preparing 
azo-compounds  from  nitrated  hydrocarbons,  for  the  reduction 
of  diazonium  salts  to  hydrocarbons,  e.g.  benzene  from  benzene 
diazonium  chloride.  An  interesting  reduction  is  the  conversion 
of  jMiitro-benzyl  chloride  into  dinitro-dibenzyl  : 

2N02.C6H4.CH2C1  ->  N02.C6H4.CH2.CH2.C6H4.N02) 
as  the  nitro-groups  are  left  intact. 

(B480)  2Q 


610  XUV.   REDUCTION 

Hydrogen  sulphide,  or  more  frequently  ammonium  sulphide, 
in  alcoholic  solution  (Cohen  and  M'Candlish,  J.  C.  S.  1905, 
1257),  is  made  use  of  for  the  reduction  of  nitro-  and  nitroso- 
derivatives  to  amines,  and  is  especially  useful  when  several 
nitro-groups  are  present  and  it  is  required  to  reduce  only  one, 
e.g.  0^H4(N(X)a  ->  m-N02.C6H4.NH2,  C6H2Me(N02)3  _* 
NH2»C6H2Me(N02)2,  &c.;  also  0-nitro-cinnamic  acid  — *  a- 
hydroxy-quinoline  or  carbostyril  (p.  546).  In  many  cases 
sulphur-derivatives  are  formed  instead  of  simpler  reduction 
products,  especially  with  ketones  or  aldehydes. 

Sulphurous  acid  is  used  in  reducing  quinones  to  quinols,  e.g. : 

C6H402  +  H2S03  +  H20  =  C6H4(OH)2  +  H2S04 ; 

and  sodium  hyposulphite,  Na2S204,  is  an  extremely  useful 
reagent  for  preparing  leuco-compounds  from  dyes. 

C.  Catalytic  Reduction,  or  reduction  by  means  of  hydro- 
gen in  presence  of  finely-divided  metals.  The  catalytic  action 
of  finely-divided  substances,  especially  platinum  black,  in  the 
combination  of  sulphur  dioxide  and  oxygen,  or  hydrogen  and 
oxygen,  or  in  the  decomposition  of  hydrogen  peroxide,  is 
well  known.  In  a  similar  manner,  numerous  carbon  com- 
pounds, when  mixed  with  excess  of  gaseous  hydrogen  and 
passed  over  a  layer  of  platinum  black  at  a  moderate  tem- 
perature, undergo  complete  reduction. 

The  action  of  other  metals  in  a  fine  state  of  division  has 
been  investigated  in  recent  years  (1897-1911)  by  Sabatier  and 
Senderens.  They  find  that  nickel,  cobalt,  copper,  and  iron  can 
act  in  somewhat  the  same  manner  as  platinum  black,  and  that 
of  these  nickel  is  the  most  efficient.  It  is  necessary  that  the 
metal  shall  be  in  an  extremely  fine  state  of  division,  and  this 
is  accomplished  by  reducing  the  metallic  oxide  in  a  current 
of  hydrogen  at  a  temperature  of  about  300°.  The  substance 
to  be  reduced  is  usually  vaporized,  mixed  with  excess  of 
hydrogen,  and  passed  over  the  metal  heated  to  a  temperature 
which  varies  somewhat  with  the  different  substances,  but 
usually  lies  between  160°  and  250°.  A  few  grams  of  the 
metal  are  usually  sufficient,  and  it  retains  its  activity  for  a 
long  time.  The  finely -divided  metal  appears  to  transform 
the  hydrogen  into  an  active  condition  comparable  with  what 
is  usually  termed  the  nascent  state. 

Of  the  numerous  reductions  which  have  been  accomplished 
by  this   process,   we  may  mention  the  following: — Carbon  ' 
monoxide  at  200°  and  carbon  dioxide  at  300°  are  reduced  to 


CATALYTIC  REDUCTION  611 

methane  and  water.  Ethylene,  propylene,  /?-hexene,  a-octene, 
&c.,  are  quantitatively  reduced  to  the  corresponding  paraffins. 
Acetylene  at  150°  and  o-heptine  at  170°  yield  ethane  and 
heptane  respectively.  Aromatic  hydrocarbons,  e.g.  benzene, 
toluene,  xylene,  cymene,  at  180°  yield  their  hexahydro-deriva- 
tives.  Ethyl-benzene  reacts  in  a  somewhat  curious  manner; 
it  appears  to  be  first  reduced  to  its  hexahydro-derivative, 
CgHn'CgHg,  but  this  is  partially  reduced  to  CJLj-CHg  and 
CH4.  Similarly  phenyl-  acetylene,  C6H5«C:CH,  yields  a 
mixture  of  ethyl  -  cyclohexane,  methyl  -  cyclohexane,  and 
methane.  The  terpenes  —  limonene,  sylvestrene,  terpinene, 
menthene  —  all  yield  ^-methyl-isopropyl-cyclohexane.  Pinene 
yields  a  dihydro-derivative  and  naphthalene  a  tetrahydro- 
compound,  and  this  with  more  hydrogen,  dekahydro  -  naph- 
thalene, C10H18  (Leroux). 

.  Aliphatic  nitriles  at  180°-200°  yield  primary  amines,  and 
finally  secondary  and  tertiary  amines  and  ammonia: 

E-ClSr  -*  K.CH2-NH2;  2K-CH2.NH2  —  *  ( 


Aromatic  nitriles  yield  ammonia  and  an  aromatic  hydro 
carbon  :          c6H6CN  +  3H2  =  C6H6.CH3  +  NH3. 

Aromatic  chloro-derivatives  are  readily  dehalogenized  at 
temperatures  above  270°  : 

C6H6C1  —  C6H6, 

and  similarly  for  polychloro-derivatives.    The  presence  of  CHg, 
OH,  and  NH2  groups  appear  to  facilitate  reduction  : 

C1.C6H4.N02  —  C6H6.NH2,HC1. 

Aliphatic  nitro-compounds  at  150°-  180°  yield  the  corre- 
sponding primary  amines,  but  at  higher  temperatures  paraffins 
and  ammonia.  Aromatic  nitro-compounds  are  best  reduced 
in  presence  of  copper  at  300°-400°;  in  this  manner  nitro- 
benzene yields  aniline  and  a-nitro-  naphthalene  a-naphthyl- 
amine;  whereas,  when  nickel  is  used,  a-nitro  -naphthalene 
yields  ammonia  and  tetrahydro-naphthalene. 

Phenol,  o-cresol,  thymol,  and  carvacrol  at  170°-  180°  are 
reduced  to  their  hexahydro-derivatives,  as  are  also  methyl- 
and  ethyl-anilines.  Aniline  at  190°  also  yields  its  hexahydro- 
derivative,  cyclohexylamine,  C-Hn  •  NH2,  but  at  the  same 
time  dicyclohexylamine,  (C6Hn)2NH,  and  cyclohexyl-aniline, 
are  produced. 


612  XLIV.    REDUCTION 

At  moderate  temperatures  (130°-160°)  polyhydric  phenols 
yield  corresponding  hexahydro-derivatives. 

Alcohols  are  formed  by  the  reduction  of  aldehydes  and 
ketones  at  temperatures  slightly  above  their  boiling-points, 
e.g.: 

(C2H5)2CO  -*  (C2H6)2CH.OH. 

Olefine  derivatives  are  readily  transformed  into  the  corre- 
sponding saturated  compounds  at  moderate  temperatures,  and 
compounds  of  the  aromatic  series,  e.g.  cinnamic  acid,  can  be 
reduced  to  saturated  compounds  without  the  benzene  nucleus 
being  affected.  Unsaturated  ketones,  e.g.  mesityl  oxide  and 
phorone,  can  be  reduced  to  the  corresponding  saturated 
ketones.  Diketones  yield  various  products:  thus  diacetyl  at 
140°-150°  yields  a  mixture  of  hydroxyketone  and  glycol; 
acetonylacetone  yields  the  anhydride  of  the  corresponding 
glycol;  benzil,  benzoin,  and  benzoylacetone  yield  the  corre- 
sponding hydrocarbons.  Lsevulic  acid  yields  valerolactone, 
quinones  yield  quinols,  and  carbylamines,  alkyl  isocyanates, 
and  oximes  yield  mixtures  of  amines,  mainly  secondary. 
(Sabatier  and  Senderens,  Annales,  1905  [viii],  4,  319;  Sabatier 
and  Maihle,  ibid.  1909,  16,  70;  Sabatier,  B.  1911,  44,  1984.) 

Recent  experiments  have  shown  that  finely  divided  palla- 
dium or  platinum  can  bring  about  the  reduction  of  various 
carbon  compounds  at  moderately  low  temperatures.  Paal  and 
Gerum  (B.  1907,  40,  2209)  show  that  when  hydrogen  is  passed 
through  an  alcoholic  solution  of  nitrobenzene  mixed  with  a 
small  amount  of  colloidal  platinum,  a  50-per-cent  yield  of 
aniline  can  be  obtained  at  temperatures  between  65°  and  85°. 
They  also  show  (B.  1908,  41,  2273;  1909,  42,  1553,  2244, 
3930)  that  unsaturated  acids  and  esters,  e.g.  fumaric  acid, 
maleic  acid,  cinnamic  acid,  and  methyl  cinnamate  can  be 
reduced  to  their  saturated  analogues  by  passing  hydrogen 
into  their  alcoholic  solutions  at  the  ordinary  temperature, 
provided  small  amounte  of  colloidal  platinum  or  palladium, 
or  even  of  palladium  black,  are  present.  They  have  used  the 
method  for  converting  unsaturated  oils  (oleic  acid  derivatives) 
into  saturated  glycerides.  (Cf.  also  Willstatter  and  Mayer, 
ibid.  1475,  2199.)  The  most  effective  reagent  appears  to  be 
colloidal  palladium.  On  this  reaction  FoJcin  (Abs.  1908,  ii,  637) 
suggests  a  method  for  determining  the  "  hydrogen  value  "  of 
unsaturated  acids  by  ascertaining  the  volume  hydrogen 
absorbed  by  an  alcoholic  solution  of  a  known  weight  of  the 


CATALYTIC  REDUCTION  613 

unsaturated  compound  when  well  shaken  with  the  gas  in  the 
presence  of  molecular  platinum.  A.  Skita  prepares  the  col- 
loidal palladium  by  the  addition  of  gummi  arabicum  to  a 
slightly  acidified  solution  of  palladous  chloride,  and  shows 
that  unsaturated  ketones  are  converted  into  saturated,  that 
citral  yields  citronellal  and  citronellol,  and  that  many  alka- 
loids take  up  hydrogen  (B.  42,  1627;  44,  2862). 

The  reduction  proceeds  most  rapidly  when  the  hydrogen 
is  under  an  increased  pressure  of  0-25  to  1  atmosphere. 
(Skita  and  Hitter,  B.  1910,  43,  3393.)  By  this  method  un- 
saturated ketones  are  reduced  to  saturated  without  the 
carbonyl  group  being  affected: — d-pulegone  — *  e£-menthone, 
mesityl  oxide  — »•  methyl -isobutyl  ketone.  An  exception  is 
met  with  in  phorone  (p.  137),  which  yields  di-isobutyl  car- 
binol.  If,  however,  a  smaller  pressure  is  used  the  reduction 
stops  at  the  formation  of  the  saturated  ketone,  valerone. 
Similarly  in  the  other  cases,  if  the  pressure  of  the  hydrogen 
is  increased,  a  saturated  secondary  alcohol  is  obtained.  Cyclic 
ketones  and  aromatic  aldehydes  can  be  reduced  to  alcohols, 
using  a  pressure  of  5  atmospheres.  Skita  (B.  44,  2862,  and 
Chem.  Zeit.,  1911,  35,  1098)  shows  that  in  many  cases  a  solu- 
tion of  palladous  chloride  in  hydrochloric  acid  can  be  used, 
instead  of  the  colloidal  metal,  with  equally  good  results. 

Ipatie/(B.  34,  596,  3579;  35,  1047,  1057;  36,  1990,  2003, 
2014,  2016;  37,  2961,  2986;  40,  1270,  1281,  1827;  41,  991, 
993,  996,  1001;  42,  2089,  2092,  2097)  has  studied  the  re- 
duction by  numerous  carbon  compounds  with  hydrogen  under 
pressures  of  100-120  atmospheres  in  the  presence  of  various 
catalysers. 

A  special  iron  or  gun-metal  bomb  has  been  constructed  for 
this  purpose,  and  can  be  heated  to  the  required  temperature 
in  an  electric  furnace.  Of  the  catalytic  agents  investigated, 
namely,  iron,  nickel,  copper,  aluminium,  nickelous  and  nickelic 
oxide  (Ni203),  the  last  named  was  found  to  be  the  most  effec- 
tive, and  only  2-3  grm.  were  required  for  20-30  grm,  of  the 
substance  to  be  reduced.  The  oxide  may  be  used  a  second 
time,  but  afterwards  is  less  active;  analysis  of  the  recovered 
oxide  indicates  that  only  a  comparatively  small  amount  of 
reduction  to  metallic  nickel  has  taken  place.  In  most  cases 
the  best  temperature  is  230°-260°.  Under  such  conditions, 
acetone  yields  pure  isopropyl  -  alcohol ;  phenol,  hexahydro- 
phenol;  diphenyl,  dicyclohexyl ;  naphthalene,  tetra-  or  deka- 
hydronaphthalene;  dibenzyl,  dicyclohexylethane;  a-  and  p- 


614  XLIV.   REDUCTION 

naphthols,  o-  and  /2-dekahydronaphthols,  and  similarly  for 
sodium  /3-naphthioate;  benzophenone,  diphenylmethane;  so- 
dium benzoate,  sodium  hexahydrobenzoate  (60  per  cent  yield 
of  pure  acid);  aniline,  hexahydroaniline  (50  per  cent  yield); 
diphenylamine,  dicyclohexylamine  (C6Hn)2NH;  quinoline,  de- 
kahydroquinoline;  anthracene,  perhydroanthracene,  C14H24; 
phenanthrene,  perhydrophenanthrene,  C14H24;  acenaphthene, 
dekahydroacenaphthene.  In  the  last-mentioned  reactions  it 
is  necessary  to  repeat  the  reduction  three  times  in  order  to 
obtain  the  perhydro  -  derivatives.  Olefines  are  reduced  to 
paraffin  derivatives. 

It  is  claimed  that  this  method  is  much  better  and  yields 
purer  products  than  Sabatier  and  Seiiderens'  method  of  reducing 
with  hydrogen  at  atmospheric  pressure  and  in  the  presence  of 
finely  divided  nickel. 

D.  Electrolytic  Reduction. — Within  recent  years,  numerous 
reductions  have  been  effected  by  electrolytic  methods.  The 
basis  of  all  these  methods  is  the  fact  that  when  an  electric 
current  is  passed  through  an  aqueous  solution  of  an  acid  or 
an  alkali,  using  metal  electrodes,  hydrogen  in  the  nascent 
state  is  produced  at  the  cathode  or  negative  terminal.  The 
actual  products  formed  are  dependent  not  merely  on  the 
substances  reduced,  but  also  upon  the  conditions,  among  the 
most  important  of  which  we  may  mention:  (a)  nature  and 
concentration  of  solvent,  e.g.  dilute  or  concentrated  acid, 
alkaline  or  neutral  solvent;  (b)  strength  of  current  or  the 
current  density,  i.e.  the  intensity  of  the  current  per  square 
decimetre  of  electrode;  (c)  the  materials  of  which  the  elec- 
trodes are  made,  due  to  the  difference  of  potential  at  which 
the  hydrogen  ions  are  discharged  (as  a  rule  platinum,  mercury 
or  lead  electrodes  are  used);  and  (d)  the  temperature. 

The  method  has  been  mainly  used  for  the  reduction  of  aro- 
matic nitro-compounds,  of  ketones,  and  of  unsaturated  acids. 

In  many  cases  the  reduction  is  carried  out  in  a  double  cell  pro- 
vided with  a  diaphragm,  (a)  The  cathode  solution  is  placed  in 
an  ordinary  unglazed  porous  cell,  and  this  is  introduced  into  a 
beaker  which  serves  as  the  anode  compartment;  or  (b)  two 
glazed  pots  with  small  perforations  are  used,  and  the  small  an- 
nular space  between  these  is  packed  with  asbestos  paper.  If 
necessary  the  liquid  can  be  agitated  by  using  a  rotating  cathode. 

The  reduction  of  nitro-benzene  may  be  cited  as  one  of  the 
best  examples  which  show  the  effect  of  conditions  on  the 
nature  of  the  product: 


4LECTROLYTIO  REDUCTION 


615 


.^- 


3 


Current 
ensity  in 
imperes. 


2 


2 


•II 
•§.« 

•I! 


s 

0    0 


P    O 
03    p, 

S.s 

S  o^ 

i|i 

p  fto 


Cold  satu 
sodic  ca 
ate  soluti 
porous  ce 


8.2 


Jfi 

40  "73 


ncentrated  hy 
drochloric  acid 


616  XLV.   OXIDATION 

In  the  reduction  of  ketonic  compounds,  Tafel  (B.  1900,  33, 
2209)  has  shown  that  the  best  effects  are  obtained  by  using 
pure  lead  electrodes,  as  the  hydrogen  ions  are  thus  discharged 
at  a  higher  potential  than  when  other  metals  are  employed, 
and  by  employing  in  the  cathode  compartment  30-60  per 
cent  sulphuric  acid;  with  stronger  acid,  reduction  of  the  acid 
occurs  and  sulphur  is  deposited.  It  is  also  essential  that  the 
current  density  shall  be  as  low  as  possible.  (For  preparation 
of  cells,  see  Tafel.)  Acetone  when  reduced  under  such  con- 
ditions, using  mercury  as  cathode,  yields  isopropyl  alcohol; 
but  under  similar  conditions  with  a  lead  cathode  it  yields  a 
mixture  of  isopropyl  alcohol  and  pinacone.  Camphor  may  be 
reduced  to  borneol  (p.  568),  and  caffeine  to  deoxy-caffeine  : 

NMe.CO  NMe.CH2 

CO      C-NMe\  —     CO      C-NMex 

.C-N=/  &Me-C.N=/ 


Similarly  uric  acid  may  be  reduced  to  purone  : 
NH-CO  NH-CH2 

CO    C-NHv  —     CO    CH.NH 

NH 


C-NHv  —     CO    CH.NHx 

.C-NH/'  NH.CH-NH/ 


Further,  acetanilide,  CgH5  •  NH  •  CO  •  CH8,  may  be  reduced 
to  ethyl-aniline,  C6H5«NH'CH2«CH3;  pyridine  to  piperidine, 
using  lead  cathodes;  aconitic  acid  to  tricarballylic  acid  and 
cinnamic  to  hydrocinnamic  acid,  by  using  mercury  cathodes. 

The  esters  of  oxalic,  malonic,  acetoacetic,  benzoic,  and 
phthalic  acids,  when  reduced  electrolytically,  yield  ethers,  e.g.: 

Ethyl  benzoate   —  *-  benzyl-ethyl  ether. 


XLV.   OXIDATION 


Oxidation  includes  not  only  those  processes  in  which  oxygen 
is  added  to  a  compound,  e.g.  conversion  of  an  aldehyde,  K  •  CH :  0, 
into  an  acid,  R  •  CO  •  OH,  but  also  processes  in  which  hydrogen 
is  withdrawn  from  a  compound,  e.g.  transformation  of  a  primary 
alcohol,  R.CH2-OH,  into  an  aldehyde,  K-CH:0.  In  certain 
cases  both  processes  can  occur,  e.g.  oxidation  of  aniline, 
CeH6NH2,  to  nitroso-benzene,  C6H6»NO. 


OXIDATION  617 

Moat  of  the  oxidizing  agents  employed  are  substances  rich 
in  oxygen,  e.g.  potassic  dichromate  or  permanganate,  nitric 
acid,  chromic  anhydride,  peroxides,  &c.  During  the  oxi- 
dation, although  the  organic  compound  is  oxidized,  the  Oxi- 
dizing substance  is  reduced,  e.g.  nitric  acid  gives  up  part  of 
its  oxygen  to  the  substance  to  be  oxidized,  and  itself  becomes 
reduced  to  nitrous  acid  or  to  various  oxides  of  nitrogen. 

Oxygen  itself  is  sometimes  made  use  of  as  an  oxidizing 
agent,  but  usually  in  the  presence  of  a  catalyser,  e.g.  finely- 
divided  metals  such  as  platinum  black  or  one  of  the  enzymes 
known  as  oxydases.  Processes  of  oxidation,  like  those  of 
reduction,  depend  not  merely  upon  the  substances  to  be 
oxidized,  but  also  on  the  oxidizing  agent  selected,  and  on 
such  conditions  as  the  acid,  alkaline,  or  neutral  nature  of  the 
solvent,  temperature,  and  concentration.  Examples  of  this 
have  previously  been  cited  among  the  aromatic  hydrocarbons. 
Thus  w-xylene  is  not  acted  upon  by  dilute  nitric  acid,  but 
with  chromic  anhydride  yields  isophthalic  acid.  A  very  good 
example  is  aniline: 

'Manganese  dioxide  and)  .         -,  -,.,.•, 

sulphuric  acid  )   **•  ammonia  and  little  qumone ; 

Dichromate  mixture  — »•  qumone: 

Alkaline  permanganate      — *•  azo-benzene  and  ammonia; 


Acidified  permanganate  — *  aniline  black; 

Neutral  permanganate  — *•  nitro-benzene  and  azo-benzene, 

Bleaching-powder  — »  nitro-benzene; 

.Hypochlorous  acid  — *•  £>-amino-phenol. 

Compounds  of  similar  constitution  are  not  always  oxidized 
in  the  same  manner;  thus,  to  oxidize  j9-nitro-toluene  or  p-nitTO- 
cinnamic  acid  the  best  reagent  is  dichromate  mixture,  but  for 
the  isomeric  0-compounds,  dilute  nitric  acid  or  permanganate 
are  recommended.  The  inhibiting  influence  of  halogen  and 
other  negative  radicals  in  the  o-position  with  regard  to  the 
alkyl  group,  on  the  oxidation  of  such  hydrocarbons  by  means 
of  acid  oxidizing  agents,  has  already  been  referred  to  (p.  436), 
and  also  the  fact  that  the  final  product  of  oxidation  of  a 
benzene  homologue  depends  on  the  number  and  positions  of 
the  side  chains,  and  not  on  their  length,  each  yielding  ulti- 
mately a  C02H  group. 

When  a  compound  like  cymene,  CH3  •  C6H4  •  C3H7,  is  selec 
tively  oxidized,  it  is  usually  the  longer  side  chain  which  is 
first  affected;  and  it  has  been  found  possible,  in  a  few  cases, 
to  carry  the  oxidation  to  a  stage  where  a  long  side  chain  has 


618  XLV.   OXIDATION 

become  only  partially  oxidized,  e.g.  aceto-mesitylene,  CLH2Me3  • 
CO'CHg,  to  mesityl-glyoxylic  acid,  C6H2Me3-CO.C02H;  m- 
butyl  toluene,  CH3'C6H4.C4H9,  by  nitric  acid  at  180°,  to  m- 
mejthyl-phenyl-propionic  acid,  CH3  •  C6H4  •  CH2  •  CH2 .  C02EL 

Cohen  and  Miller  (J.  C.  S.  1904,  174,  1622)  find  that  com- 
pounds containing  chlorine  or  bromine  in  the  meta-position 
with  regard  to  a  methyl  group  are  least  readily  oxidized  by 
nitric  acid,  those  with  similar  substituents  in  the  para-position 
most  readily,  and  those  with  0-chloro-  and  bromo-substituents 
are  intermediate. 

In  certain  cases  of  oxidation,  labile  groups  are  present 
which  have  to  be  protected  from  the  oxidizing  agent;  two 
such  groups  are  the  amino-  and  aid ehydo  -  groups.  An 
amino-  or  imino-group  can  often  be  protected  from  under- 
going oxidation  by  transformation  into  the  acetylated  group 
•  NHAc  or  :NAc,  or  even  better,  into  a  nitroso-derivative, 
:N*NO.  The  further  oxidation  of  an  aldehydo-  to  a  car- 
boxylic  group  can  often  be  prevented  by  the  addition  of  some 
substance  to  the  oxidizing  mixture  which  will  yield  a  spar- 
ingly soluble  compound  with  the  aldehyde;  such  compounds 
are  a  primary  aryl-amine,  which  forms  a  compound  of  the 
type  of  benzylidene-aniline,  C6H6  •  CH :  NC6H5,  sodic  hydric 
sulphite,  or  calcium  naphthionate,  the  calcium  salt  of  1-amino- 
naphthalene-4-sulphonic  acid.  From  the  additive  compound 
to  which  the  last  salt  gives  rise,  the  aldehyde  may  be  ob- 
tained by  distillation  in  steam. 

A.  Potassium  Permanganate, — This  is  the  commonest  and 
one  of  the  most  useful  oxidizing  agents,  as  it  may  be  used 
in 'neutral,  alkaline,  or  acid  solution.  Other  permanganates 
are  also  employed,  e.g.  the  calcium  and  barium  salts,  especially 
for  the  oxidation  of  complex  proteins. 

(a)  Alkaline  Solution. — Even  when  no  alkali  is  added  at  the 
beginning,  the  solution  becomes  alkaline  during  the  reaction. 
The  permanganate,  a  derivative  of  Mn20r,  becomes  reduced 
to  hydrated  Mn02,  and  thus  each  molecule  of  permanganate, 
K2Mn208,  can  yield  three  atoms  of  nascent  oxygen: 

K2Mn2O84-H2O  =  2MnO2-f  2KOH  +  3O. 

When  the  product  formed  is  an  acid,  this  remains  dissolved 
in  the  alkaline  liquid,  and  may  often  be  obtained  by  the 
addition  of  mineral  acid  after  the  manganese  dioxide  has 
been  removed  by  filtration.  In  this  manner,  numerous  ben 
zene  hydrocarbons  and  their  derivatives  can  be  oxidized  to 


OXIDATION  WITH  PERMANGANATE  619 

the  corresponding  acids,  e.g.  ^3-chloro- toluene  to  j9-chloro- 
benzoic  acid,  naphthalene  to  phthalonic  acid,  0-C02H«C6H4» 
CO«C02H.  Other  examples  are  the  conversion  of  o-nitro- 

Slienol  into  dinitro  -  dihydroxy  -  diphenyl,  N02  •  (OH)C6H3  • 
6H3(OH).N02,  and  of  uric  acid  into  allantoin  (p.  294). 

The  oxidation  of  olefine  derivatives  by  two  per  cent  perman- 
ganate (Fittig)  is  of  extreme  interest.  Two  hydroxyl  groups 
are  invariably  added,  and  a  glycol  derivative  formed;  thus 
cinnamic  acid,  C6H,  •  CH :  CH  •  C02H,  yields  phenyl-gly  eerie 
acid,  C6H5.CH(OH).CH(OH).C02H.  When  a  stronger  per- 
manganate solution  or  a  more  powerful  oxidizing  agent  is 
used,  the  unsaturated  compound  is  ruptured  at  the  point  of 
the  double  bond,  and  a  mixture  of  less  complex  acids  or 
ketones  formed. 

An  excess  of  alkali  is  often  added  to  the  permanganate  before 
use.  Under  these  conditions  0-toluic  acid  yields  phthalic  acid, 
and  the  method  is  largely  made  use  of  for  oxidizing  0-sub- 
stituted  derivatives  of  toluene,  &c.  When  the  solution  is  dilute 
and  the  temperature  is  kept  at  0°,  the  oxidation  is  mild,  and 
can  stop  at  the  formation  of  a  glyoxylic  acid,  e.g. : 

C6H2Me3.(X).CH3  —  C6H2Me3.CO.CO2H; 

otherwise  a  substituted  benzoic  acid — in  this  case  C6H2Me3« 
C02H — is  always  formed.  Substituted  cinnamic  acids,  by 
this  method,  can  be  converted  into  corresponding  benzoic 
acids,  e.g. : 

N02(OH)C6H3.CH:CH.C02H    to    N02(OH)C6H3.CO2H. 

Similarly,  hydrocarbons  of  the  type  of  triphenyl-methane, 
CHPhg,  can  be  oxidized  to  carbinols,  e.g.  CPh3-OH,  and 
compounds  of  the  type  of  diphenyl-methane,  CH2Ph2,  to 
ketones,  CPh2-CO. 

(b)  Neutral  Solution, — In  a  few  cases  it  is  necessary  tc 
keep  the  solution  neutral  from  beginning  to  end,  and  this  is 
accomplished  by  the  addition  of  an  excess  of  magnesic  sul- 
phate, which  yields  insoluble  magnesic  hydroxide  with  the 
caustic  potash  produced  during  the  oxidation.     When  acet-o- 
toluidide,   CH3  •  C6H4  •  NH  •  CO  -  CH3,  is  thus  oxidized,  an 
80-per-cent  yield  of  acetanthranilic  acid,  C02H  •  C6H4  •  NH  • 
CO'CH3,  is  formed,  whereas  in  the   presence  of  alkali  the 
yield  is  only  some  30  per  cent. 

(c)  Acid  Solution. — Acetic  or  sulphuric  acid  is  used,  and 
the   acid  is   added  gradually  with  the  permanganate.     The 


620  XLV.  OXIDATION 

method  is  of  use  for  the  preparation  of  very  stable  compounds 
only,  as  the  majority  are  completely  decomposed  by  these 
reagents.  The  reaction  is  quite  different  from  that  in  alka- 
line solution,  the  permanganate  (a  derivative  of  Mn20r)  is 
reduced  to  a  manganous  salt  (derived  from  MnO),  and  thus 
each  molecule  of  permanganate  gives  rise  to  five  atoms  of 
available  oxygen: 

K2Mn2O8  +  3H2S04  =  2MnS04  +  K2SO4  +  3H2O  -f  5O. 

Sulphides  or  hydrosulphides  in  both  the  aliphatic  and  aro- 
matic series  may  be  oxidized  to  sulphonic  acids,  a  reaction 
which  is  useful  for  the  preparation  of  certain  naphthalene- 
sulphonic  acids  which  cannot  be  obtained  by  direct  sulphona- 
tion.  o-Iodo-benzoic  acid  may  be  oxidized  to  o-iodoso-benzoic 
acid,  tetrabromo-p-xylene  to  tetrabromo-terephthalic  acid,  and 
primary  alcohols  to  aldehydes. 

B.  Chromic  Acid  Derivatives,— Chromic  anhydride,  Cr03, 
is  often  used  as  an  oxidizing  agent  when  dissolved  in  glacial 
acetic  acid,  two  molecules  of  the  anhydride  yielding  three  atoms 
of  oxygen,  2  Cr03  =  Cr203  +  30.  Usually  only  the  theoretical 
amount  required  for  the  oxidation  is  used,  and  this  is  gradually 
run  in  from  a  dropping  funnel.  Quinoline  homologues  are 
oxidized  to  quinoline  carboxylic  acids,  and  aromatic  alcohols 
to  aldehydes,  if  a  primary  amine  is  present  to  form  a  Scki/'s 
base  (p.  425).  Even  benzene  homologues  may  be  oxidized  to 
aldehydes  in  the  presence  of  acetic  anhydride,  as  the  acetyl 
derivatives  thus  formed  are  stable. 

Chromyl  chloride,  Cr02Cl2,  the  chloride  of  chromic  acid,  is 
used  for  oxidizing  benzene  hydrocarbons  to  aldehydes  (Etard's 
reaction,  p.  424).  The  usual  method  is  to  dissolve  the  hydro- 
carbon and  chromyl  chloride  separately  in  carbon  disulphide, 
and  to  run  in  the  chloride  solution  until  the  red  colour  per- 
sists, and  then  to  decompose  with  water.  A  precipitate  of  a 
double  compound,  e.g.  C6H5«CH3,  2Cr02Cl9,  is  first  produced, 
and  this  is  decomposed  by  water  according  to  the  equation : 

3[C6H6CH3,2Cr02Cl2]  =  3CCH6CHO  -f  4OCl3-f  2H2CrO4  +  H2O. 

The  usual  method  of  using  chromic  acid  is  in  the  form  of 
a  mixture  of  a  dichroinate  and  sulphuric  acid,  which  react 
according  to  the  equation: 

K20207  +  4H2S04  =  K2S04  -f  Cr2(SO4)3  -f  4H2O  +  3O, 

each  molecule  of  dichromate  yielding  three  atoms  of  available 


OXIDATION   WITH   NITRIC  ACID  621 

oxygen.  Sometimes  potassic  dichromate  is  used,  but  more 
frequently  the  sodic  salt,  as  it  is  cheaper  and  more  readily 
soluble  in  water.  As  a  rule,  the  dichromate  mixture  is  added 
gradually  to  the  oxidizable  substance.  It  is  the  common 
method  of  preparing  aldehydes  from  alcohols  (see  Acetalde- 
hyde,  p.  128),  and  also  from  aromatic  hydrocarbons,  as  there 
is  not  the  same  tendency  for  the  -CHO  group  to  be  further 
oxidized  as  when  permanganate  is  employed.  Complex  alco- 
hols may  also  be  oxidized  to  ketones  or  aldehydes,  e.g.  menthol 
to  menthone  (p.  578).  Many  compounds,  such  as  hydroxy- 
acids,  ketones,  ketonic  acids,  &c.,  are  ruptured  by  chromic  acid 
mixture,  and  acids  or  ketones  containing  a  smaller  number  of 
carbon  atoms  are  formed. 

This  is  the  oxidizing  agent  usually  employed  for  the  pre- 
paration of  quinones,  e.g.  from  aniline,  and  as  a  rule  the  tem- 
perature should  be  kept  at  about  0°.  According  to  Bamberger, 
the  following  series  of  reactions  occur: 

06H6.NH2  -*  C6H6.NH.OH  ->  p-OH.CcH4.NH2  —  O:C6H4:O. 


C.  Nitric  Acid.  —  Examples  of  the  complete  oxidizing  action 
of  fuming  nitric  acid  are  met  with  in  the  ordinary  Carius 
method  for  estimating  halogens  or  sulphur.  One  of  the  chief 
drawbacks  of  nitric  acid  is,  that  in  addition  to  being  an  oxi- 
dizing agent,  it  is  also  a  nitrating  agent,  and  the  products  of 
oxidation,  even  when  dilute  acid  is  used,  contain  smaller  or 
larger  amounts  of  nitro-  derivatives.  By  means  of  dilute 
nitric  acid  many  benzene  homologues  are  oxidized  to  car- 
boxy  lie  acids,  but  the  process  is  slow;  thus  pentamethyl 
benzene  dissolved  in  benzene  requires  sixty  hours'  boiling  to 
oxidize  it  to  tetramethyl-benzoic  acid,  and  slightly  longer 
time  is  required  to  oxidize  2  :  6-chloro-nitro-toluene  to  the 
corresponding  acid.  An  interesting  oxidation  is  that  of 
m-butyl-toluene  to  w-methyl-phenyl-propionic  acid,  and  a 
somewhat  complex  oxidation  is  that  of  camphor  to  cam- 
phoronic  acid  (p.  586).  Kmffl  (R  1889,  21,  2735)  introduced 
the  use  of  concentrated  nitric  acid  (sp.  gr.  1-5)  for  oxidizing 
purposes.  The  admixture  was  effected  at  0°-10°,  the  tem- 
perature gradually  raised  to  50°,  and  the  product  poured  into 
water.  This  is  a  very  good  method  for  oxidizing  compounds 
which  are  already  nitrated,  as  in  other  cases  nitro-derivatives 
are  very  liable  to  be  formed.  Dinitroxylene  is  oxidized  in 
this  way  to  dinitrophthalic  acid.  Sulphoxides,  e.g.  Et2SO, 
may  be  oxidized  to  sulphones,  EtgSO^  iodo-benzoic  acid  to 


622  XLV.   OXIDATION 

iodoso-benzoic  acid,  cane-sugar  to  oxalic  acid,  &c.  The 
method  adopted  in  oxidizing  glycerol  to  glyceric  acid  is  to 
allow  the  aqueous  solution  of  the  glycerol  to  float  on  concen- 
trated nitric  acid. 

A  mixture  of  concentrated  nitric  and  sulphuric  acids,  which 
is  an  extremely  good  nitrating  agent,  may  be  used  for  oxidiz- 
ing purposes,  e.g.  0-nitro-benzyl  alcohol  to  the  corresponding 
aldehyde,  of  ^-nitro-cinnamic  acid  to  ^-nitro-benzaldehyde,  and 
of  5-trinitro-toluene  to  s-trinitro-benzoic  acid. 

D.  Sulphuric  Acid. — One  of  the   oldest  examples  of  the 
oxidizing  action  of   concentrated  sulphuric  acid  is  the  con- 
version  of   ethyl  mercaptan,    C2H6SH,  to   ethyl   disulphide, 
(C2H5)2S2,  and  another  that  of  piperidine  to  pyridine.    Schmidt 
introduced  the  use  of  fuming  sulphuric  acid  (60  or  70  per  cent 
S03)  at  low  temperatures  for  converting  alizarin  and  other 
hydroxy- derivatives   of  anthraquinone  into  tri-  to   hexahy- 
droxy-derivatives,  many  of  which  are  important  dyes.     The 
hydroxy-groups  form  an  ester  with  the  sulphuric  acid,  but  this 
is  readily  hydrolysed  when  boiled  with  dilute  acid.     Concen- 
trated sulphuric  acid  may  also  be  used  for  the  preparation  of 
the  same  compounds,  and  the  yields  are  largely  increased  by 
the  addition  of  boric  acid,  this  being  probably  due  to  the  fact 
that  boric  esters  are  formed,  which  prevent  the  removal  of  the 
hydroxy-groups  when  once  introduced. 

An  oxidizing  action  of  commercial  importance  is  the  con- 
version of  naphthalene  into  phthalic  acid  by  means  of  con- 
centrated sulphuric  acid  and  a  small  amount  of  mercuric 
sulphate  at  a  temperature  above  300°. 

E.  Peroxides. — The  peroxides  mainly  employed  are  Mri02, 
Pb02,  and  occasionally  H20?.     Lead  peroxide  is  frequently 
used  in  the  form  of  a  paste  with  acetic  acid,  one  of  the  earliest 
oxidations  with  this  reagent  being  that  of  uric  acid  to  allan- 
toin  (p.  294).      Characteristic  oxidations  are  (i)  that  of  a- 
hydroxy-acids  to  aldehydo-acids,  with  one  less  carbon  atom 
(p.  305),  e.g.: 

C02H.CH(OH).CH2.CO2H  -*  CO2  +  0:CH.CH2.CO2H; 

(ii)  of  alkyl  acetates  to  aldehydes,  e.g. : 

o-N02.C6H4.CH2.O.CO.CH3    to    o-N02.C6H4.CH:O; 

(iii)  of  triphenyl-methane-derivatives  to  the  corresponding 
carbinols,  the  salts  of  which  are  dyes,  e.g.: 


OXIDATION   WITH  PEROXIDES  623 

and  (iv)  of  amino-hydroxy-derivatives  of  anthraquinone  to  the 
corresponding  polyhydroxy-derivatives,  the  NH2  being  replaced 
by  OH,  a  reaction  which  does  not  occur  when  the  amino-group 
is  acetylated.  Manganese  dioxide  alone,  or  in  the  presence 
of  sulphuric  acid,  may  be  used  for  converting  CH3  groups  in 
benzene  homologues  into  aldehydo-groups.  The  mixture  is 
kept  stirred,  and  an  excess  of  hydrocarbon  is  always  present. 
Benzaldehyde,  o-chloro-benzaldehyde,  j?-nitro-benzaldehyde, 
terephthalic  aldehyde,  &c.,  have  been  prepared  by  this  method. 
A  remarkable  oxidation  is  that  of  benzene  to  benzoic  acid  by 
means  of  the  peroxide  and  sulphuric  acid.  Hydroxy-acids 
are  often  ruptured  by  these  reagents,  e.g.  lactic  acid,  CH3- 
CH(OH)-C02H,  yields  aldehyde  and  carbonic  acid.  This  is 
the  basis  of  a  method  for  estimating  the  strength  of  solutions 
of  lactic  acid  by  determining  the  amount  of  aldehyde  formed. 
The  same  reagents  are  also  used  for  the  oxidation  of  alkaloids, 
and  for  the  conversion  of  the  leuco-bases  of  triphenyl-methane 
dyes  into  the  dye  salts,  e.g.  jp-leucaniline  into  ^-rosaniline. 
Hydrogen  peroxide  is  often  used  in  the  presence  of  potassium 
hydroxide  for  the  preparation  of  organic  peroxides,  e.g.  diethyl- 
peroxide,  Et202,  benzoyl-peroxide,  (C6H5CO)202.  Piperidine, 
when  oxidized  with  three  per  cent  peroxide  solution,  yields 
glutaric  acid  owing  to  the  rupture  of  the  ring.  Benzene,  with 
the  peroxide,  yields  a  certain  amount  of  phenol.  Azo-com- 
pounds  are  converted  into  corresponding  azoxy-derivatives, 
and  phenols  into  dihydric  phenols  or  quinones.  Fatty  acids 
are  converted  into  ketones,  E-CHg-CO-OH  —  K«CH2.  CO- 
CKLE, (DaMn,  Am.  C.  J.  1910,  44,  41). 

Fenton  and  others  (J.  C.  S.  1894,  899;  1895,  48,  774;  1899, 
1)  have  made  use  of  hydrogen  peroxide  in  the  presence  of 
small  amounts  of  ferrous  salts;  by  this  method  the  following 
reactions  have  been  effected: 

Glycollic  acid,  OH-CH2.COSH,  —>  glyoxylic  acid,  CHO-C02H; 

Lactic  acid,  CH3.CH(OH).C02H,  •—  pyruvic  acid,  CH8.CO-C02H; 

Tartronic  acid,  OH  •  CH(C02H)2,  -*  mesoxalic  acid,  CO(C02H)2; 

Gly eerie  acid,  \  fhydroxy-ruvic  acid 

H        OH.CH2.CH(OH).C02H,j  '    '  \ 

Tartario  acid,                _^ 1  ,  /dUiydroxy^maleic :  acid, 


COaH.CH(OH).CH(OH).C02H,/  '    *  I  COaH.C(OH):C(OH).C02H; 
Polyhydric  alcohols,  — *•  aldoses. 

F.  Oxygen  itself  can  often  be  used  for  oxidation,  generally 
in  the  presence  of  platinum  black  or  platinized  asbestos.  Denn- 
stedt's  method  for  estimating  carbon  and  hydrogen  in  organic 


624  XLV.    OXIDATION 

compounds  is  based  on  this.  Many  aldehydes,  when  exposed 
to  moist  air,  are  transformed  into  acids;  thus  specimens  of 
benzaldehyde  which  have  been  kept  for  some  time  contain 
appreciable  amounts  of  benzoic  acid.  Cinnamic  alcohol  may 
be  oxidized  to  cirmam  aldehyde,  glycerol  to  glyceraldehyde, 
and  methyl  alcohol  to  formaldehyde  in  presence  of  slightly 
oxidized  copper.  Alkaline  solutions  of  polyhydroxylic  phenols 
are  readily  oxidized  (see  Pyrogallol),  and  a  similar  solution  of 
gallic  acid  yields  the  yellow  dye  galloflavin.  Glock  has  shown 
that  methane  and  air,  when  repeatedly  passed  over  heated 
metallic  copper  at  600°,  yield  methyl  alcohol  and  formalde- 
hyde, and  that  ethane  and  air  yield  ethyl  alcohol,  acetalde- 
hyde,  and  acetic  acid.  [Compare  also  Bone's  experiments  (pp. 
36  and  37).]  Ozone  may  also  be  used  as  an  oxidizing  agent; 
it  is  employed  commercially  for  refining  oils,  &c.  (cf.  J.  Ind. 
1898,  1101).  G.  Harries  (A.  1905,  343,  311;  1910,  374,  288) 
has  examined  the  action  of  ozone  on  various  types  of  carbon 
compounds,  mainly  in  glacial  acetic  acid  solution.  Methane, 
ethyl  alcohol,  &c.,  are  oxidized  to  aldehydes  and  acids,  hydro- 
gen peroxide  also  being  formed.  Saturated  aldehydes  and, 
to  a  certain  extent,  ketones  yield  labile  peroxides  of  the  type, 
R  •  CH :  0  :  0.  Most  unsaturated  hydrocarbons  and  alcohols 
combine  with  ozone,  yielding  ozonides,  e.g.  C2H4-J-03,  ethylene 
ozonide.  The  structure  of  such  compounds  is  usually  repre- 
sented as  follows,  e.g.: 

•CH2 


and  for  each  ethylene  linking  one  molecule  of  ozone  is  added. 
Many  compounds  combine  with  more  than  this  amount  of 
ozone,  yielding  oxozonides,  e.g.  propylene  yields  a  product, 
C3H6-}-04,  which  are  not  readily  transformed  into  normal 
ozonides.  They  are  regarded  as  derived  from  the  hypothetical 
04.  Unsaturated  carbonyl  derivatives,  e.g.  acids,  aldehydes, 
and  ketones,  also  combine  with  ozone,  yielding  ozonides;  they 
can,  however,  combine  with  a  fourth  atom  of  oxygen,  yielding 
perozonides,  which  are  decomposed  by  water,  yielding  the 
ozonide  and  hydrogen  peroxide.  The  three  atoms  of  the 
ozonide  are  regarded  as  attached  to  the  two  carbon  atoms 
of  the  ethylene  linking,  whilst  the  fourth  atom  is  attached 
to  the  carbonyl  group.  Oleic  acid  perozonide  is  represented 
Mi 


OXIDATION  WITH  OZONE  625 


CH3.[CH2]r.CH  .  C 

O-O-O  OH 

The  ozonides  are  decomposed  when  gently  heated,  or  when 
the  solutions  in  glacial  acetic  acid  are  warmed.  Oleic  acid 
ozonide  decomposes  into  the  four  products: 


CH3.[CH2]7.CH:0  + 

I.  Nonaldehyde.          QS  IL 


and    C 

III.  Nonaldehyde     NU      IV.  Azelaic  acid  semi- 
peroxide.  aldehyde. 

Some  of  these  products  are  readily  oxidized,  e.g.  nonalde- 
hyde yields  the  corresponding  acid,  and  the  semialdehyde 
yields  azelaic.  At  the  same  time  the  aldehyde  peroxides  are 
transformed  into  the  isomeric  carboxylic  acids,  so  that  appreci- 
able amounts  of  nonylic  and  azelaic  acids  are  always  found  in 
the  final  decomposition  products.  The  nonaldehyde  peroxide 
formed  in  this  way  is  isomeric,  and  not  identical  with  the  per- 
oxide obtained  by  the  direct  action  of  ozone  on  the  aldehyde. 
It  is  more  stable,  has  m.-pt.  73°,  and  is  represented  by  for- 
mula III. 

Such  decompositions  of  ozonides  can  be  used  for  determin- 
ing  the  position  of  the  ethylene  linking  in  the  molecule  of  the 
original  compound,  and  also  for  the  preparation  of  certain 
aldehydes,  aldehydic  acids,  and  dialdehydes. 

Benzene  yields  a  highly  explosive  triozonide,  (LHgOg. 

G.  Other  Oxidizing  Agents.  —  Chlorine  and  bromine  are 
generally  used  in  alkaline  solution,  i.e.  in  the  form  of  hypo- 
chlorite  or  hypobromite.  As  examples,  we  have  the  well- 
known  Hofmann  reaction,  the  conversion  of  amides,  and  imides 
such  as  succimmide  and  phthalimide,  into  amines  or  nitriles 
(pp.  183  and  184);  also  the  oxidation  of  reduced  benzene 
derivatives  back  to  the  original  benzene  compound.  An  in- 
teresting oxidation  is  that  of  benzylidene-acetone  to  cinnamic 
acid  with  four  per  cent  sodium  hypobromite  : 

C6H6  .  CH  :  CH  -  CO  •  CH3  -f  3  NaBrO 


and  of  potassium  cyanide  to  cyanate  by  hypochlorite.   Bromine 
water  itself  is  frequently  used  for  the  oxidation  of  sugars,  e.g. 

(8480)  8& 


626  XLV.    OXIDATION 

of  an  aldose  to  the  corresponding  monobasic  acid;   thus  gly- 
cerose  to  gly  eerie  acid,  glucose  to  gluconic  acid. 

Less  common  oxidizing  agents  are  potassic  ferricyanide, 
which  is  reduced  to  the  f  errocyanide  : 

2K3FeC6N6  +  2KOH  =  2K4FeC6N6  +  H2O  +  0. 


s-Trinitro-benzene  may  be  oxidized  by  this  reagent  to  picric 
acid,  phenyl-acetylene  to  diphenyl-diacetylene,  CPh:C«C:CPh, 
nitroso-  to  nitro-  derivatives,  quinone-dioxime  to  dinitroso- 
benzene,  benzene-diazo-oxides  to  salts  of  benzene-diazoic  acid, 
C6H5  •  N  :  NO  •  OH,  and  nitro-toluenes  to  nitro-benzoic  acids. 
Ferric  chloride: 

2FeCl3  +  H20  =  2FeCl2  +  2HCl  +  0, 

may  be  used  for  oxidizing  hydroxylamine  derivatives  to 
nitroso-compounds,  e.g.  : 

C6H4Br.NH.OH  -»•  C6H4Br.NO; 

quinols  to  quinones,  and  naphthols  to  dinaphthols: 
OH.C10H6.C10H6.OH. 

Silver  oxide  oxidizes  glycerol  to  glycollic  acid,  and  gener- 
ally aldehydes  to  acids,  and  0-dihydroxy-benzene  to  0-benzo- 
quinone.  Mercuric  oxide,  usually  with  alkali,  e.g.  barium 
hydroxide,  is  used  for  oxidizing  fructose  to  trihydroxy-butyric 
acid  and  glycollic  acid,  and  glucose  to  gluconic  acid.  It  also 
oxidizes  unsym.  diethyl  -  hydrazine  to  tetraethyl  -  tetrazone, 
NEt2  •  N  :  N  •  NEt2,  and  sym.  diethyl  -hydrazine  to  mercury- 
diethyl,  nitrogen,  and  water.  Nitre-benzene  is  used  as  an 
oxidizing  agent  in  the  manufacture  of  magenta  (p.  487),  and 
also  in  the  Skraup  synthesis  of  quinoline  (p.  542).  Potassium 
persulphate,  mixed  with  concentrated  sulphuric  acid,  is  known 
as  Caro's  reagent  or  sulphomono-per-acid,  and  can  oxidize  sali- 
cylic acid  to  2:5-dihydroxy-benzoic  acid.  It  is  also  used  for 
oxidizing  various  terpene  derivatives,  and  readily  oxidizes  aro- 
matic primary  amines  to  nitroso-derivatives,  e.g.  : 

CflH5NH2  —  C6H6NO. 

H.  Electrolytic  Oxidation.  —  Organic  compounds  may  be 
oxidized  by  means  of  the  oxygen  formed  at  the  anode  of  an 
electrolytic  cell.  The  method  is  not  so  general  in  application 
as  electrolytic  reduction,  as  it  is  extremely  difficult  to  stop 
the  reaction  at  the  right  point.  Even  when  the  theoretical 


ELECTROLYTIC  OXIDATION  627 

amount  of  oxygen  has  been  formed,  it  is  often  found  that 
part  of  the  compound  is  unacted  on,  and  part  has  been  com- 
pletely oxidized.  The  following  are  fairly  typical  examples : — 

Purpuro-gallin  is  formed  by  the  electrolysis  of  a  solution 
of  pyrogallol  in  sodium  sulphate  solution,  using  a  rotating 
platinum  anode  of  2  sq.  dm.  The  reaction  is  complete  after 
6-8  hours  with  a  C.D.  of  1-5-2  amperes  and  an  E.M.F.  of 
4-3-4-5  volts. 

Anthraquinone  may  be  prepared  by  oxidizing  an  emulsion 
of  anthracene,  water,  and  sulphuric  acid,  using  a  rotating  lead 
cathode,  and  a  leaden  vessel  as  anode.  The  best  yields  are 
obtained  when  an  oxygen  carrier,  e.g.  manganese  sulphate,  is 
employed  with  a  temperature  of  75°-90°,  a  C.D.  of  1-2  am- 
peres, and  an  E.M.F.  of  2'8-3'5  volts. 

Numerous  azo-dyes  have  been  obtained  electrolytically; 
thus,  Orange  II,  or  fi  -  naphthol  -  azo benzene  -  sulphonic  acid, 
OH.S02.e6H4.N:N.C10Hfl.OH  (p.  502),  is  produced  from 
an  aqueous  solution  containing  sodic  sulphanilate,  /3-naphthol, 
and  sodic  nitrite.  The  cathodes  of  nickel  or  platinum  wire 
are  placed  in  two  separate  cathodic  compartments  consisting 
of  small  porous  cells  and  containing  sodic  hydroxide  solution. 
The  rotating  anode  is  of  platinum;  and  a  C.D.  of  8-12  am- 
peres, an  E.M.F.  of  15-18  volts,  and  as  low  a  temperature  as 
possible,  give  the  best  results.  The  homologues  of  benzene, 
when  oxidized  with  platinum  electrodes  in  the  presence  of 
sulphuric  acid  and  acetone,  yield  aldehydes,  e.g.  toluene  — * 
benzaldehyde,  o-xylene  — *  o-toluic  aldehyde,  but  the  yields, 
as  a  rule,  are  not  good.  Ortho-substituents  of  a  negative  char- 
acter tend  to  inhibit  such  oxidations.  Acetic  acid  solutions 
of  p-  and  o-nitro-toluenes  yield  the  corresponding  nitro-benzyl 
alcohols,  whereas  the  m-compound  yields  m-nitro-benzaldehyde. 
Benzyl  sulphide  yiolds  benzylsulphoxide,  benzyldisulphoxide, 
or  tribenzylsulphonium  sulphate  according  to  conditions. 


XLVI.  STEREO-CHEMISTRY  OF  SULPHUR, 
SELENION,   TIN,   AND   NITROGEN   COMPOUNDS 

Attention  has  already  (pp.  154  and  213)  been  drawn  to  the 
fact  that  a  compound  containing  an  asymmetric  carbon  atom, 
Ca,  b,  c,  d,  exists  in  two  optically  active  isomerides  which 
can  unite  to  form  a  racemic  compound.  The  researches  of 
Pope  and  others  within  the  past  few  years  have  proved  that 
compounds  containing  other  quadravalent  atoms,  such  as 


628  XLVI.    STEREO-CHEMISTRY  OF  SULPHUR,   ETC. 

S,  Se,  and  Sn,  attached  to  four  different  univalent  radicals, 
also  exist  in  optically  active  isomeric  forms. 

A.  Sulphur  Compounds  (Pope  and  Peachey,  J.  C.  S.  1900, 
1072).  —  The  sulphur  compounds  selected  were  derivatives 
of  methylethylthetine  bromide: 


a  product  which  can  be  prepared  by  the  addition  of  bromo- 
acetic  acid  to  methylethyl  sulphide.  The  bromide  was  mixed 
with  the  theoretical  amount  of  silver  d-camphor-sulphonate  in 
aqueous  solution,  the  silver  bromide  removed,  the  filtrate  evap- 
orated at  40°,  and  the  solid  residue  crystallized  some  40-50 
times  from  a  mixture  of  absolute  alcohol  and  dry  ether.  The 
sparingly  soluble  ^-methylethylthetine  d-camphor-sulphonate, 
CHCH  •  CO 


melts  at  118°-120°,  and  has  a  molecular  rotation  [M]D*  = 
+  68°.  The  rotation  for  the  camphor  -  sulphonate  ion  is 
4-51-7°,  and  this  gives  a  rotation  of  +16-3°  for  the  thetine 
ion.  A  very  similar  value  has  been  obtained  by  repeatedly 
crystallizing  the  d-  bromo-  camphor  -sulphonate.  The  corre- 
sponding platinichloride,  (SMeEtCl-CH2.C02H)2,  PtCl4,  has 
a  molecular  rotation  +  30'2°. 

Smiles  (J.  C.  S.   1900,  1174)  has  obtained  methylethyl- 
phenacylsulphine  bromide: 


(from  methylethyl  sulphide  and  bromo-acetophenone)  in  opti- 
cally active  modifications  by  a  similar  process. 

B.  Selenion  Compounds  have  been  resolved  by  Pope  and 
Neville  (J.  C.  S.  1902,  1552).  The  compound  used  was 
methylethylselenetine  bromide,  SeMeEtBr  •  CH2  •  C02H,  ob- 
tained from  methylethyl  selenide  and  bromo-acetic  acid;  the 
corresponding  d-  bromo  -camphor-  sulphonate  was  repeatedly 
crystallized  from  alcohol,  and  the  least  soluble  fraction  melted 
at  168°,  and  had  [M]D  =  +330-8,  which  gives  a  rotation  of 
+  60-8  for  the  methylethylselenetine  ion. 

The  corresponding  salt  of  the  /-base  -f  d-acid  was  isolated; 
it  melted  at  151°,  and  had  [M]D  =  +209  '6,  which  gives  a 
value  of  —60  '4  for  the  Z-selenetine  ion.  The  platinichloride 

*  For  meaning  of  this,  see  p.  627. 


OPTICALLY  ACTIVE  TIN   COMPOUNDS  629 

had   a  molecular  rotation   +55°,   but  the  mercuri  -  iodide, 
SeMeEtI.CH2.C02H,  HgI2,  was  optically  inactive. 

C.  Tin  Compounds  (Pope  and  Peachey,  P.  1900,  42,  and 
116).  —  A  compound  containing  an  asymmetric  tin  atom  was 
prepared  by  the  following  series  of  reactions: 


2SnMe3I  +  ZnEt2  =  2SnMe3Et  +  ZnI2; 
SnMegEt  +  12  =  SnMe2EtI  +  Mel; 
2SnMe2EtI  +  ZnPr2  =  2SnMe2EtPr  +  ZnI2; 
SnMe2EtPr  +  I2  =  SnMeEtPrI  +  Mel. 

The  methylethylpropyl-tin  iodide  (a  liquid  boiling  at  270°) 
was  converted  into  the  ^-camphor  -sulphonate  by  means  of 
silver  d-  camphor  -sulphonate,  and  after  the  removal  of  the 
silver  iodide  the  solution  was  evaporated,  when  crystals  of 
d-methylethyl-7i-propyl-tin  ^-camphor-sulphonate,  SnMeEtPr- 
O  •  S02  •  C1?H150,  melting  at  125°-126°,  were  obtained.  In 
aqueous  solution,  [M]D  =  +95°,  which  gives  a  value  for  the 
univalent  ion,  SnMeEtPr,  of  about  -f  45°.  When  the  mother 
liquor  from  the  above-mentioned  crystals  is  evaporated,  a 
further  quantity  of  the  same  compound  is  obtained,  and  the 
operation  can  be  continued  until  all  the  water  has  been 
expelled.  No  trace  of  /-methylethylpropyl-tin  d-camphor- 
sulphonate  can  be  isolated.  Pope  and  Peachey  attribute  this 
to  the  conversion  of  the  /-base  into  the  d-base  by  continued 
racemization  (p.  257),  in  the  following  manner:  —  The  solution 
of  the  racemic  base  with  the  d-acid  deposits  a  portion  of  its 
d-base  as  the  sparingly  soluble  salt  d-base  +  d-acid;  the  excess 
of  I-  over  d-base  remaining  in  the  solution  racemizes  as  eva- 
poration proceeds,  a  further  quantity  of  J-base  separates  as 
salt,  and  racemization  of  the  residue  again  proceeds. 

A  d-methylethyl-w-propyl-tin  iodide  with  [a]D  +  23°  in 
ethereal  solution  has  been  prepared  from  the  camphor- 
sulphonate. 

The  resolution  of  tin  compounds  has  also  been  accomplished 
by  means  of  the  d-bromo-camphor-sulphonate.  If  the  aqueous 
solution  of  rf-methylethyl-n-propyl-tin  d-bromo-camphor-sul- 
phonate  is  heated  at  100°  in  a  sealed  tube  for  two  hours, 
racemization  proceeds,  and  the  rotation  [M]D  -f  272°  is  that 
due  to  bromo-camphor-sulphonate  ion  only. 

D.  Silicon  Compounds.  —  Silicon  is  the  element  most  closely 
allied  to  carbon,  and  hence  numerous  attempts  have  been 
made  to  prepare  optically  active  silicon  compounds  containing 
an  asymmetric  silicon  atom. 


630  XLVI.    STEREO-CHEMISTRY   OF  SULPHUR,    Eta 

It  is  only  recently,  however,  that  these  experiments  have 
met  with  success.  Kipping  (J.  C.  S.  1907,  91,  209)  has  pre- 
pared the  compound 


ethylpropylbenzylphenylsilicane,  by  the  following  series  of  re- 
actions :  — 

SiCl4  +  MgEtBr  =  SiEtCl3  +  MgClBr 

SiEtCL  -f-  MgPhBr  =  SiEtPhCl2  +  MgClBr 

SiEtPhCL  +  MgPrBr  =  SiEtPhPrCl  -f  MgClBr 

SiEtPhPrCl  -f  MgBzCl  =  SiEtPhPrBz  -f  MgCl2. 

This  hydrocarbon  when  sulphonated  gives  rise  to  benzene 
and  a  sulphonic  acid: 

S03H  •  C6H4  •  CH2  •  SiEtPr  •  0  •  SiEtPr  •  CH2  •  C0H4  •  S03H, 

sulphobenzylethylpropylsilicyl  oxide.  As  the  formula  indi- 
cates, this  compound  contains  two  similar  asymmetric  silicon 
atoms,  and  should  presumably  exist  in  the  same  number  of 
isomeric  modifications  as  tartaric  acid  (p.  249).  One  of  the 
acids  isolated  by  Kipping  has  been  shown  to  be  a  ^-/-compound, 
and  its  salt  with  the  active  base,  d-methylhydrindamine  can 
be  resolved  into  its  optically  active  components  when  re- 
peatedly crystallized  from  acetone  or  aqueous  methyl  alcohol. 
The  two  acids  have  extremely  low  rotatory  powers,  e.g.  [a]D 
±  3°  to  4°.  Similar  active  compounds  containing  an  isobutyl 
in  place  of  the  propyl  group  have  been  obtained;  they  have 
[a]D  ±  10'5°.  And  still  more  recently  compounds  containing 
a  single  asymmetric  silicon  atom  have  been  isolated,  e.g. 
ethylpropyldibenzylsilicanemonosulphonic  acid, 

CH2Ph  •  SiEtPr  •  CH2  •  CflH4  •  S03H, 

which  can  be  resolved  into  active  components  by  means  of 
brucine.  Most  of  the  active  silicon  derivatives  are  character- 
ized by  the  close  similarity  between  the  active  and  racemic 
forms  and  by  the  low  rotatory  powers,  so  that  it  is  difficult 
to  say,  in  certain  cases,  whether  resolution  has  been  effected 
or  not. 

Pope  and  PeacJiey  conclude  that  all  the  elements  of  Group  IV 
of  the  Periodic  Classification,  namely  C,  Si,  Ti,  Ge,  Zr,  Sn,  Ce, 
Pb,  Th,  also  probably  O,  S,  Se,  Te,  should  in  a  similar  manner 
give  rise  to  optical  activity  in  their  asymmetric  derivatives. 


OPTICALLY  ACTIVE  NITROGEN   COMPOUNDS  631 

E.  Nitrogen  Compounds  (H.  0.  Jones,  B.  A.  Eep.  1904, 169).— 
(i)  Terwlent  Nitrogen  Compounds. — No  optical  activity  has  been 
met  with  in  compounds  of  the  type  N  a,  b,  c,  and  all  attempts 
to  resolve  such  compounds  have  proved  fruitless.  Jones  and 
Millington  (C.  C.  1904,  2,  952)  have  attempted  to  resolve 
benzyl -phenyl-hydrazine  by  means  of  d- camphor -sulphonic 
acid,  and  to  resolve  methylethylaniline  -  sulphonic  acid  by 
means  of  brucine.  Other  chemists  (Krafft,  Behrend  and  Konig, 
Ladenburg)  have  attempted  to  resolve  benzyl  -  ethyl  -  amine, 
p-tolyl-hydrazine,  /?-benzyl-hydroxylamine,  methyl-aniline,  and 
tetra-hydroquinoline  by  means  of  d-tartaric  acid. 

Kipping  and  Salway  (J.  0.  S.  1904,  438)  have  adopted  the 
method  of  treating  a  secondary  amine  with  a  racemic  acid 
chloride,  namely  2-/-benzylmethylacetyl  chloride,  CHMeB2^ 
COC1,  and  examining  the  substituted  acid  amide  formed. 
With  a  true  d-/-base,  the  following  compounds  should  be 
formed:  dBdA,  IB  I  A,  dElA,  ZBdA,  of  which  1  and  2  form 
an  enantiomorphously  related  pair,  and  3  and  4  a  similar  pair. 
Thus  the  complete  product  would  be  a  mixture  of  two  racemic 
substituted  acid  amides.  Experiments  conducted  with  methyl- 
aniline,  ^?-toluidine,  phenyl-hydrazine,  and  benzyl-aniline  gave 
a  homogeneous  product  in  each  case.  Similarly,  when 
p-toluidine  and  benzyl-aniline  are  condensed  with  d-methyl- 
benzylacetyl  chloride,  no  indication  of  the  formation  of  iso- 
merides  is  met  with. 

A  pair  of  compounds,  C6H3Me2  •  NH .  CHMe  -  CH2  •  CHO, 
containing  tervalent  nitrogen  and  stated  to  be  stereoisomeric, 
have  been  shown  by  Jones  and  White  (J.  C.  S.  1910,  632)  to 
be  structurally  isomeric. 

The  general  conclusion  to  be  drawn  is,  that  the  centres  of 
gravity  ]of  the  three  radicals,  and  also  of  the  nitrogen  atom 
itself,  lie  in  a  single  plane,  and  the  whole  arrangement  is  the 
most  symmetrically  possible  one.  (Cf.  Oximes,  pp.  138,  429.) 

(ii)  Quinquevalent  Nitrogen  Compounds. — (For  formation,  see 
pp.  105,  379.)  The  most  interesting  type  of  compound  is 
that  in  which  all  five  radicals  are  different,  e.g.  N  a,  b,  c,  d,  X. 
These  compounds  are  quaternary  ammonium  salts,  in  which 
four  of  the  radicals  are  alkyl  groups,  and  the  fifth  an  acid 
group.  No  cases  of  inactive  isomerides  have  been  met  with. 
An  example  described  by  JFedekind,  viz.  methylallylphenyl- 
benzylammonium  iodide,  has  recently  been  shown  by  H.  0. 
Jones  (J.  C.  S.  1905,  1721)  to  be  non-existent. 

The   only   known   examples   of   stereoisomerides   are   the 


632  XLVI.    STEREO-CHEMISTRY  01*  SULPHUR,    ETC. 

optically  active  modifications  in  which  compounds  of  the 
type  methylethylpropylisobutylammonium  chloride,  N(CH3) 
(C2H5)(C3H7)(C4H9)C1,  exist.  This  type  of  compound  is 
always  obtained  in  an  inactive  form  when  synthesised  in  the 
laboratory  by  the  addition  of  an  alkyl  haloid  to  a  tertiary 
amine.  In  1891  Le  Bel  claimed  to  have  obtained  a  Icevo-modi- 
fication  by  means  of  penicillium  glaucum  (green  mould),  and  in 
1899  he  confirmed  this  result.  In  the  same  year  Pope  and 
Peachey  (J.  C.  S.  1899,  1127)  obtained  a  resolution  of  Wede- 
Jcind's  benzylphenylallylmethylammonium  iodide  by  the  aid  of 
silver  d-camphor-sulphonate. 

When  the  mixture  of  benzylphenylallylmethylammonium 
d-camphor-sulphonates  is  crystallized  from  acetone,  a  sparingly 
soluble  fraction  is  obtained,  and  this,  when  treated  with 
potassium  iodide,  yields  an  optically  active  iodide,  N(C7H7) 
(C6H5)(C3H5)(CH3)I,  with  [M]D+  192°. 

H.  0.  Jones  (J.  C.  S.  1903,  1418;  1904,  223)  has  resolved 
phenylbenzylmethylethylammonium  iodide  and  phenylmethyl- 
ethylallylammonium  iodide  by  means  of  silver  d-bromo-camphor- 
sulphonate.  Jones  has  observed  that  many  of  these  salts  show 
a  tendency  to  undergo  racemization,  and  during  the  fractional 
crystallization  of  the  salts  it  is  advisable  to  keep  the  tempera- 
ture as  low  as  possible.  Auto-racemization  (p.  257)  occurs 
when  the  cold  chloroform  solutions  are  kept  in  the  dark,  a 
phenomenon  also  observed  by  Pope  and  Harvey  (J.  C.  S.  1901, 
828)  with  other  optically  active  ammonium  salts,  and  probably 
due  to  a  partial  dissociation  of  the  quaternary  ammonium  salt 
into  tertiary  amine  and  alkyl  iodide  and  subsequent  recombina- 
tion. (For  other  optically  active  ammonium  salts,  see  Wedekind, 
B.  1905,  38,  1838;  Thomas  and  Jones,  J.  C.  S.  1906,  280.) 

Quinquevalent  nitrogen  derivatives  of  the  type  Na2bcX, 
e.g.  phenylallyldimethylammonium  iodide,  phenyldipropyl- 
methylammonium  iodide,  &c.,  do  not  exist  in  isomeric  modi- 
fications, and  attempts  to  resolve  such  compounds  into  optically 
active  components  have  given  negative  results  (J.  C.  S.  1897, 
522;  1903,  1141,  1406;  1904,  412).  Aschan  (Zeit.  phys.  1903, 
46,  304)  has  prepared  isomeric  cyclic  nitrogen  compounds 
containing  two  quinquevalent  nitrogen  atoms,  viz.: 


Br  Br 

The  one  compound  is  formed  by  the  union  of  ethylene-di- 


OPTICALLY  ACTIVE  NITROGEN  COMPOUNDS  633 

peridide  with  trimethylene  bromide,  and  the  other  by  the 
combination  of  trimethylene-diperidide  with  ethylene  bromide. 
This  isomerism  can  be  accounted  for  if  the  bromine  atoms  and 
the  central  ring  lie  in  one  plane  and  the  other  rings  in  a  plane 
at  right  angles  to  the  first. 

A  similar  compound  containing  one  nitrogen  atom, 


has  been  shown  by  Scholz  (B.  43,  2121)  to  exist  in  two  opti- 
cally active  forms. 

Methylethylaniline  oxide,  NMeEtO,  has  been  resolved  into 
active  modifications  by  means  of  bromocamphorsulphonic  acid. 
The  base  itself,  probably  NMeE^OH)^  has  [a]D-25°.  The 
compound 

I  •  NMeEtPh  -  CJJ2  •  CH2  •  CH2  .  NMeEtPhI, 

containing  two  similar  asymmetric  nitrogen  atoms,  like  tar- 
taric  acid,  exists  in  two  inactive  forms,  but  so  far  neither  has 
been  resolved  into  active  components.  When  an  asymmetric 
nitrogen  atom  is  introduced  into  a  compound  already  con- 
taining an  asymmetric  carbon  atom,  two  stereoisomerides  are 
formed,  just  as  two  products  are  formed  when  a  new  asym- 
metric carbon  atom  is  introduced  into  an  active  compound. 

One  of  the  simplest  spatial  arrangements  of  the  radicals 
attached  to  a  quinquevalent  nitrogen  atom  is  that  suggested 
by  Bischoff  and  accepted  by  Jones.  The  nitrogen  atom  is 
supposed  to  be  situated  at  the  centre  of  a  pyramid  on  a  rect- 
angular base,  and  the  five  radicals  at  the  five  solid  angles,  the 
four  alkyl  groups  occupying  the  four  angles  of  the  base,  and 
the  acid  radical  occupying  the  angle  at  the  apex.  Since  the 
three  radicals  in  a  tertiary  amine  all  lie  in  one  place,  it  follows 
that  in  the  conversion  of  a  tertiary  amine  into  a  quaternary 
ammonium  salt  a  change  of  "valency  direction"  occurs. 

The  equilibrium  positions  of  the  radicals  in  the  tervalent 
nitrogen  compound  are  disturbed,  and  new  positions  must  be 
found,  which  for  any  four  alkyl  groups  must  be  determined 
jointly  by  the  forces  between  these  radicals  and  the  nitrogen 
atom,  and  the  mutual  forces  exerted  by  the  groups  on  one 
another;  consequently  there  will  be  some  definite  spatial 
arrangement  around  the  nitrogen  atom.  The  fifth  group, 
which  is  always  different  in  character  from  the  other  four, 
will  always  bear  approximately  the  same  relation  to  each  of 


634  XLVI.   STEREO-CHEMISTRY  OF  SULPHUR,   ETC. 

these  four  groups;  in  other  words,  it  occupies  the  apex  of  the 
pyramid,  and  it  is  improbable  that  it  should  ever  take  the  place 
of  an  alkyl  group  at  the  base  of  the  pyramid.  The  relative 
positions  of  the  four  alkyl  radicals  at  the  base  of  the  pyramid 
is  fixed  by  the  forces  exerted  by  these  radicals  on  one  another. 

F.  Phosphorus  Compounds. — Meisenheimer  and  Lichtenstadt 
(B.  1911,  44,  356)  have  obtained  methylethylphenylphosphine 
oxide,  0:PMeEtPh,  in  optically  active  forms.     The  base  was 
prepared   by  combining   methyl   iodide  with   ethyldiphenyl- 
phosphine,  liberating  the  base  with  moist  silver  oxide  and 
then  distilling,  and  was  resolved  by  means  of  d-bromocamphor- 
sulphonic  acid.     The  base  has  [a]D  -f-  33 '8  in  benzene  solution. 
Somewhat  similar  experiments  of  Caven  (J.  C.  S.  1902,  1362) 
and  Ephraim  (B.  1911,  44,  631)  have  given  negative  results. 

G.  Cobalt  Compounds.— Werner  (B.  1911,  44,  1887,  2445, 
3272,  3279)  has  obtained  optically  active  derivatives  of  cobalt. 
It  is  pointed  out  that  compounds  like  CoA3BCD,  CoABC2D2 
or  CoABC4  should  exist  in  optically  active  isomerides,  pro- 
vided the  cobalt  atoms  occupy  the  centre  of  an  octahedron  and 
the  six  radicals  are  situated  at  the  solid  angles,  e.g.: 


Such  active  isomerides  have  been  isolated  in  the  case  of 
l-chloro(or  bromo)-2-ammine-diethylenediamine-cobaltic  salts, 
[CoBrNHgenJBr2,  where  C2  and  D2  are  replaced  by  divalent 
ethylenediamme  radicals  (NH2.CH2«CH2-NH2:).  The  reso- 
lution was  effected  by  means  of  <2-bromocamphorsulphonic  acid, 
and  the  active  salts  obtained  were  quite  stable.  Similar  cases 
of  isomerism  have  been  met  with  in  the  case  of  chromium 
derivatives  (Werner,  ibid.,  3132,  cf.  also  A.  386,  1).  For  stereo - 
isomeric  platinum-derivatives,  see  Kirmreuther,  B.  44,  3115. 

H.  Carbon  Compounds,  with  Semicyclic  Double  Linkings. 
— Many  years  ago  van't  Hoff  predicted  that  compounds  of  the 

allene   type,  ^>C:C:C<^f,  should   exist  in   optically  active 

modifications.  Attempts  by  Lapworth  and  Wechsler  (J.  C.  8. 
1910,  38)  to  obtain  such  compounds  in  optically  active  forms 
have  not  met  with  success.  Perkin  and  Pope  (J.  C.  S.  1906, 


fcOILING-POINT  636 

1075;  1909,  1789;  1911,  1510),  however,  have  succeeded  in 
resolving  l-methylcyclohexylidene-4-acetic  acid, 


into  optically  active  components  by  means  of  its  brucine  salt. 
The  two  forms  have  m.-pt.  52-5°-53°  and  [a]D  ±  81°  in  ethyl 
alcohol.  This  resolution  is  of  interest,  as  the  formula  does 
not  contain  an  asymmetric  carbon  atom,  although  the  mole- 
cule as  a  whole  is  asymmetric.  By  the  addition  of  bromine 
to  the  d-  and  Z-acids,  it  has  been  found  possible  to  obtain 
four  optically  active  dibromides. 

An  example  of  somewhat  the  same  type  is  met  with  in  the 
oxime  of  cyclohexan-l-one-4-carboxylic  acid, 


which  has  been  resolved  by  Mills  and  Bain  (J.  C.  S.  1910, 
1866)  into  active  forms  by  means  of  morphine  or  quinine. 
Two  active  sodium  salts  were  obtained,  but  when  acidified 
with  hydrochloric  acid  an  inactive  acid  was  formed. 

This  resolution  is  used  as  a  strong  argument  in  favour  of 
Hantzsch  and  Werner's  view  (p.  138)  that  when  a  tervalent 
nitrogen  atom  is  attached  by  a  double  linking  to  carbon  the 
three  valencies  of  the  nitrogen  do  not  lie  in.  a  single  plane. 
If  all  three  valencies  were  in  the  same  plane  the  formula  for 
the  oxime  would  contain  a  plane  of  symmetry  and  should 
not  be  resolvable. 

Azobenzene  (p.  396)  also  appears  to  exist  in  two  stereoiso- 
meric  forms  (G&rntner,  J.  A.  C.  S.  1910,  32,  1294),  viz.  red 
prisms,  m.-pt.  68°,  and  orange-red  needles,  m.-pt.  25°,  which 
are  represented  by  anti  and  syn  configurations. 


XLVII.  RELATIONSHIPS  BETWEEN  PHYSICAL  PRO- 
PERTIES AND  CHEMICAL  CONSTITUTION 

A.  Boiling-point.  —  Attention  has  been  repeatedly  drawn 
to  the  fact  that  in  any  homologous  series  the  boiling-point 
tends  to  increase  with  the  number  of  carbon  atoms  present 
(see  pp.  31,  66,  HI). 


636       XLVII.   PHYSICAL  PROPERTIES  AND   CONSTITUTION 

In  the  majority  of  cases  the  increase  in  boiling-point  for 
each  additional  CH2  is  not  constant,  but  tends  to  decrease 
with  increasing  molecular  weight  (e.g.  fatty  acids,  and  espe- 
cially the  paraffin  hydrocarbons  and  alkyl  haloids). 

In  the  case  of  the  ethyl  esters  of  the  normal  fatty  acids  the 


y  ac 
CH2 


increase  is  fairly  constant,  and  is  about  21°  for  a  CH2  group 
(Kopp,W2),W> 

Difference. 
Ethyl  formate  ................       54-5° 

Ethyl  acetate  .................       77°      _ 

Ethyl  propionate  ............       98° 

Ethyl  butyrate  ...............  120° 

Ethyl  valerate  ...............  144-5°  " 

Ethyl  hexoate  ................  167°  < 

Ethyl  heptoate  ...............  188°  *L 

Ethyl  octoate  .................  208°          *   ™0 

Ethyl  nonoate  ................  228° 

With  the  alkyl  chlorides  the  difference  between  methyl  and 
ethyl  chlorides  is  35°,  and  this  difference  diminishes  by  2°  for 
each  subsequent  homologue,  so  that  the  difference  between 
heptyl  and  octyl  chlorides  is  only  23°  (Schorlemmer). 

Attempts  have  been  made  to  find  a  general  law  for  the 
diminution  of  the  difference  in  boiling-point  with  increase  in 
molecular  complexity.  Goldstein  suggested  the  formula 


p  380  +  (n  -  1)  19  -  340-9° 

for  the  boiling-points  of  the  normal  hydrocarbons,  where  n  — 
the  number  of  carbon  atoms;  this  gives  good  results  up  to 
C12H26,  but  not  beyond.  (Compare  also  Mills,  Phil.  Mag.  [5], 
17,  180.) 

A  comparison  of  isomeric  substances  shows  that  the  boiling- 
points  can  vary  considerably,  even  when  the  isomerides  belong 
to  the  same  series,  e.g.  the  amyl  alcohols  : 

CH3(CH2)3.CH2.OH,  137°; 
(CH3)2CH.CH2.CH2.OH,  131-6°; 
CH3.CH2.CH(CH3).CH2.OH,  128*; 
CH3(CH2)2.CH(CH3)OH,  118-5°; 
CH3.CH2.CH(OH).CH2.CH3,  116'5°; 
(CH3)2CH-(CH3).OH,  112-5°. 

In  all  such  cases  the  normal  compound  has  the  highest 
boiling-point,  and  the  more  branched  the  carbon  chain 


BOILING-POINT  637 

becomes,  the  lower  is  the  boiling-point.  Generally  there  is  a 
difference  of  7°  between  the  boiling-points  of  a  pair  of  isomeric 
compounds  of  the  type  CH3 •  CH2 . CH2 . X  and  (CH3)2.CH.X. 
According  to  Menschutkin>  in  a  group  of  isomeric  alcohols, 
amines,  or  amides,  the  boiling-point  falls  as  the  side  chain 
approaches  the  hydroxy-  or  amino-substituent. 
A  comparison  of  isomeric  esters,  e.g. : 

n-Butyl  acetate,  CH3.(X).OC4H9,  124°; 
n-Propyl  propionate,  CH3.CH2.CO-O-C3Hr,  122'4°; 
Ethyl  rc-butyrate,  CH3.CH2.CH2.CO.O.C2H5,  121°; 
Methyl  n-valerate,  CH3.(CH2)3.CO.OCH3,  127°, 

shows  that  the  boiling-point  is  lower  the  nearer  the  oxygen 
atoms  are  to  the  middle  of  the  carbon  chain. 

A  remarkable  feature  is  the  relatively  high  boiling-points  of 
hydroxylic  compounds  when  compared  with  their  isomerides 
or  with  closely  related  compounds.  As  an  example,  the 
n  -acid  isomeric  with  the  last -mentioned  group  of  esters, 
namely  w-hexoic  acid,  boils  at  205°.  A  similar  relationship 
can  be  shown  by  the  comparison  of  an  alcohol  with  the  ethers 
isomeric  with  it.  Similarly,  a  comparison  of  the  boiling- 
points  of  the  ethyl-derivatives,  C2H6,  C2H5.OH,  C2H5C1, 
C2H5Br,  C2H5NH2,  C2H5.QEt,  C2H5.CN,  indicates  the  enor- 
mous effect  of  the  hydroxyl  group  on  the  boiling-point,  or, 
again,  a  comparison  of  the  boiling-point  of  an  acid  with  those 
of  its  chloride,  esters,  anhydride,  or  nitrile. 

The  effect  of  the  introduction  of  halogen  atoms  has  already 
been  referred  to  (p.  56).  The  introduction  of  an  atom  of 
chlorine  for  hydrogen  often  raises  the  boiling-point  some  60°, 
an  atom  of  bromine  about  84°,  and  an  atom  of  iodine  110°; 
and  the  introduction  of  a  second  or  third  chlorine  atom 
further  raises  the  boiling-point,  but  not  to  the  same  extent. 

Extremely  interesting  is  the  fact  that  a  saturated  compound 
and  its  ethylene  analogue  have  very  nearly  the  same  boiling- 
points  (cf.  propyl  and  allyl  alcohols,  both  97°;  G^H16  and 
CrH14,  both  99°;  propionic  acid,  1407°;  and  acrylic  acid,  140°), 
although  they  differ  considerably  as  regards  most  of  their 
other  physical  characteristics.  Further,  methyl  ketones, 
acetyl  esters,  and  corresponding  acid  chlorides  boil  at  very 
nearly  the  same  temperature,  e.g.  acetone,  methyl  acetate,  and 
acetyl  chloride  at  55°-56°;  propyl  methyl  ketone,  methyl 
butyrate,  and  butyryl  chloride  at  101°-105°  (Schroder,  B. 
1883,  16,  1312). 


638       XLVII.   PHYSICAL  PROPERTIES   AND  CONSTITUTION 

B.  Melting-point — Although,  on  the  whole,  in  any  homo- 
logous series  the  melting-points  of  the  solid  members  tend  to 
rise  with  increase  in  molecular  complexity,  in  many  series  an 
alternating  rise  and  fall  is  met  with,  the  members  containing 
an  even  number  of  carbon  atoms  melting  at  relatively  higher 
temperatures  than  those  with  an  odd  number.  This  is  the 
case  with  the  higher  fatty  acids,  as  is  readily  seen  when  the 
melting-points  are  plotted  against  the  number  of  carbon  atoms. 


40°- 

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No.  of  Carbon  Atoms 

Many  other  series  show  a  similar  relationship,  e.g.  succinic  acid 
and  its  homologues,  where  the  melting-points  are : 

C»  180°;  GO  97°;  C*  148°;  Cr,  103°;  C&  140°;  C9,  106°;  C10,  127°. 

(Compare  also  Beach,  Zeit.  phys.  1904,  50,  43.)  In  the  case 
of  a  group  of  closely  related  isomeric  compounds  it  is  found 
that  the  melting-point  tends  to  rise  with  the  number  of  side 
chains  or  branches,  e.g.  CH3«CH2«CH2.CH2«OH  is  a  liquid, 
and  C(CH3)3.OH  melts  at  25°;  or  again,  glutaric  acid  melts 
at  97°,  methyl-succinic  at  112°,  and  dimethyl-malonic  at  117°. 
The  conversion  of  an  acid  into  an  ester  always  produces  a 
lowering  of  the  melting-point,  and  the  methyl  ester  always 
has  the  highest  melting-point  of  any  of  the  esters  derived 
from  a  given  acid;  in  fact,  in  many  cases  the  methyl  esters 


MOLECULAR  VOLUME  639 

are  solids,  and  the  ethyl  and  higher  esters  liquids  at  the 
ordinary  temperature. 

In  the  aromatic  series  it  is  found  that  of  the  isomeric  0-, 
ra-,  and  ^-compounds  the  para-  has  the  highest  melting-point. 
G.  Schultz  (A.  1881,  207,  362)  has  also  shown  that  in  the 
group  of  compounds, 

Nitro  —  *•  azoxy  —  *•  azo  —  »•  hydrazo  —  »•  amine, 

the  melting-point  increases  up  to  the  azo-compound,  and  then 
falls  again  to  the  amine.  According  to  Franchimont  (Rec. 
1897,  16,  126),  the  melting-point  of  an  organic  compound  is 
invariably  raised  when  two  hydrogen  atoms  attached  to  the 
same  carbon  are  replaced  by  oxygen,  or  when  a  hydrogen 
atom  is  replaced  by  hydroxyl;  cf.  C6H5«CH2«OH  and  CJEL- 
CO-  OH,  or  C6H6  and  C6H5.QH. 

C.  Molecular  Volume.  —  The  relationships  between  specific 
gravity  and  chemical  constitution  are  not  so  marked  as  in  the 
case  of  other  physical  properties.  Attention  has  already  been 
drawn  to  the  fact  that  in  a  homologous  series  the  specific 
gravity  either  decreases  with  an  increase  in  the  number  of 
carbon  atoms,  and  tends  to  reach  a  minimum  value  (p.  141), 
or  increases  with  the  number  of  carbon  atoms  and  tends  to 
attain  a  maximum  (p.  31). 

More  interesting  results  have  been  obtained  by  an  exami- 

nation of  molecular  volumes,  i.e.  the  quantity  mo  e°u  ar  weig    t 

specific  gravity 

Kopp  (1842)  determined  the  molecular  volumes  of  a  number  of 
carbon  compounds,  and  came  to  the  conclusion  that  in  the 
case  of  closely  related  compounds  the  same  difference  in  com- 
position corresponds  with  a  similar  difference  in  molecular 
volume,  e.g.  : 

Mol.  volume.    Difference. 
Alcohols,         CHo-OH  ...............      42'2  on 

C2H6-OH  ...............       62-2  20 

C3H7.OH  ...............      81-34 

H  ...............     101-58  ~ 


Fatty  acids,     H.CO2H  ...............  41'4 

CH3.C02H  ............  63-7        ^  *** 

C2H5.C02H  ............  85-4            |{4 

C3Hr.C02H  ............  107-1 

and  further,  that  isomeric  liquids  have  the  same  molecular 
volumes,  e.g.  acetic  acid  63  -7,  and  methyl  formate  63  -4;  pro- 
pionic  acid  85-4,  ethyl  formate  85  -3,  and  methyl  acetate  84-8. 


640       XLVII.   PHYSICAL  PROPERTIES   AND   CONSTITUTION 

The  replacement  of  an  atom  of  oxygen  or  an  atom  of  carbon 
by  two  atoms  of  hydrogen  does  not  appear  to  alter  the  mole 
cular  volume  to  any  considerable  extent : 


Methyl  alcohol,  CH4O....     421 

Formic  acid,  CH2O2 41'4 

Benzy  1  alcohol,  C7H8O...   1237 


Amyl  alcohol,  C6H12O  ....    124'0 

Ether,  C4H10O 106-0 

Butyric  acid,  C4H8O2 107'1 


The  difference  due  to  a  CH2  group  is  roughly  22,  and  since 
the  atomic  volume  of  carbon  is  twice  the  atomic  volume  of 
hydrogen,  it  follows  that  the  atomic  volume  of  carbon  =11 
and  of  hydrogen  =  5*5.  Kopp  also  indicated  that  the  atomic 
volume  of  a  polyvalent  element,  e.g.  oxygen,  is  not  a  constant 
quantity,  but  varies  according  to  the  manner  in  which  the 
oxygen  atom  is  united  to  the  other  atoms  in  the  molecule. 

Thus  in  the  form  of  a  carbonyl  group,  ^>C:0,  the  atomic 
volume  of  oxygen  is  12  '2  (carbonyl  oxygen),  but  in  the  form 
of  ^C»0'C^  or  ^C»0«H  (oxidic  oxygen)  it  has  the  value 


7  '8.  Similarly,  Schiff  has  shown  that  the  carbon  atom  can 
have  different  values  according  as  it  is  united  to  another 
carbon  atom  by  a  single,  double,  or  triple  bond.  Thus  each 
double  bond  causes  an  increase  of  four  units  in  the  molecular 
volume.  By  means  of  these  atomic  volumes  it  is  possible  to 
calculate  the  molecular  volume  of  any  simple  carbon  com- 
pound, e.g.  ethyl  formate,  H-CO'O'CH^CHg, 

30      =  33   ^ 
6H     =  33    I         ™.n 
10:    =  12-2  f  =  860» 
l.Q.  =     7-8J 

and  the  value  actually  obtained  by  experiment  is  85-86. 
Although  such  generalizations  as  those  mentioned  are  of 
considerable  theoretical  importance,  the  method  is  not  one 
which  has  been  used  to  any  great  extent  for  determining 
the  constitution  of  chemical  compounds  (compare  molecular 
refraction  and  molecular  magnetic  rotation).  This  is  partly 
due  to  the  fact  that  the  specific  gravity,  and  hence  the  mole- 
cular volume,  varies  with  the  temperature.  At  first,  Kopp 
made  all  his  determinations  at  0°,  but  obtained  better  results 
by  taking  the  specific  gravity  at  the  boiling-point  of  the 
liquid.  It  is  not  necessary  to  actually  make  the  determin- 
ation at  the  boiling-point,  but  to  determine  the  specific  gravity 


MOLECULAR  REFRACTION  641 

at  a  lower  temperature,  and  then  to  correct  for  the  coefficient 
of  expansion  as  determined  by  the  dilatometer.  In  reality, 
the  determinations  should  be  made  at  temperatures  when  the 
liquids  are  all  in  an  exactly  comparable  condition,  viz.  at  the 
critical  point  (compare  Zeit.  phys.  1890,  6,  578).  More  recent 
determinations  of  molecular  volumes  by  T.  E.  Thorpe  (J.  C.  S. 
1880,  327)  indicate  that  isomeric  compounds  have  not  always 
the  same  molecular  volumes,  and  that  the  differences  amount 
to  several  units  per  cent,  but  that  elements  such  as  chlorine 
and  bromine  in  the  liquid  state  have  the  same  atomic  volumes 
as  in  their  organic  compounds  (compare  also  Lossen,  A.  1883, 
214, 138;  Horstmann,  B.  1885,  20,  766;  Sehi/,  A.  1884,  220,  71; 
Zahnder,  A.  1883,  214,  138). 

D.  Molecular  Refraction. — It  has  been  shown  that  the 
molecular  refraction,  like  the  molecular  volume,  is  to  a  large 
extent  an  additive  property,  i.e.  the  molecular  refraction  is 
the  sum  of  the  atomic  refractions  of  the  atoms  present  in  the 
molecule,  but,  in  addition,  that  it  is  to  a  certain  extent  consti- 
tutive; thus  the  oxygen  atom  has  distinct  atomic  refractions 
according  to  whether  it  is  in  the  carbonyl  or  oxidic  state  of 
combination. 

m,         r      ,.      .  j       .,    ir  sine  of  angle  of  incidence 

The  refractive  index  itself,  n  = , ^ — -. — ? : — , 

sine  of  angle  of  refraction 

does  not  lend  itself  to  the  study  of  generalizations,  but, 
according  to  Gladstone  and  Dale  (1858),  such  generalizations 

77  -       T 

are  found  when  the  specific  refractory  power,  — —  (where 

d  =  specific  gravity),  is  employed.  This  specific  refraction 
varies  but  little  with  the  temperature;  thus  with  water: 

t  o°  io"          20°          90°         100° 

Specific  refraction...     0'3338    0'3338    0'3336    0'3321     0'3323 

and  is  not  largely  affected  by  the  presence  of  other  substances. 
A  second  formula  for  the  specific  refractive  power  has  been 

o  i 

introduced  by  Lorentz  and  Lorenz,  viz.     n  ~  w;  this  has  the 

(TI   -f"  2)a 

advantage  that  the  value  appears  to  be  independent  of  the 
physical  state  of  the  compound: 

Lorentz- Lorenz  Gladstone- Dale 

t  Gas.         Liquid.  Gas.         Liquid. 

Water 10°    0*2068    0'2062        O'SlOl     0-3338 

Carbon  disulphide 10°    0'2898    0-2805        0*4347     0-4977 

Chloroform 10°    0'1796    01790        0'2694    0-3000 


642       XLVII.   PHYSICAL  PROPERTIES  AND  CONSTITUTION 

When  the  refractive  powers  of  different  substances  are  com- 
pared, it  is  usual  to  employ  the  molecular  refractive  powers 
rather  than  the  specific  refractions.  The  molecular  refraction 
is  the  product  of  the  specific  refraction  into  the  molecular 

weight;    according  to  Gladstone  —  ^n~"  ',  and  according  to 


As  the  refractive  index  differs  with  light  of  different  wave- 
lengths, it  is  necessary  to  determine  the  value  of  n  for  mono- 
chromatic light,  and  to  indicate  the  special  light  employed; 
generally  determinations  are  made  for  the  D  line  in  the 
sodium,  or  the  a  line  in  the  hydrogen  spectrum,  and  are 
carried  out  in  hollow  prisms  containing  the  liquid  and  pro- 
vided with  sides  of  plate  glass. 

Landolt  examined  the  molecular  refractions  of  the  members 
of  several  homologous  series,  and  came  to  the  conclusion  that 
the  molecular  refraction  is  an  additive  quantity,  and  that 
similar  changes  in  composition  induce  similar  changes  in  the 
molecular  refractive  power: 


Alcohols 

M(n-l) 

d  Diff. 

CH,-OH 13-17 


OH  ........     20-70 


—  7-53 

->  7-60 


Acids 


Diff. 


H-CO2H 13-91 

CH3.C02H 21-11 

C2H6-C02H 28-57 

C3H7.C02H 36-22 

44-05 


C3Hr.OH 28-30  _     ,_Q1 

C4H9.OH 36-11     *  Zji 

C6Hn.OH 43-38" 

and  similarly  for  various  groups  of  esters,  the  mean  value  for 
the  CH2  group  being  7 '6  units.  By  methods  similar  to  those 
described  under  molecular  volumes,  values  were  obtained  for 
the  atomic  refractive  powers  of  the  elements  for  the  a  line, 
e.g.  C  =  5,  H  =  1-3,  0  =  3,  Cl  =  9-79,  Br  =  15-34,  &c.  The 
values  thus  obtained  for  the  halogens  are  practically  identical 
with  those  determined  for  the  elements  in  the  free  state. 
The  molecular  refraction  of  any  simple  carbon  compound  can 
be  calculated  by  adding  together  the  atomic  refractions  of  the 
constituent  elements.  Thus,  for  ethyl  alcohol,  C2H60,  the 
calculated  molecular  refraction  is  2x5  +  6x1*3 +  3  =  2O8, 
and  that  actually  found  experimentally  is  20*7. 

According  to  Landolt,  the  molecular  refraction  is  purely 
additive,  and  thus  isomeric  compounds  should  possess  identical 
molecular  refractive  powers.  This  is  largely  true  in  certain 


MOLECULAR  REFRACTION  643 

cases,   e.g.   the   compounds   C3H603—  propionic   acid,"  28-57: 
methyl  acetate,  29-36;  and  ethyl  formate,  29-18. 

In  a  series  of  investigations  begun  in  1878  (A.  1879,  200, 
139;  1880,  203,  1  and  255)  Bruhl  has  examined  the  influence 
of  atomic  grouping  on  the  molecular  refraction,  and  has  been 
able  to  show  that  the  property  is  not  purely  additive,  but  to  a 
certain  extent  constitutive.  Thus  a  comparison  of  the  experi- 
mental and  calculated  values  for  unsaturated  and  the  corre- 
sponding saturated  compounds  at  once  exhibits  anomalies  : 


. 

for  a-line. 

Observed.     Calculated.  Difference. 
Allyl  alcohol,  C3H60  ............        27'88          25'8          2'08 

Propyl  alcohol,  C3H80  ..........         28'60          28'4          0'2 

Similarly  in  other  unsaturated  compounds  it  is  found  that  a 
double  bond  between  two  carbon  atoms  usually  increases  the 
molecular  refraction  by  about  two  units  (mean  value  2-15), 
and  a  triple  bond  by  T95  unit. 

Other  polyvalent  elements  have  atomic  refractions  which 
vary  with  their  state  of  combination;  thus  oxygen  in  carbonyl 
compounds  has  the  value  3-4  in  hydroxy-derivatives,  and  in 
ethers  the  value  2-8.  The  following  is  a  list  of  some  of  the 
more  important  atomic  refractions  used  by  Gladstone  and  by 
Bruhl: 

Briihl 
Gladstone.  (L.-L.  formula). 

Carbon  in  saturated  compounds  .........          5-0  2  -365 

Hydrogen  .....................................  1-3  T103 

Carbonyl  oxygen  in  ^>C:O  ...............          3'4  2*328 


Ether  oxygen  in      C-O-C     .............          2'8  1'655 

Hydroxylic  oxygen  in  ^C-O-H  ........          2*8  1-506 

Chlorine  .......................................          9'9  6'014 

Bromine  .......................................         15'3  8'863 

Iodine  .........................  .................        24*5  13'808 

Ethylenebond  ...............................          2'1  1'836 

Acetylene  bond  ..............................           T95  2'22 

Sulphur  in  C:S  ..............................        16'0 

Sulphur  in  C-S-H  ..........................        141 

Nitrogen  in  compounds  -^C  •  N<^  ......          ...  2'76 

Briihl  has  employed  the  molecular  refraction  for  the  investi- 
gation of  certain  tautomeric  substances,  e.g.  ethyl  acetoacetate, 


644      XLVII.   PHYSICAL  PROPERTIES  AND  CONSTITUTION 

The  observed  value  for  the  a  line  is  31*89,  and  the  values 
calculated  for  the  ketonic  and  enolic  formulae  respectively, 
31-53  and  32-55: 


CH3  •  CO  •  CH2  •  CO  •  OC2H5 
60  =  14-190 

10H  =  11-03 

2O  (carbonyl)  =     4'656 
10  (ether)         =     1'655 

31-531 


CH3  •  C(OH) :  CH  •  CO  •  OC2H5 
60  =  14-190 

1  ethylene  bond   =     1'836 
10H  =  11-03 

1O  (carbonyl)       =     2'328 
1O  (ether)  =     1-655 

lO(hydroxyl)      =     1-506 

32-545 


The  conclusion  to  be  drawn  from  these  numbers  is  that  the 
ethyl  acetoacetate  at  the  ordinary  temperature  consists  mainly 
of  the  ketonic  form,  but  probably  contains  a  small  amount 
of  the  enolic.  Bruhl  also  tests  the  purity  of  numerous  com- 
pounds prepared  by  him,  by  means  of  molecular  refraction  and 
dispersion  determinations  in  place  of  ordinary  combustions. 
Perkin  and  Gladstone  have  examined  the  molecular  refractive 
powers  of  several  di-  and  triketonic  substances.  Thus,  for 

acetylacetone  at  11°,  using  the  formula  ^—  M  for  the  a  line, 

the  value  45-17  was  obtained,  and  this  decreased  to  44*14  at 
99*3°.  The  ketonic  formula  requires  42*2,  the  mono-enolic 
43*7,  and  the  di-enolic  45-2.  At  11°  the  diketone  undoubtedly 
consists  mainly  of  the  dihydroxylic  compound  CH3«C(OH): 
C:C(OH)-CH3,  and  at  the  higher  temperature,  probably  of  a 
mixture  of  the  mono-  and  dihydroxylic  forms. 

Schaum  has  also  used  the  method  to  show  that  reagents  like 
sodic  ethoxide  or  piperidine  have  no  enolizing  or  ketonizing 
actions  on  ethyl  acetoacetate,  as  in  presence  of  both  these 
compounds  the  molecular  refraction  is  32  for  the  sodium  line 
Compounds  which  have  a  strong  dispersive  power  do  not 
appear  to  lend  themselves  to  the  calculation  of  molecular 
rotation  in  the  manner  just  described. 

E.  Molecular  Magnetic  Rotation, — This  is  quite  distinct 
from  the  ordinary  optical  activity  exhibited  by  substances 
with  asymmetric  molecules,  and  is  common  to  practically  all 
substances  when  they  are  examined  by  means  of  a  polarimeter 
in  a  strong  magnetic  field.  The  tube  containing  the  liquid  to 
be  examined  is  placed  end  on  between  the  two  poles  of  an 
electro-magnet,  these  poles  being  pierced  in  order  that  the  ob 


MOLECULAR  MAGNETIC  ROTATION  645 

server  may  take  readings,  and  the  apparatus  is  often  jacketed 
in  order  that  the  temperature  may  be  kept  constant.  (For 
new  form  of  apparatus,  see  J.  C.  S.  1906,  608.)  When  the 
magnetic  field  is  changed,  it  is  found  that  the  amount  of 
rotation  remains  the  same  but  changes  sign,  and  in  each 
determination  several  positive  and  several  negative  readings 
are  made.  The  rotations  of  all  substances  are  compared  with 
water  under  the  same  conditions,  and  thus  the  molecular 

magnetic  rotation  is  — — LJ,  where  M  is  the  molecular  weight 
Loa^d 

of  the  substance,  a  its  observed  rotation  using  a  column  of 
liquid  I  cm.  long,  and  d  the  specific  gravity  of  the  liquid; 
18  is  the  molecular  weight  of  water,  c^  its  observed  rotation, 
d1  its  density,  and  /x  the  length  of  column  used.  As  a  rule 
I  =  I-L  and  d-i  =  1  (approx.).  An  examination  of  different 
homologous  series  by  W.  H.  Perkin,  Sen.,  showed  that  for  an 
increase  of  CH2  in  the  molecule  there  is  usually  an  increase  of 
1-023  units  in  the  molecular  magnetic  rotation.  At  first, 
Perkin  attempted  to  obtain  atomic  magnetic  rotations  for  each 
element  in  the  same  manner  as  already  described  for  atomic 
volumes  and  atomic  refractions;  the  values  so  obtained  gave 
good  results  with  several  distinct  series,  but  could  not  be 
applied  generally.  The  method  of  using  series  constants  was 
then  adopted.  The  molecular  magnetic  rotation  r  of  a  com- 
pound may  be  represented  as: 

r  =  C  + 7i  1-023. 

Where  C  is  a  constant  which  varies  with  different  homolo- 
gous series,  n  is  the  number  of  carbon  atoms  present. 
A  few  of  the  constants  are : 


n-Parafnns 0'513 

wo-Paraffins 0-631 

n-  Alcohols 0-699 

iso-  Alcohols 0-844 

n- Fatty  acids 0'391 


Higher  esters 0'337 

Aldehydes 0'263 

Alkyl  chlorides 1'988 

Alkyl  bromides 3'816 

Alkyl  iodides 8-011 


Alkyl  acetates 0 '370 

If  in  any  series  it  is  required  to  calculate  the  molecular 
magnetic  rotation  of  a  member,  this  is  readily  accomplished 
by  adding  n  x  1'023  to  the  series  constant;  thus  for  ?i-nononic 
acid  we  have 

0-391  +  9  X  1-023  =  9-598, 

and  the  value  actually  found  by  experiment  is  9-600. 


646       XLVII,   PHYSICAL  PROPERTIES   AND  CONSTITUTION 

There  is  usually  a  definite  relationship  between  the  values 
for  an  unsaturated  compound  and  its  saturated  analogue,  e.g.: 


Diff. 


Ethyl  crotonate. . .    7 '589    ,  , ,  9 
Ethyl  butyrate....    6'477    J 


Diff. 


Ethyl  oleate 21-909    -,  ,,9 

Ethyl  stearate...    20797    J 


With  allyl  compounds  the  difference  is  not  so  great;  thus 
the  difference  between  allyl  alcohol,  4 -682,  and  propyl  alcohol, 
3 -768,  is  only  0-914,  and  similarly  for  other  allyl  compounds. 

These  facts  have  been  used  as  arguments  in  the  determina- 
tion of  the  constitution  of  undecylenic  acid  (J.  C.  S.  1886,  205). 
The  difference  in  molecular  magnetic  rotation  between  unde- 
cylenic acid,  C10H19'C02H,  and  undecylic  acid,  C^H^-COgH, 
is  0*897,  and  similarly  for  the  esters  the  difference  is  0"890.  It 
is  argued  that  this  difference  approximates  to  0*91,  the  usual 
difference  between  an  allyl  compound  and  the  corresponding 
saturated  derivative,  and  hence  undecylenic  acid  is  presumably 
an  allyl  derivative  with  the  formula  CH2 :  CH[CH2]8  -  C02H. 

The  molecular  magnetic  rotation  of  a  complex  compound  can 
be  calculated  by  taking  as  the  series  constant  the  mean  of  the 
series  constants  of  the  various  groups  of  compounds  which  it 
represents.  Thus  ethyl  lactate,  CH3.CH(OH)-C02C2H5,  pos- 
sesses the  groupings  characteristic  of  an  ethyl  ester  and  also  of 
a  secondary  alcohol;  the  series  constants  for  these  are: 

Ethyl  ester  =  0'337;  secondary  alcohol  =  0'844.     Mean  =  0'590. 

The  series  constant  for  ethyl  lactate  and  homologues  is  thus 
0-590,  and  the  molecular  magnetic  rotation  of  the  lactate 

5  X  1-023  -f  0-590  =  5'705, 

which  agrees  very  well  with  the  experimental  value,  5-720. 
The  values  of  their  molecular  magnetic  rotations  have  been 
used  by  Perlcin  in  discussions  on  the  constitutions  of  certain 
tautomeric  compounds,  especially  those  of  the  keto-enolic  type. 
In  the  case  of  ethyl  acetoacetate,  the  molecular  magnetic 
rotation  for  the  ketonic  form  may  be  calculated  as  follows: 

Series  constant  for  alkyl  acetate 0'370 

Series  constant  for  ketone 0'375 

Mean 0'372 

Molecular  rotation  =  6  X  T023  +  0'372  =  6-510. 
For  the  enolic  form— ethyl  /3-hydroxy-crotonate,  CH3«C(OH): 


ABSORPTION  SPECTRA  64? 

CH'C02C2H5 — the  molecular  rotation  may  be  calculated  by 
the  two  following  methods: 

1.  Molecular  rotation  of  ethyl  crotonate 7'589 

OH  replacing  H  as  in  alcohol 0'194 

Molecular  rotation  of  ethyl  hydroxy-crotonate 7 '783 

2.  Mol  ecular  rotation  for  ethyl  £-hydroxy-butyrate 6  '737 

Difference  between  unsaturated  and  corresponding  satu-)  1.110 

rated  compound / 

Molecular  rotation  for  ethyl  hydroxy-crotonate 7  '849 

The  experimental  value  actually  found  for  ethyl  acetoacetate 
at  the  ordinary  temperature  is  6 '501,  and  this  indicates  that, 
at  this  temperature,  the  ester  consists  essentially  of  the  keto- 
f orm.  Some  general  conclusions  drawn  by  Perkin.  are : — 

(i)  That  monoketonic  compounds  and  keto- esters,  which 
react  as  tautomeric  substances,  as  a  rule,  have  the  ketonic  and 
not  the  enolic  structure,  except  when  a  number  of  negative 
groups,  such  as  phenyl  and  car  boxethyl,  •  C02C2H5,  are  present. 
These  have  an  enolizing  tendency,  as  shown  in  ethyl  benzoyl- 
acetate,  C6H5  •  CO  •  CH2  •  C02C2H5,  which,  according  to  Perkin, 
is  a  mixture  of  some  75  per  cent  of  the  keto-  and  25  per  cent 
enolic  compound. 

(ii)  Acetylacetone  at  17°  consists  of  a  mixture  of  some 
80  per  cent  of  the  hydroxy-ketone,  CH3-CO.CH:C(OH).CH3, 
and  some  20  per  cent  of  the  dienolic  form,  CH3»C(OH):C: 
C(OH)»CH3.  If  alkyl  radicals  replace  the  hydrogen  atoms 
of  the  methylene  group  of  acetylacetone,  the  tendency  to  form 
the  enolic  form  is  less  marked,  whereas  the  introduction  of 
negative  groups,  'COgEt,  increases  the  tendency. 

(iii)  Rise  of  temperature  favours  ketonization. 

(For  full  details,  see  J.  C.  S.  1884,  421;  1886,  205,  777; 
1887,  362,  808;  1888,  561,  695;  1889,  680;  1891,  981;  1892, 
800;  1893,488;  1894,402,815;  1895,255;  1896,1025;  1900, 
267;  1902,  177,  292.) 

F.  Absorption  Spectra.— Ostwald  (Zeit.  phys.  1892,  9,  579) 
has  studied  the  absorption  spectra  of  groups  of  closely  related 
coloured  compounds,  e.g.  a  series  of  soluble  metallic  perman- 
ganates, various  salts  of  fluorescein,  eosin,  and  rosolic  acid,  and 
has  been  able  to  show  that,  in  dilute  solutions,  the  absorption 
spectrum  of  a  salt  is  the  sum  of  the  spectra  of  the  ions;  thus 
all  the  permanganates  gave  practically  the  same  absorption 

due  to  the  Mn208  ion. 


648       XLVIL   PHYSICAL  PROPERTIES  AND   CONSTITUTION 

Hartley  and  others  have  carried  out  numerous  investigations 
on  ultra-violet  absorption  spectra  of  carbon  compounds,  and 
extremely  important  relationships  have  been  established. 
(For  references,  see  B.  A.  Reports  mentioned  in  Preface.) 
Hartley  photographed  the  spark  spectrum  of  an  alloy  of  tin, 
lead,  cadmium,  and  bismuth  after  it  had  passed  through  a 
solution  of  the  substance  under  examination.  It  was  found 
that  practically  all  open-chain  and  even  the  closed-chain  poly- 
methylene  compounds  give  no  distinct  selective  absorption; 
they  are  remarkably  transparent  to  ultra-violet  rays. 
Numerous  exceptions,  e.g.  ethyl  acetoacetate  derivatives, 
ke tones,  and  practically  all  ketonic  compounds,  whether  open- 
chain  or  cyclic,  have  since  been  met  with  (Baly  and  Desch, 
J.  C.  S.  1904,  1039).  In  any  given  series,  e.g.  the  alcohols,  it 
is  usually  found  that  each  increment  of  CH2  produces  a  slight 
increase  in  the  absorption  of  the  more  refrangible  rays. 

Benzene  derivatives,  naphthalene,  anthracene,  phenanthrene, 
and  their  derivatives,  also  pyridine,  quinoline,  dimethylpyrazin, 

N^QjjfQ-jyj-^N,  in  alcoholic  or  aqueous  solutions,  exhibit,  in 

many  cases,  distinct  absorption  bands.  Most  of  the  terpenes, 
furane,  thiophene  and  pyrrole  derivatives,  piperidene  and  re- 
duced benzene  derivatives,  resemble  the  aliphatic  compounds. 

In  all  cases  Hartley  examined  the  absorption  for  solutions  of 
very  different  concentrations,  always  increasing  the  dilution 
until  complete  transmission  was  obtained.  He  also  used  layers 
of  the  given  solutions  of  different  lengths,  and  then  plotted  the 
results  in  the  form  of  curves,  putting  the  oscillation  frequencies 
(reciprocal  of  wave-lengths)  as  abscissae,  and  equivalent  thick- 
nesses of  solution  as  ordinates.  Thus  with  two  solutions,  one 
•01 N  and  the  second  -001 N,  and  using  layers  of  each  30,  20, 
15,  10,  5  mm.  thick,  the  equivalent  thicknesses  are  300,  200, 
150,  100,  50,  30,  20,  15,  10,  and  5,  and  these  numbers  are  used 
in  the  plotting.  Baly  and  Desch  have  used  the  iron  arc  spectrum 
and  a  glass  cell  with  quartz  ends  for  containing  the  solution, 
so  arranged  that  the  length  of  the  column  of  liquid  can  easily 
be  varied.  They  also  plot  the  oscillation  frequencies  against 
the  logarithms  of  the  relative  thicknesses  of  liquid.  It  is 
claimed  that  from  the  absorption  curves  so  plotted  it  is 
very  much  easier  to  compare  the  relative  persistence  of  the 
absorption  bands. 

Hartley  examined  a  number  of  isomeric  benzene  derivatives, 
e.g.  xylenes,  cresols,  and  dihydroxy-benzenes,  and  found  that 


ABSORPTION  SPECTRA  649 

the  oscillation  frequency  of  the  extreme  rays  transmitted 
follows  the  order  ortho  —  *  meta  —  >  para,  i.e.  the  para-com- 
pounds exhibit  the  greatest  absorption.  The  same  generaliza- 
tion does  not  hold  for  other  groups  of  compounds,  e.g.  the 
hydroxy-benzoic  acids. 

A  most  important  fact  is  that  the  introduction  of  a  methyl 
group  for  a  hydrogen  atom  affects  the  absorption  spectrum 
but  little;  as  a  rule,  it  slightly  increases  the  general  absorption, 
but  does  not  alter  the  general  character  of  the  spectrum,  e.g. 
benzene  and  toluene,  benzoic  acid  and  methyl  benzoate. 

This  fact  has  been  largely  used  by  Hartley  and  Dobbie  in 
discussions  on  the  constitution  of  certain  tautomeric  substances, 
more  especially  those  of  the  lactam-lactim  type.  A  study  of 
the  general  chemical  properties  of  isatin  (p.  523)  does  not 
render  it  possible  to  say  whether  this  compound  has  the 
lactam  constitution  I,  or  the  lactim  constitution  II: 

I  C6H4<™>00  II  C6H4<*g>C.OH. 

Isatin  gives  rise  to  the  two  distinct  methyl  ethers  :  (a)  methyl- 
isatin,  III,  a  solid  melting  at  101°,  readily  hydrolysed,  and 
obtained  by  the  action  of  methyl  iodide  on  silver  isatin; 
(b)  pseudo-  methyl  -isatin,  IV,  a  solid  melting  at  134°,  not 
readily  hydrolysed,  and  prepared  by  heating  methyl-dibromo- 
oxindole  with  water: 


III  CHC.OCH  IV 


An  examination  of  the  absorption  curves  of  the  three  com- 
pounds, isatin,  methyl-isatin,  and  pseudo-methyl-isatin  (J.  C.  S. 
1899,  640),  shows  that  the  curves  for  isatin  and  the  pseudo- 
ether  are  practically  identical,  both  possessing  two  bands  of 
similar  intensity  and  differing  considerably  from  that  of 
methyl-isatin,  which  consists  of  a  single  band.  There  can  be 
no  question  but  that  isatin  itself  has  a  constitution  similar 
to  that  of  the  pseudo-methyl  ether;  and  since  the  reactions 
of  this  prove  beyond  doubt  that  it  is  a  nitrogen  and  not  an 
oxygen  ether,  isatin  must  have  the  lactam  constitution  repre- 
sented by  formula  I.  Similarly  carbostyril  (p.  541),  by  a  com- 
parison of  its  absorption  curve  with  that  of  its  two  methyl 
ethers,  can  be  shown  to  possess  the  lactam  constitution  I  and 
not  the  lactim  constitution  II  : 


650      XLVII.   PHYSICAL  PROPERTIES  AND  CONSTITUTION 

and  o-oxycarbanil,  obtained  by  fusing  o-amino-phenol  hydro- 
chloride  with  carbamide,  has  an  absorption  spectrum  practi- 
cally identical  with  that  of  its  N-ethyl  ether,  and  hence  has 

the  lactam  constitution  C6H4<Q^>CO. 

Hartley  and  DdbUe  (J.  C.  S.  1900,  498)  have  also  examined 
the  absorption  spectra  of  the  three  dibenzoyl-succinates  ob- 
tained by  Knorr.  According  to  the  latter,  the  a-compound  has 
the  enolic  constitution  I,  whereas  the  two  solid  /3-  and  y-com- 
pounds  are  stereo-isomeric  ketones  with  constitution  II : 

OH  •  CPh :  C  •  CO2Et  COPh  -  CH .  CO2Et 

1  OH.CPh:C-CO2Et  l  COPh •  CH •  002Et 

In  accord  with  this  view  is  the  fact  that  the  /3-  and  y-com- 
pounds  give  practically  the  same  spectrum,  which  differs,  how- 
ever, considerably  from  that  of  the  a-compound.  The  trans- 
formation of  the  a-  into  a  mixture  of  the  /?-  and  y-compounds 
can  readily  be  followed  by  examining  alcoholic  solutions  at 
different  intervals  of  time;  at  the  end  of  three  hours,  consider- 
able change  has  taken  place,  and  at  the  end  of  three  weeks  the 
ketonization  is  practically  complete. 

Baly  and  Descli  have  found  that  although  ethyl  aceto- 
acetate  in  dilute  solution,  and  its  two  ethyl  derivatives, 
CH3.CO.CHEt.C02Et  and  CH3 . C(OEt) : CH . C02Et,  give  no 
selective  but  only  general  absorption,  the  metallic  derivatives, 
e.g.  ethyl  sodio-acetoacetate,  have  distinct  banded  absorption 
spectra,  and  that  even  the  addition  of  a  small  amount  of  alkali 
to  ethyl  acetoacetate  produces  a  banded  spectrum.  Acetyl- 
acetone  itself  and  its  aluminium,  beryllium,  and  thorium  deri- 
vatives all  give  banded  ultra-violet  absorption  spectra.  Since 
neither  the  C-  nor  the  0-ethyl  derivative  of  ethyl  acetoacetate 
produces  selective  absorption,  it  would  appear  that  the  char- 
acteristic band  in  open -chain  compounds  cannot  be  due  to 
either  the  ketonic  or  the  enolic  constitution,  and  Baly  and 
Desch  draw  the  conclusion  that  these  absorption  bands  are 
only  produced  by  compounds  which  are  in  an  actual  state  of 
change,  for  example,  passing  alternately  from  the  ketonic  to 
the  enolic  form;  in  all  cases  valency  changes  (desmotropism), 
and  in  particular  cases,  e.g.  keto-enolic  compounds,  a  wander- 
ing of  a  labile  atom  (tautomerism)  occur.  Within  certain 
limits  the  same  type  of  valency  change  produces  an  ultra- 
violet absorption  band  in  the  same  position,  although  the 


ABSORPTION  SPECTRA  651 

compounds  undergoing  change  may  contain  elements  of  very 
different  atomic  weights,  e.g.  hydrogen,  sodium,  aluminium, 
thorium;  the  vibrations  in  the  molecule  which  synchronize 
with  the  oscillation  frequency  of  the  rays  absorbed  cannot, 
therefore,  be  the  vibration  of  the  labile  atoms  themselves,  but 
may  be  due  to  the  change  of  linking  (J.  C.  S.  1905,  768), 
i.e.  according  to  the  electronic  theory  to  the  vibrations  of  the 
valency  electrons.  The  persistence  of  the  band  over  a  definite 
range  of  concentration  is  taken  as  a  measure  of  the  relative 
number  of  molecules  which  are  actually  undergoing  change. 

The  absorption  bands  characteristic  of  simple  benzene  deri- 
vatives may  be  accounted  for  in  a  somewhat  similar  manner 
(J.  C.  S.  1904,  1029;  1905,  1331).  In  the  case  of  simple 
benzene  derivatives,  especially  hydrocarbons,  seven  distinct 
bands  are  visible,  due  to  seven  distinct  valency  changes. 
(Compare  also  J.  C.  S.  1906,  514,  983;  1907,  449,  1122;  1908, 
1906;  1910,  571,  1337,  1494.) 

Baly  and  Stewart  (ibid.  1906,  489,  502,  618)  have  examined 
the  absorption  curves  of  various  ketones  and  quinones.  Their 
results  with  fairly  concentrated  solutions  show  that  the  ketones 
which  show  the  most  persistent  absorption  bands  are  those 
which  are  most  reactive  from  a  chemical  point  of  view,  e.g. 
react  most  readily  with  sodium  hydrogen  sulphite  or  with 
hydroxylamine.  In  these  cases  also,  the  bands  are  attributed 
to  actual  valency  changes  (desmotropism)  going  on  in  the 
molecules  of  the  substances.  With  /3-diketones  and  mono- 
ketones  the  change  is  between  the  keto-  and  enolic  forms. 

It  is  well  known  that  the  entrance  of  substituents  into  the 
acetone  molecule  tends  to  diminish  its  reactivity,  a  pheno- 
menon which  for  several  years  has  been  attributed  to  steric 
hindrance  (pp.  175,  449).  Baly  and  Stewart  object  to  this 
view,  since  it  does  not  account  for  the  increased  reactivity  of 
ethyl  acetoacetate  as  compared  with  acetone,  or  more  especially 
with  methylethyl  ketone.  The  relative  reactivities  of  the 
three  compounds  are  indicated  by  the  following  numbers: 
Methylethyl  ketone,  22*5;  acetone,  39 '7;  ethyl  acetoacetate, 
47 '0,  which  give  the  percentage  amount  of  each  compound 
transformed  into  its  bisulphite  derivative  after  twenty  minutes. 

The  ordinary  theory  of  steric  hindrance  would  lead  us  to 
expect  that  ethyl  acetoacetate  would  be  less  reactive  than 
acetone,  since  it  contains  the  relatively  large  substituent 
•  C02Et.  Since  ketones,  when  arranged  according  to  their 
reactivities,  and  according  to  the  persistence  of  their  absorp- 


652       XLVII.   PHYSICAL  PROPERTIES  AND  CONSTITUTION 

tion  bands,  follow  the  same  order,  there  would  appear  to  be 
a  simple  relationship  between  the  two  properties;  and  accord- 
ing to  Baly  and  Stewart  both  are  due  to  the  same  cause, 
namely,  the  extent  to  which  tautomeric  or  desmotropic  change 
occurs  in  the  molecule.  In  the  case  of  the  keto-enolic  com- 
pounds, 

R.CO.CH2R'  z±  E.C(OH):CHK', 

the  carbonyl  group  is  supposed  to  be  in  a  specially  reactive 
state  during  the  change  —  in  fact,  to  be  in  a  condition  com- 
parable with  what  is  usually  termed  the  nascent  state  in  the 
case  of  the  elements.  The  introduction  of  substituents,  as  a 
rule,  lessens  the  amount  of  tautomeric  change  occurring  in  the 
molecule,  and  thus  lessens  its  chemical  reactivity.  The  intro- 
duction of  the  carbethoxy-group,  however,  tends  to  increase 
the  desmotropism,  as  is  shown  by  a  comparison  of  the  absorp- 
tion curves  of  concentrated  solutions  of  acetone  and  of  ethyl 
acetoacetate,  and  thus  the  chemical  activity  of  the  ketone  is 
increased  and  not  diminished  by  the  introduction  of  the 
•  C02Et  group. 

The  enormous  reactivity  of  ethyl  pyruvate  and  its  very 
persistent  absorption  bands  are  accounted  for  by  a  dynamic 
change  of  the  type 

CHg-C-C-OEt        ^    CH3.C:C.OEt 

oo  6-6 

Quinones  also  give  characteristic  absorption  bands  which 
are  attributed  to  the  change: 

/CH  :  CH\ 
(5.0  --  0-C    =± 


The  introduction  of  substituents  into  the  quinone  molecule 
renders  the  absorption  bands  less  persistent,  and  also  lessens 
the  chemical  reactivity  of  the  compound. 

An  examination  of  the  absorption  curves  of  the  nitranilines, 
where  there  are  persistent  bands  in  the  visible  part  of  the 
spectrum  closely  resembling  those  of  quinone,  leads  Baly, 
Edwards,  and  Stewart  (J.  C.  S.  1906,  513)  to  the  conclusion 
that  the  free  amines  have  a  quinonoid  structure, 


ABSORPTION   SPECTRA  653 

and  that  tautomeric  change  of  the  same  type  as  that  de- 
scribed under  the  quinones  occurs.  Their  hydrochlorides,  on 
the  other  hand,  have  the  ordinary  benzenoid  constitution, 
N02.C6H4.NH2,  HC1. 

The  nitro-phenols  give  absorption  spectra  which  closely 
resemble  those  of  their  methyl  ethers,  and  would  appear  to 
have  the  benzenoid  formula  N02«C6H4.OH.  The  sodium 
salts,  on  the  other  hand,  give  absorption  curves  which  closely 
resemble  those  for  the  nitranilines,  and  would  thus  be  repre- 
sented by  the  quinoid  formula, 


which  would  be  capable  of  tautomeric  change  in  much  the 
same  manner  as  quinone. 

According  to  Lomy  and  Desch  (J.  C.  S.  1909,  807),  intra- 
molecular change  is  not  always  accompanied  by  selective 
absorption.  The  conversion  of  normal  nitrocamphor  into  the 
pseudo-isomeride,  a  reaction  which  can  be  studied  quanti- 
tatively (p.  657),  is  not  accompanied  by  any  characteristic 
absorption  bands,  but  such  bands  make  their  appearance  when 
an  alkali  is  added,  and  the  addition  of  an  excess  of  alkali  does 
not  produce  increased  absorption.  The  absorption  cannot  be 
due  to  tautomeric  change,  as  in  the  presence  of  the  alkali  the 
nitrocamphor  exists  as  a  stable  sodium  salt.  The  following 
formulae  are  suggested  (where  X  =  C8H14)  : 

,Q 

CH.N02  yO<-    ^ 

Normal,  X-  ;    pseudo,  X<.     N-C'H. 


yC:NO.ONa 
sodium  salt,  X<^  • 

Hantzsch  (B.  43,  1549),  as  the  result  of  spectroscopic  investi- 
gations of  ethyl  acetoacetate  and  its  derivatives,  draws  the 
conclusion  that  the  specific  absorption  observed  in  solutions 
cannot  be  due  to  the  enolic  modification,  nor  yet  to  an  oscil- 
lation between  the  ketonic  and  enolic  states,  but  to  an  iso- 
meric  aci-form  in  which  the  latent  valencies  of  two  oxygen 
atoms  are  operative,  e.g.  : 

CH3.C.OH 

H-C-eb-OEt. 
The  fact  that  an  increase  in  the  amount  of  alkali  produces  an 


654       XLVII.   PHYSICAL  PROPERTIES  AND  CONSTITUTION 

increase  in  the  selective  absorption  is  attributed  to  the  fact 
that  an  excess  of  alkali  prevents  the  hydrolysis  of  the  sodium 
salt  to  the  enol  and  sodium  hydroxide. 

The  absorption  bands  of  various  vapours,  e.g.  benzene,  py- 
ridine,  furane,  and  thiophene  derivatives,  have  been  studied  by 
Hartley  (Phil.  Trans.  1908,  A.  208,  475)  and  Purvis  (J.  C.  S. 
1910,  692,  1035,  1546,  1648;  1911,  2318),  who  show  that  in 
the  form  of  vapour  these  compounds  give  absorption  spectra 
which  are  much  more  complex  than  those  of  their  solutions. 

The  conclusion  that  ethyl  acetoacetate  is  an  equilibrium 
mixture  of  the  ketonic  and  enolic  modifications — a  conclusion 
based  mainly  on  the  study  of  physical  properties — has  been 
confirmed  quite  recently  by  other  methods.  Of  these,  the 
following  are  the  more  important: 

1.  Kn&rr  (B.  1911,  44,  1138)  has  shown  that,  by  cooling  to 

—  78°  a  solution  of  the  ordinary  ester  in  alcohol  and  ether 
in  an  apparatus  specially  designed  to  exclude  moisture  and  to 
maintain  a  high  vacuum,  the  ketonic  form  separates  as  well- 
defined  needles  or  prisms,  m.-pt.  —  39°  and  b.-pt.  39°-40°/  2  mm. 
It  does  not  give  a  coloration  with  ferric  chloride,  and  does  not 
react  with  bromine  solution.     Even  at  the  ordinary  tempera- 
ture it  takes  several  weeks  before  the  equilibrium  mixture  is 
again  formed.     The  practically  pure  enol  is  obtained  by  sus- 
pending the  sodium  derivative  in  light  petroleum  cooled  to 

—  78°  in  a  special  apparatus,  and  passing  in  hydrogen  chloride 
just  insufficient  for  complete  decomposition.      The  solution 
when  filtered  and  evaporated  at  —78°  yields  the  enolic  ester 
as  a  colourless  oil,  which  gives  an  intense  coloration  with  ferric 
chloride.    At  the  ordinary  temperature  it  requires  ten  to  four- 
teen days  to  again  form  the  equilibrium  mixture,  but  at  100° 
the  change  is  completed  in  one  minute.     By  comparing  the 
refractive  index  of  the  ordinary  ester  with  the  values  for 
mixtures  of  known  concentration,  it  has  been  calculated  that 
the  equilibrium  mixture  contains  2  per  cent  of  the  enol. 

2.  By  means  of  experiments  made  with  compounds  which 
exist  in  stable  keto  and  enolic  forms,  K.  H.  Meyer  (A.  380, 
212;   B.  44,  2718)  shows  that  the   unsaturated  hydroxylic 
modification  reacts  instantaneously  with  an  alcoholic  solution 
of  bromine,  yielding  an  unstable  dibromide,  which  immediately 
gives  off  hydrogen  bromide  and  forms  the  bromo  -  ketone. 
The  best  method  for  estimating  the  amount  of  enol  is  to  add 
an  excess  of  the  alcoholic  bromine  solution,  to  remove  the 
excess  by  means  of  /3-naphthol,  and  then  to  determine  the 


ANOMALOUS   ELECTRIC  ABSORPTION  655 

amount  of  bromo-ketone  by  adding  potassium  iodide  solution, 
and  titrating  the  liberated  iodine  by  means  of  standard  thio- 
sulphate : 

— CO-CHBr—    — *    —  CI(OH).CHBr— 

—   — CI(OH).CHI —  C(OH):CH  +  L, 

In  this  way  it  has  been  shown  that  the  ordinary  ethyl  aceto- 
acetate  contains  about  7  per  cent  of  the  enol,  and  the  same 
results  are  obtained  when  freshly  prepared  solutions  in  various 
solvents  are  examined;  but  such  solutions  when  kept  undergo 
change,  e.g.  a  hexane  solution  when  kept  for  forty-eight  hours 
at  18°  contains  nearly  equal  amounts  of  keto  and  enolic  modi- 
fications. A  rise  in  temperature  also  tends  to  favour  the 
formation  of  the  ketonic  form.  In  a  similar  manner  acetyl- 
acetone  has  been  shown  to  contain  80  per  cent  of  enol. 

3.  Knorr  and  Schubert  (B.  1911,  44,  2772)  use  a  colori- 
metric  method  for  estimating  enols  in  allelotropic  mixtures, 
a  method  which  is  based  on  the  reaction  between  the  enol 
and  ferric  chloride, 

EH  +  FeCl3  =  FeRCl2  +  HC1, 

where  R  is  the  enolic  residue.  The  comparison  is  made  with 
standard  solutions  prepared  by  mixing  solutions  of  the  pure 
enol  with  one  of  sublimed  ferric  chloride  in  molecular  pro- 
portions. 

G.  Anomalous  Electric  Absorption. — P.  Drude  (B.  1897,  30, 
941)  has  found  that  numerous  organic  compounds  containing 
hydroxyl  groups  are  capable  of  absorbing  electric  waves  of 
high  frequency  (about  400  million  per  second),  although  they 
are  not  good  conductors;  whereas  ordinary  non-conductors 
show  no  such  absorption.  The  phenomenon  is  termed  by 
Drude  "anomalous  electric  absorption",  and,  with  the  ex- 
ception of  water,  all  liquid  hydroxyl  derivatives  display  this 
anomalous  absorption.  The  presence  of  hydroxyl  groups 
cannot  always  be  inferred  from  the  exhibition  of  anomalous 
absorption,  as  a  few  compounds  which  contain  no  hydroxyl 
groups  possess  the  property  to  a  slight  extent. 

Drude  himself  applied  the  method  to  the  examination  of 
certain  keto-enolic  tautomeric  substances.  Ethyl  acetoacetate 
itself  absorbs  but  slightly,  and  is  thus  presumably  mainly  the 
keto-form. 

Ethyl  benzoylacetate  and  ethyl  oxalacetate  absorb  strongly, 
and  should  thus  contain  considerable  percentages  of  the  enols. 


656       XLVII.    PHYSICAL   PROPERTIES   AND   CONSTITUTION 

H.  Optical  Activity.  —  Attention  has  already  been  drawn  t" 
the  fact  that  compounds,  the  molecules  of  which  are  asym- 
metric, are,  when  in  the  liquid  or  dissolved  state,  optically 
active,  i.e.  able  to  rotate  the  plane  of  polarization  (p.  154) 
either  to  the  right  (dextro-rotatory)  or  to  the  left  (Isevo- 
rotatory).  The  specific  rotatory  power  [a]  of  a  liquid  is 
obtained  by  dividing  the  observed  rotation  by  the  length  of 
the  column  of  liquid  used  and  by  the  specific  gravity  of  the 

liquid  [a]  =  -  —  -,  and  the  molecular  rotation  is  the  product 

of  the  specific  rotatory  power  into  the  molecular  weight  (M). 
For  a  solution  : 


ra]  =   1QQa  —       IQOa       _   IQOa  X  v 
lXc  ~ 


where  c  =  concentration  or  number  of  grams  of  the  active 
compound  in  100  c.c.  of  solution,  d  =  specific  gravity  of  the 
solution,  p  =  per  cent  of  active  substance  in  the  solution,  and 
g  =  number  of  grams  of  active  substance  in  v  c.c.  of  solution. 
The  specific  rotatory  power  of  a  solution  may  often  be  in- 
creased enormously  by  the  introduction  of  an  inorganic  salt; 
some  of  the  most  effective  are  boric  acid  and  alkali  molybdates 
and  tungstates.  As  a  rule,  the  nature  of  the  monochromatic 
light,  e.g.  sodium  light,  is  indicated,  also  the  temperature  and 
the  nature  of  the  solvent,  e.g.  [a]1^,  where  D  indicates  that  the 
number  refers  to  sodium  light  and  that  the  determination  was 
made  at  15°.  Various  attempts  have  been  made  to  deduce 
general  conclusions  bearing  upon  the  amount  of  rotation  and 
the  constitution  of  the  compound.  Guye  (C.  R.  110,  714)  has 
attempted  to  connect  the  degree  of  asymmetry  of  the  molecule 
of  a  compound  C  a,  b,  c,  d  with  the  masses  of  the  four  radicals 
present  and  the  distance  of  the  centre  of  gravity  of  the  mole- 
cules from  the  centre  of  the  tetrahedron  (C.  E.  1896,  1309; 
1898,  181,  307).  The  researches  of  P.  F.FranEand  and  others 
(J.  C.  S.  1899,  337,  347,  493,  &c.)  have  shown  that  Guye's 
conclusions  are  not  of  general  application. 

Patterson  (J.  C.  S.  1901,  167,  477;  1902,  1097,  1134;  1904, 
765,  1116,  1153;  1905,  122,  313)  has  made  a  careful  investi- 
gation of  the  influence  of  solvent,  temperature,  &c.,  on  the 
optical  activity  of  various  substances.  He  finds  that  dilute 
solutions  of  ethyl  tartrate  in  water,  or  in  methyl,  ethyl,  or 
propyl  alcohol,  possess  a  higher  specific  rotation  than  the  pure 
ester  itself,  that  the  specific  rotation  increases  with  dilution 


OPTICAL  ACTIVITY  657 

until  a  concentration  of  10  grams  in  100  grams  of  solvent  is 
reached,  and  then  the  rotation  remains  practically  constant. 
The  highest  values  are  always  obtained  with  aqueous  solutions, 
and  the  other  solutions  follow  in  the  order  —  methyl,  ethyl, 
Ti-propyl,  isobutyl,  and  sec-octyl  alcohol. 

The  effect  of  increase  of  temperature  upon  corresponding 
solutions  varies  somewhat.  In  water  the  coefficient  is  nega- 
tive for  dilute  solutions,  but  in  the  various  alcoholic  solutions 
it  is  positive,  as  it  is  also  for  the  pure  ester. 

According  to  Patterson  the  change  in  specific  rotation  with 
solvent  or  temperature  is  not  to  be  attributed  to  association, 
but  rather  to  the  internal  pressure  of  the  solvents  (compare 
Abst.  1900,  2,  329). 

Walden  has  also  conducted  numerous  investigations  on  opti- 
cally active  compounds,  and  concludes  that  there  is  a  relation- 
ship of  a  qualitative  nature  only  between  the  optical  activity 
of  a  substance  in  a  given  solution  and  its  molecular  weight  in  . 
that  solution.  (For  a  summary  of  work  on  optical  activity  see 
Walden,  B.  1905,  38,  345-409). 

The  polarimetric  method  has  been  used  by  Lowry  (J.  C.  S. 
1899,  75,  211)  for  a  quantitative  study  of  the  tautomerism  or 
dynamic  isomerism  of  the  nitro-  and  bromo-nitro-camphors. 

Each  of  these  compounds  appears  to  exist  in  two  distinct 


forms,  one  of  which  contains  the  nitro-group,  >CH»N^Q,  and 
the  other  the  isonitro-group,  ^>C:NO'OH.  Ordinary  crystal- 

line nitro-camphor,  melting  at  102°,  is  regarded  as  consisting 
of  the  normal  form,  its  homogeneity  being  vouched  for  by  the 
constancy  of  its  initial  specific  rotatory  power  ([a]D  =  —124° 
in  5-per-cent  benzene  solution),  and  by  its  well-defined  crystal- 
line form.  When  dissolved  the  nitro-compound  at  once  begins 
to  change  into  the  pseudo  form,  and  this  change  is  accompanied 
by  an  alteration  in  the  rotatory  power;  with  the  5-per-cent 
benzene  solution  the  specific  rotatory  power  has  fallen  to 
—  104°  at  the  end  of  four  days,  and  then  remains  stationary. 
This  solution  represents  a  mixture  of  the  normal  and  pseudo- 
compounds  in  dynamic  equilibrium,  and  assuming  that  the 
pseudo-compound,  which  so  far  has  not  been  obtained  in  a 
pure  form,  has  a  specific  rotatory  power  +180°  in  benzene 
solution,  then  the  solution,  with  a  rotation  of  —104°,  con- 
tains some  93  per  cent  of  the  normal  and  7  per  cent  of  the 
pseudo  form, 

(B4SO)  2T 


658       XLVII.    PHYSICAL  PROPERTIES  AND  CONSTITUTION 

The  velocity  of  the  transformation,  normal  — *•  pseudo,  is 
increased  by  rise  of -temperature,  by  increase  in  concentration, 
and  by  the  addition  of  traces  of  alkalis. 

Both  the  normal  and  pseudo  forms  of  7r-bromo-nitro-camphor 
have  been  isolated  (Lapworth  and  Kipping,  J.  C.  S.  1896,  304). 
The  compound,  melting  at  142°,  when  dissolved  in  benzene, 
gives  an  initial  specific  rotatory  power  +1S80,  which  changes 
to  —38°  in  a  3'33-per-cent  benzene  solution,  and  appears  to 
be  the  pseudo  form.  The  compound  melting  at  1083  shows 
a  change  in  rotatory  power  from  —51°  to  —38°,  and  appears 
to  be  the  normal  compound.  When  either  of  the  two  pure 
compounds  is  dissolved  in  benzene,  tautomeric  change  occurs, 
and  a  mixture  of  the  two  compounds  in  dynamic  equilibrium 
is  obtained.  From  the  specific  rotatory  power  of  this  solution, 
viz.  —38°,  it  follows  that  it  contains  some  5*5  per  cent  of 
pseudo-compound  for  94*5  of  the  normal. 

XThe  change  in  rotation  of  an  optically  active  solution  is 
usually  known  as  mutarotation  (p.  309),  and  is  a  property 
exhibited  by  various  optically  active  compounds,  especially 
sugars,  e.g.  glucose,  galactose,  xylose,  milk-sugar,  and  maltose, 
and  certain  hydroxy-acids  and  their  lactones,  e.g.  anhydrous 
lactic  acid. 

In  all  cases  the  rotation  changes  when  the  solution  is  kept; 
with  glucose,  for  example,  the  value  decreases  to  half,  with 
milk-sugar  the  values  are  as  1'6:1,  with  galactose  1*46:1,  and 
with  xylose  4'67 : 1.  The  rotatory  powers  of  maltose  and  lactic 
acid  solutions  increase  when  kept. 

All  acids  and  alkalis  appear  to  facilitate  the  conversion,  and 
in  the  order  of  their  degree  of  ionization.  Common  salt,  alco- 
hol, and  various  organic  compounds,  on  the  other  hand,  tend 
to  retard  the  transformation. 

Various  theories  have  been  brought  forward  in  order  to 
account  for  the  phenomenon.  The  first  of  these  assumed  the 
presence  of  complex  molecules,  e.g.  (C6H1206)X,  in  the  freshly- 
prepared  solution,  and  the  gradual  decomposition  of  these  into 
the  simpler  molecules,  C6H1206,  thus  producing  a  lowering  of 
the  rotatory  power.  The  assumption  of  the  presence  of  com- 
plex molecules  was  rendered  untenable  as  soon  as  it  was  shown 
that  the  molecular  weight,  as  determined  by  the  cryoscopic 
method,  is  the  same  in  the  freshly  -  prepared  and  the  old 
solution.  The  second  explanation  was  that,  after  solution, 
water  is  either  withdrawn  from  or  added  on  to  the  original 
molecular  aggregates.  The  latest  theory  is  that  the  different 


MUTAROTATION  659 

rotations  are  due  to  different  isomeric  substances  present  in 
the  two  solutions,  and  that  a  gradual  change  in  rotation 
accompanies  the  conversion  of  the  one  isomeride  into  the 
other. 

Tanret  (1895)  claimed  to  have  isolated  three  distinct  modi- 
fications of  (/-glucose,  which  had  the  respective  specific  rotatory 
powers  a  =  +105°,  j3  =  -f-52'5,  and  7  =  +22-5.  More 
recent  work  (E.  F.  Armstrong,  J.  C.  S.  1903,  1305;  1904,  1043) 
indicates  that  in  the  case  of  (/-glucose  only  two  distinct  iso- 
merides  actually  exist  in  solution,  viz.  the  a  and  7,  and  that 
the  so-called  /^-modification  is  merely  a  mixture  of  the  a  and 
7  in  chemical  equilibrium.  The  a-  and  7-modifications  are 
represented  as  stereo -isomeric,  and  correspond  in  structure 
with  the  a-  and  /3-methyl-glucosides  (p.  310),  since  these  glu- 
cosides,  when  hydrolysed  with  enzymes,  have  rotatory  powers 
of  the  order  of  those  of  the  a-  and  7-glucoses,  and  the  addition 
of  an  alkali  to  the  products  of  hydrolysis  produces  the  same 
change  as  with  the  a-  and  7-sugars.  They  are  therefore  now 
termed  a-  and  /^-glucoses,  and  may  be  represented  by  the 
configurations : 

OH.CH2.CH(OH).CH.CH(OH).CH(OH).C<oH(a) 

and    OH.CH2.CH(OH).CH.CH(OH).CH(OH).C<2H  O8) 

(Compare  also  Behrend  and  Both,  A.  1904,  331,  359,  and 
Lowry,  J.  C.  S.  1904,  1551).  Lowry  concludes  that  in  an 
ordinary  solution  of  glucose,  in  addition  to  the  a-  and  /?- 
modifications,  small  amounts  of  the  aldehyde  or  aldehyde- 
hydrate  are  also  present.  This  accounts  for  the  aldehydic 
properties  of  glucose  solutions,  and  also  affords  an  explanation 
of  the  conversion  of  the  a-  into  the  /3-glucose: 

H-C-OH  CH(OH)2  OH-CH 

'CH-OH  CH-OH  X^CH-OH 

XVH.OH  ^      CH.OH  °XCH.OH 

CH  CH-OH  CH 

CH-OH  CH-OH  CH-OH 

CH2-OH  CH2-OH  CH2-OH 

a-Glucose  Aldehyde-hydrate  p-Glucoae. 

(For  rwimt,  see  Lowry,  B.  A.  Kep.  1904,  193.) 


660      XLVII.   PHYSICAL  PROPERTIES   AND  CONSTITUTION 

Asymmetric  Synthesis. — It  has  already  been  stated  that  the 
product  formed  by  the  synthesis  of  a  compound  containing  an 
asymmetric  carbon  atom  from  symmetrical  compounds  is  al- 
ways a  mixture  or  compound  of  the  d-  and  /-modifications  in 
equal  amounts,  and  a  single  active  modification  can  only  be  ob- 
tained by  the  resolution  of  this  r^cemic  compound  or  mixture. 
Numerous  attempts  have  been  made  to  carry  out  an  asym- 
metric synthesis,  i.e.  according  to  Marckwald  (B.  1904,  37, 1368), 
to  obtain  artificially  an  optically  active  compound  from  a  sym- 
metrical substance  by  the  employment  of  an  active  product 
but  without  the  use  of  an  analytical  process  (such,  for  example, 
as  those  involved  in  the  usual  separation  of  racemic  mixtures). 
A  synthesis  suggested  by  E.  Fischer  was  as  follows: — By  the 
cyanhydrin  reaction  mentioned  on  p.  304  it  is  possible  to  trans- 
form an  optically  active  monose  containing  Cn  into  a  mixture 
of  two  active  sugars  containing  Cn+1.  The  amounts  of  the  two 
active  compounds  vary  considerably  in  different  cases,  and  with 
d-mannose  only  one  c/-mannoheptose  can  be  isolated.  Similarly 
the  d-mannoheptose  yields  only  one  mannooctose,  and  this 
only  one  nonose.  If  it  were  possible  by  some  method  to  de- 
compose this  d-manno-nonose  so  as  to  regenerate  ctanannose 
then  the  other  product  would  be  an  active  glyceric  aldehyde : 

Mannononose,  CHO  •  CH(OH)  •  CH(OH)4-CH(OH)  •  [CH  •  OH]4 •  CH2OH 

-*  glyceric  aldehyde,  CHO.CH(OH).CH2.OH  and 
CHO.LCH.OHJ4.CH2.0H. 

Cohen  and  Whiteley  (J.  C.  S.  1901,  1305),  starting  with  cm 
namic  acid,  prepared  active  amyl  and  menthyl  esters,  to  which 
they  added  bromine  and  then  attempted  to  obtain  an  active 
cinnamic  acid  dibromide,  CgH^  •  CHBr  -  CHBr  •  C02H,  by  the 
hydrolysis  of  the  esters,  but  without  success.  The  hydrolysis 
of  the  products  obtained  by  reducing  the  active  amyl  and 
menthyl  esters  of  mesaconic,  a-methylcinnamic,  and  pyruvic 
acids  gave  rise  to  inactive  acids.  Similar  negative  results  were 
obtained  by  Kipping  (P.  1900,  226).  A.  M'Kenzie  (J.  C.  S. 
1904,  1250;  1905,  1373;  1906,  365)  has  succeeded  in  accom- 
plishing several  asymmetric  syntheses.  Thus  when  /-menthyl  ( 
pyruvate,  CH3  •  CO  •  CO  •  OC10H19,  is  reduced  by  aluminium 
amalgam,  a  mixture  of  unequal  amounts  of  /-menthyl  d-lactate 
and  /-menthyl  /-lactate  is  formed.  When  this  mixture  is  hy- 
drolysed  by  an  excess  of  alcoholic  potassic  hydroxide  and  the 
/-menthol  removed,  a  dextro-rotatory  potassic  salt  containing 


THE  WALDKN  INVERSION  661 

an  excess  of  Mactate  over  d-lactate  is  produced  ;  this  mixture, 
when  acidified,  becomes  laevo-rotatory,  and  the  asymmetric 
synthesis  of  /-lactic  acid  is  thus  accomplished.  If  tmenthyl 
benzoylformate,  C6H5  •  CO  •  C02  •  C10H19,  is  treated  in  exactly 
the  same  manner,  the  final  product  is  r-mandelic  acid,  due, 
probably,  to  the  racemizing  effect  of  the  alkali.  A  second 
asymmetric  synthesis  has  been  accomplished  by  M'Kenzie  by 
means  of  Grignard's  reaction.  Thus  Z-menthyl  benzoylformate 
and  magnesium  methyl  iodide  yield  the  additive  compound 
CMePh(O.MgI)(C02ClpH]9),  which  is  converted  by  dilute 
acids  into  the  Z-menthyl  phenylmethylglycollate  CMePh(OH) 
(C02C]0H19),  from  which,  on  hydrolysis  with  alcoholic  potas- 
sium hydroxide,  a  laevo-rotatory  potassium  phenylmethylgly- 
collate, CMePh(OH)(C02K),  was  obtained.  Thus 


C6H5.CO-C02H  -*  CeH5.CO.COAoH19  —  C6H6.C(CH8)(OH)(C02C1oH19) 
Inactive  Active  Active 

-*  C6H5.C(CH3)(OH)(C02H) 
Active. 

Similar  active  acids  have  been  obtained  by  using  other  Ghignard 
reagents  in  conjunction  with  /-menthyl  benzoylformate. 

For  a  further  asymmetric  synthesis,  see  Marckwald,  B.  1904, 
37,  349. 

The  Walden  Inversion.  —  In  a  chemical  reaction  in  which 
one  radical  is  displaced  by  another,  it  is  usually  assumed  that 
the  group  introduced  takes  the  place  of  the  radical  removed, 
unless  reasons  to  the  contrary  can  be  adduced.  When  an 
optically  active  compound  is  used  we  should  expect  the  pro- 
duct formed  to  correspond  in  configuration  with  the  original 
substance  That  this  is  not  always  true  follows  from  the  fact 
that  during  certain  reactions  racemization  occurs,  and  the  pro- 
duct obtained  is  optically  inactive  (cf.  p.  257).  Even  more 
remarkable  than  this  is  the  phenomenon  known  as  Walden's 
inversion.  An  example  of  this  is  met  with  in  the  conversion 
of  J-chloro-succinic  acid  into  the  d-isomeride  by  the  following 
series  of  reactions  : 

J-Chloro-acid        —  *       £-malic  acid    —  •*•   c?-chloro-acid. 

Moist  Ag20  PC15 

It  is  not  possible  to  say  which  of  the  two  reactions  is  normal 
and  which  abnormal,  as  although  the  malic  acid  may  be  laevo- 
rotatory,  its  configuration  may  correspond  with  that  of  the 
d-chloro-acid  and  not  with  that  of  the  /-acid. 

(B.  32,  1833)  carried  out  a  remarkable  series  of 


662       XLVII.   PHYSICAL  PROPERTIES  AND  CONSTITUtiOtf 


experiments  on  the  reaction  between  /-chloro-  and  /-bromo- 
succinic  acids  and  various  alkalis.  He  found  that  the  hydrox- 
ides of  potassium,  rubidium,  and  ammonium  gave  practically 
pure  c/-malic  acid,  moist  silver  oxide  gave  the  pure  /-malic 
acid;  and  the  hydroxides  of  sodium,  barium,  lead,  and  lithium 
gave  mixtures  in  which  the  d-acid  preponderated,  whereas 
oxides  of  mercury  and  palladium  gave  mixtures  in  which  the 
/-acid  was  in  excess.  The  conclusion  was  drawn  that  the 
reaction  with  potassium  hydroxide  is  normal,  and  that  inver- 
sion occurs  when  silver  oxide  is  used. 

Interesting  cases  are  those  in  which  a  complete  cycle  is 
involved,  e.g.: 

1.  /-Chloro-succinic  acid  — *•        /-malic  acid 

I  ifototAoO  , 

7  I        *  Moist  Ag20  * 

a-mahc  acid  •* —        a-chloro-succmic  acid. 

2.  d- Alanine  — *•        /-bromo-propionic  acid 

t  NH  NOBr  I  NH 

c?-bromo-propiomc  acid          «*—        /-alanine. 

3.  d-C6H5.CH(OH).C02H          *-       /-C6H6.CH(NH2).C02H 

I  T>™  HN°2  t  xrrr 


/-C6K6.CHC1.C02H 


d-C6H5.CHCl-CO2H 


.  CH(NH2)  •  C02H 


In  some  of  these  cases  it  is  possible  to  determine  in  which 
of  the  different  reactions  inversion  occurs;  thus  in  Example 
No.  2  the  reaction  with  nitrosyl  bromide  is  abnormal  and  not 
that  with  ammonia,  as  E.  Fischer  has  shown  that  under  very 
varying  conditions  ammonia  always  gives  the  same  product. 
With  NOBr  c?-alanine  gives  /-bromo  acid,  but  the  ester  of 
r/-alanine  reacts  with  NOBr,  giving  d-bromo-propionic  acid. 
/-Valin  (amino-isovaleric  acid),  with  NOBr  gives  the  /-bromo 
acid,  and  this  with  ammonia  yields  /-valin. 

Practically  all  the  inversions  mentioned  above  occur  wiien 
the  asymmetric  carbon  atom  has  a  carboxyl  group  attached 
to  it.  Experiments  made  by  E.  Fischer  and  Scheibler,  with 
compounds  in  which  the  asymmetric  atom  is  in  the  /3-position 
with  respect  to  the  carboxylic  group,  prove  that  inversion 
does  not  take  place: 

PC1-, 

«-CHa.CH(OH).CH2.C02H    =r    d-CH3.CH(OH).CH2.C02II, 
AftO 


WALDEN   INVERSION  663 

and  similar  results  are  obtained  when  the  methyl  esters  are 
used.  The  same  holds  good  in  the  case  of  /3-hydroxy-/?-phenyl- 
propionic  acid  (M'Kenzie  and  Humphreys).  There  are,  how- 
ever, several  exceptions,  e.g.  : 

1.  Fischer: 

c?-/3-Amino-butyric  acid    —  *•    Z-/3-hydroxy-butyric  acid 
NOCI 


£-j8-chloro-butyric  acid      —  «•   c?-/3-hydroxy-butyric  acid. 
Water 

2.  M'Kemie  and  Barrow: 

c?-/3-Hydroxy-)S-phenyl-propionic  acid 

—  *•    c?-j8-chloro-/3-phenyl-propionic  acid 
80C1*  J  Water 

J-j3-hydroxy-j8-phenyl-propionic  acid. 

Frequently  phosphorus  pentachloride  and  thionyl  chloride 
react  differently,  e.g.: 

PC15 

£-Mandelic  acid  or  ester    —  *    c?-chloro  acid  or  ester 
Z-mandelic  acid  or  ester     —  *•    Z-chloro  acid  or  ester. 

SOC12 

In  connection  with  this  the  following  cycles  are  of  interest. 

Z-Mandelic  acid          —  *•    d-chloro  acid 

f  NaOH  rcl«  J  NaOH 

Z-chloro  acid  *—    c?-mandelic  acid 

PC16 

MVIandelic  acid          —  ••    ^-chloro  acid 

J  Ag2C03  +  water  SOCI2  J  Ag2C03  +  water 

c?-chloro  acid  *—    c?-mandelic  acid. 

SOC12 


of  ^8-hydroxy-^-phenyl-propionic  acid  it  has  been 
the  reaction  with  thionyl  chloride  is  normal,  since 


In  the  case 
shown  that  the 

the  chloro  ester  derived  from  the  Z-hydroxy  ester  is  trans- 
formed back  into  Z-hydroxy  acid  when  warmed  with  water  and 
marble. 

(For  details  see  Walden,  B.  28,  2772;  29,  133;  30,  3146 
E.  Fischer  and  students,  B.  41,  889,  2891;  42,  1219;  43, 
2020;  A.  381,  123;  383,  337;  386,  374.  Werner,  A.  386,  65. 
MlKenzie  and  others,  J.  C.  S.  1908,  811;  1909,  777;  1910, 
121,  1016,  1355,  2564;  1911,  1910,  1912,  390.  Bulmann,  A. 
1912,  388,  330.) 


664      XLVII.   PHYSICAL  PROPERTIES  AND  CONSTITUTION 

I.  Electrical  Conductivity. — Attention  has  previously  (p, 
161)  been  drawn  to  the  fact  that  the  degree  of  ionization,  a, 
of  an  acid  in  solutions  of  given  concentration,  v,  may  be  deter- 
mined by  a  comparison  of  the  electrical  conductivity,  X  (re- 
ciprocal of  resistance),  at  that  dilution  with  the  conductivity 
at  infinite  dilution  when  ionization  would  be  complete,  i.e. 

a  =  — .     From  Ostwald's  dilution  law,  based  on  the  law  of 
aoc  2 

mass  action,  it  follows  that  — -  is  a  constant  =  &,  where 

v(l  -  a) 

v  =  number  of  litres  of  solution  containing  one  equivalent  of 
acid.  This  constant  k  (or  100&  =  K)  is  known  as  the  dis- 
sociation constant,  and  is  used  as  a  measure  of  the  strength  of 
all  feeble  acids.  The  effect  of  the  introduction  of  strongly 
negative  groups  into  the  acid  molecule  on  this  constant  has 
been  referred  to  (pp.  168,  447),  and  the  influence  of  strongly 
positive  groups,  e.g.  NH2,  is  equally  marked.  Thus  benzoic 
acid  ==  0*006,  0-amino-benzoic  =  0*0009,  m-amino-benzoic  = 
O'OOIO,  and  jp-amino-benzoic  =  O'OOS. 

Hantzsch  has  used  the  electrical  conductivity  method  in  the 
diagnosis  of  pseudo-acids  and  bases.  Thus  with  certain  nitro- 
compounds  the  ordinary  compound  R-CH2»N02  is  a  pseudo- 
acid  and  the  isonitro-compound  R«CH:NO«OH  is  a  true  acid, 
and  all  the  salts  are  derived  from  the  latter.  These  salts,  as  a 
rule,  are  but  little  hydrolysed,  as  the  isonitro-compounds  are 
relatively  strong  acids.  A  solution  of  such  a  salt  will  thus 

contain  the  metallic  ions  and  the  isonitro-ion  K»CH:NO»0«. 
When  this  solution  is  mixed  with  an  equivalent  quantity  of 

hydrochloric  acid  the  ions  present  are  Na,  Cl,  E-CH:NO«0', 

+ 

and  H.  In  the  majority  of  cases  there  is  a  considerable  ten- 
dency for  the  strongly  acidic  and  hence  strongly  ionized 
isonitro-compound  (true  acid)  to  become  transformed  into  the 
ordinary  nitro-compound  (pseudo-acid).  As  this  is  practically 
a  non-electrolyte,  it  follows  that  as  this  transformation  occurs 
the  conductivity  of  the  solution  will  gradually  diminish  until 
it  attains  the  value  of  a  sodium  chloride  solution  of  the  given 
concentration.  Thus  with  sodium  ^-bromophenylnitromethane, 
C6H4Br.CH:NO.ONa,  at  25°,  and  0=  256,  after  mixing  with 
an  equivalent  of  hydrochloric  acid,  the  conductivity,  /*  =  151 '4 
after  1-5  minute,  and  after  45  minutes  a  constant  value  p  =  129-5 
was  obtained.  This  approximates  to  the  value  /^  =  114'4 


ELECTRICAL  CONDUCTIVITY  665 

for  sodic  chloride,  and  the  difference  may  be  due  to  secondary 
changes. 

Similar  results  have  been  obtained  with  pseudo-bases.  The 
true  base,  methyl-phenyl-acridonium  hydroxide  (I),  which  is 
first  liberated  when  salts  of  the  base  are  decomposed  with 
alkali,  is  readily  transformed  into  the  pseudo-base  with  the 
carbinol  formula  (II): 


—  II 


which  is  practically  a  non-electrolyte.  When  a  solution  of  the 
chloride  of  the  base  is  neutralized  with  an  equivalent  of  sodic 
hydroxide,  the  solution  has  a  maximum  conductivity  which 
gradually  diminishes  until  the  value  for  a  solution  of  sodic 
chloride  of  the  given  concentration  is  practically  reached. 
Similarly  with  the  sulphate  and  an  equivalent  quantity  of 
barium  hydroxide;  at  0°  and  v  =  256,  the  initial  conductivity 
was  /*=  119'2,  but  after  15  hours  it  had  fallen  to  ft  =  1-7  (due 
to  small  amounts  of  dissolved  baric  sulphate).  Phenomena 
of  this  kind,  which  are  termed  by  Hantzsch  "slow  neutrali- 
zation ",  are  largely  used  to  denote  tautomeric  change,  i.e.  the 
change  from  a  true  acid  to  a  pseudo-acid  or  from  a  true  base 
to  a  pseudo-base  (cf.  p.  485)  during  the  conversion  of  the  salt 
into  the  acid  or  base. 

The  study  of  other  physical  properties  such  as  Internal 
Viscosity  (Zeit.  phys.  1887,  1,  285,  293;  1888,  2,  744;  com- 
pare also  Dunstan,  J.  C.  S.  1907,  1728;  1908,  1815,  1919; 
1909,  1556;  1910,  1935),  Heat  of  Combustion  (Stohmann, 
Zeit.  phys.  1890,  6,  334;  1892,  10,  410),  Capillary  Constants 
(Schiff,  A.  1884,  223,  47),  Magnetic  Susceptibility  (Pascal, 
Bull.  1909,  1110;  1910,  17,  45;  1911,  6,  79,  134,  177,  336, 
809.  868)  indicate  that  here  also  there  are  similar  relation- 
ships between  constitution  and  physical  properties. 


666  XLVIIL    FERMENTATION   AND   ENZYME   ACTiOJi 


XLVIII.  FERMENTATION  AND  ENZYME  ACTION 

A.  Alcoholic  Fermentation. — Lavoisier,  1789,  was  the  first 
to  recognize  that  alcoholic  fermentation  consists  essentially 
in  the  ^decomposition  of  a  sugar  into  alcohol  and  carbon 
dioxide;  and  Gay-Lussac,  1810,  drew  attention  to  the  fact  that 
the  presence  of  air  appeared  to  be  essential  for  fermentation 
and  putrefaction  to  take  place.  The  fact  that  brewers'  yeast 
is  a  low  form  of  plant  life  was  discovered  independently  by 
Cagnaird-Latour,  Theodor  Schwann,  and  Kutzing,  1837.  By 
microscopical  examination  they  observed  the  growth  of  the 
organism,  and  showed  that  it  could  be  destroyed  by  heat  or 
by  certain  poisons.  These  results  were  not  accepted  by 
Berzelius,  Liebig,  and  others,  who  still  regarded  yeast  as  a 
chemical  substance  without  life.  According  to  Berzelius  the 
yeast  acted  as  a  contact  substance  which  decomposes  the 
sugar  without  undergoing  change  itself;  whereas  Liebig  re- 
garded the  ferment  as  an  extremely  susceptible  substance, 
which  undergoes  a  change  of  the  nature  of  decay,  and  sug- 
gested that  the  decomposition  of  the  sugar  was  a  type  of 
sympathetic  reaction  induced  by  the  change  of  the  ferment. 
In  1857  Pasteur  began  his  researches  on  fermentations.  He 
was  able  to  show  that  in  other  cases  of  fermentation,  such  as 
the  lactic  fermentation  of  milk,  micro-organisms  are  present. 
He  was  further  able  to  show  that  during  alcoholic  fermenta- 
tion the  yeast  grows  and  multiplies,  and  was  led  to  the 
conclusion  that  fermentation  is  a  physiological  process  ac- 
companying the  life  of  the  yeast. 

In  his  own  words:  "I  am  of  opinion  that  alcoholic  fer- 
mentation never  occurs  without  simultaneous  organization, 
development,  multiplication  of  cells,  or  the  continued  life  of 
cells  already  formed".  This  conclusion  harmonized  with  the 
facts  already  known  that  boiled  liquids  could  be  kept  from 
fermenting  by  heating  or  filtering  through  cotton  wool  the 
air  admitted  to  the  liquid. 

It  was  Pasteur  who  proved  that  only  95  per  cent  of  the  glu- 
cose is  accounted  for  as  carbon  dioxide  arid  alcohol ;  he  was  able 
to  isolate  glycerol  and  succinic  acid  from  the  final  products. 

As  early  as  1858  M.  Traube  expressed  the  view  that  all 
fermentations  produced  by  living  organisms  are  ultimately 
due  to  ferments,  which  are  definite  chemical  substances  manu- 
factured in  the  cells  of  the  organism.  These  ferments  he  re- 


ALCOHOLIC  FERMENTATION  667 

garded  as  analogous  to  proteins.  Traube's  conclusions  have 
been  verified  in  the  case  of  alcoholic  fermentation  by  Buchner's 
isolation  of  "  zymase  "  from  yeast  (see  p.  77).  Buchner's  yeast 
juice,  when  quite  free  from  yeast  cells,  can  ferment  solutions 
of  glucose,  fructose,  sucrose,  and  maltose;  and  the  fermenting 
power  is  not  destroyed  by  the  addition  of  chloroform,  benzene, 
or  sodium  arsenite,  antiseptics  which  inhibit  the  action  of 
living  cells,  by  filtration  through  a  Berkefeld  filter,  by  eva- 
poration to  dryness  at  30°-35°,  or  by  precipitation  with 
alcohol.  The  fermenting  power  is,  however,  completely  de- 
stroyed by  heating  to  50°,  or  by  the  addition  of  powerful  anti- 
septics. The  activity  of  the  juice  diminishes  in  the  course  of 
time,  as  a  digestive  enzyme  is  also  present  which  gradually 
decomposes  the  zymase.  Both  in  rate  of  fermentation  and  in 
the  total  fermentation  produced,  the  extract  or  juice  is  much 
less  efficient  than  the  equivalent  amount  of  living  yeast,  and 

g'ycerol  is  formed  as  a  by-product  when  the  extract  is  used, 
uring  fermentation  a  portion  of  the  sugar  is  converted  into 
a  compound  of  less  reducing  power  which  is  not  fermented, 
but  which  yields  sugar  when  hydrolysed  with  acids.  Per- 
manent preparations  containing  zymase  can  be  obtained  by 
evaporating  the  juice  to  a  syrup  at  20°-25°,  drying  at  35°,  and 
then  exposing  to  sulphuric  acid  in  a  vacuum  desiccator.  Such 
a  powder  when  dry  retains  its  activity  for  twelve  months,  and 
can  be  heated  at  85°  for  eight  hours  without  any  serious  loss 
of  fermenting  power.  Another  preparation  can  be  obtained 
by  bringing  the  juice  into  10  volumes  of  acetone,  centrifuging, 
washing  the  precipitate  with  acetone  and  then  with  ether, 
and  drying  over  sulphuric  acid.  An  important  medicinal 
preparation  known  as  zymin  is  manufactured  by  stirring 
moist  yeast  with  acetone,  filtering  and  draining  at  the  pump, 
again  mixing  with  acetone  and  draining.  The  product  is 
then  roughly  powdered,  kneaded  with  ether,  filtered,  drained, 
and  spread  on  filter  paper  or  porous  plates,  and  finally  dried 
at  45°  for  twenty-four  hours.  This  product  is  quite  incapable 
of  growth  or  reproduction,  but  produces  fermentation  and 
is  much  more  active  than  yeast  extract. 

The  researches  of  Harden  and  Young  (Abs.  1905,  ii.  109; 
1906,  i.  470)  indicate  that  the  activity  of  yeast  juice  or  ex- 
tract is  due  to  an  enzyme  and  a  co-enzyme,  which  can  be 
separated  by  filtration  or  dialysis  through  a  Martin  gelatin 
filter;  the  residue  contains  the  enzyme,  and  the  filtrate  or 
dialysate  the  co-enzyme.  Neither  by  itself  can  induce  fer- 


668  XLVIII.    FERMENTATION   AND  ENZYME  ACTION 

mentation,  but  a  mixture  of  the  two  is  equal  in  activity  to 
the  original  juice.  The  co-enzyme  is  dialysable,  and  is  not 
destroyed  by  boiling,  but  disappears  from  yeast  juice  during 
fermentation,  or  when  the  juice  is  allowed  to  undergo  auto- 
lysis.  It  cannot  be  a  protein,  and  its  nature  has  not  yet  been 
determined.  It  is  decomposed  by  acid  or  alkaline  hydrolysing 
agents,  by  repeatedly  boiling  the  extract,  and  also  by  the 
lipase  of  castor-oil  seeds.  In  the  case  of  other  fermentations 
brought  about  by  enzymes,  e.g.  lipase,  it  has  been  clearly 
demonstrated  that  both  enzyme  and  co-enzyme  are  necessary, 
and  also  that  the  co-enzyme  is  a  metallic  salt  of  the  com- 
plex taurochloric  acid  (p.  196).  Harden  and  Young  (Abs. 
1908,  i.  590)  have  also  shown  that  phosphates  added  to  a 
mixture  of  glucose  and  yeast  juice  produce  both  an  initial 
acceleration  and  also  an  increased  total  fermentation.  An 
optimum  concentration  of  phosphate  exists  which  produces  a 
maximum  initial  rate  of  fermentation;  an  increase  beyond  this 
optimum  diminishes  the  rate.  The  reaction  between  the  glu- 
cose and  phosphate  is  represented  by  the  following  equations  :  — 
2C6H1206  +  2Na2HP04 

=  2C02  +  2C2H60  +  C6H1004(P04Na2)2  +  2H20 
and      C6H10O4(P04Na2)2-f  2H2O  =  C6H12O6 


According  to  the  second  of  these,  the  glucose  phosphate  is 
hydrolysed  by  the  water  and  yields  sodium  phosphate,  which 
can  then  react  with  a  further  quantity  of  glucose.  These 
conclusions  are  supported  by  the  following  facts.  Careful 
experiments  have  shown  that  during  the  period  of  increased 
fermentation  the  amounts  of  alcohol  and  carbon  dioxide  pro- 
duced exceed  those  which  would  have  been  formed  in  the 
absence  of  added  phosphate  by  a  quantity  exactly  equivalent 
to  the  phosphate  added  in  the  ratio  C2H60  :  Na2HP04.  (Com- 
pare also  Iwanoff,  Abs.  1909,  1,  752.)  It  has  been  proved  that 
the  metallic  phosphate  is  not  the  co-enzyme  already  mentioned, 
as  the  filtered  enzyme  and  phosphate  are  not  capable  of  induc- 
ing fermentation  in  the  absence  of  the  filtrate.  Fermentation 
does  not  proceed  in  the  absence  of  phosphate  although  both 
enzyme  and  co-enzyme  are  present,  and  although  arsenates 
and  arsenites  have  accelerating  actions  on  the  rate  of  fer- 
mentation they  cannot  be  used  in  place  of  the  phosphate. 
The  function  of  the  arsenate  or  arsenite  appears  to  be  to  act 
as  accelerators  in  the  decomposition  of  the  glucose  phosphate. 
Slator  finds  that  phosphates  have  not  an  accelerating  effect 


ALCOHOLIC  FERMENTATION  669 

when  living  yeast  cells  are  employed.  He  has  estimated 
(J.  C.  S.  1906,  89,  128;  1908,  93,  217)  the  amounts  of  car- 
bon dioxide  evolved  during  given  periods  of  time  when  yeast 
itself  is  used,  and  finds  that  the  rate  of  fermentation  is  exactly 
proportional  to  the  amounts  of  yeast  present,  and  is  almost 
independent  of  the  concentration  of  the  glucose.  A  yeast 
which  can  ferment  glucose  does  not  necessarily  ferment  iso- 
meric  sugar,  e.g.  galactose;  it  is  probable  that  different 
enzymes  are  required  for  the  different  sugars. 

The  fermentation  of  glucose  undoubtedly  consists  of  a  whole 
series  of  chemical  reactions;  at  present  we  know  the  sub- 
stances we  start  with  and  the  final  products  obtained.  Several 
suggestions  have  been  made  with  regard  to  the  nature  of  some 
of  the  intermediate  products.  Buchner  and  Meisenheimer  (B. 
1905,  38,  620)  have  suggested  that  lactic  acid  (p.  213)  is  first 
formed  by  the  action  of  zymase  on  glucose,  and  that  a  second 
enzyme,  lactacidase,  then  decomposes  the  lactic  acid  into  ethyl 
alcohol  and  carbon  dioxide.  A  serious  objection  to  this  view 
is  that  lactic  acid  itself  is  only  very  slowly  fermented  by 
yeast  (Slator). 

Another  suggestion  is  that  dihydroxy-acetone,  CO(CH2«  OH)2, 
is  an  intermediate  product,  and  it  has  been  proved  that  this 
compound  can  be  fermented  by  yeast  (Buchner  and  Meisen- 
heimer, B.  43,  1773;  Lebedew,  44,  2932);  compare  also  Fmnzen 
and  Steppuhn,  ibid.,  2915. 

Of  the  by-products  mentioned  on  p.  76,  glycerol  is  formed 
from  the  sugar,  as  Buchner  and  Meisenheimer  have  shown  that 
it  is  also  formed  when  yeast  extract  or  zymin  acts  on  sugar 
solutions.  The  fusel  oil  and  succinic  acid,  on  the  other  hand, 
do  not  owe  their  origin  to  the  sugar,  but  to  other  products 
present  in  the  mixture  undergoing  alcoholic  fermentation. 
The  researches  of  F.  Ehrlich  (1904-1910)  prove  that  the 
alcohols  and  also  the  aldehydes  present  in  ordinary  fusel  oil 
are  derived  from  the  amino-acids  formed  by  the  hydrolysis 
of  proteins.  Thus  isoamyl  alcohol,  one  of  the  chief  consti- 
tuents of  fusel  oil,  is  closely  related  to  leucine,  a-amino 
isohexoic  acid,  and  active  amyl  alcohol  to  isoleucine,  a-amino- 
/J-methyl-valeric  acid,  both  of  which  are  formed  by  the  hy- 
drolysis of  proteins,  and  according  to  Ehrlich  both  these  acids 
are  transformed  into  the  corresponding  amyl  alcohols  under 
the  influence  of  pure  yeast  cultures,  in  the  presence  of  sugar: 

HO 


670  XLVIII.    FERMENTATION   AND   ENZYME  ACTION 

These  changes,  although  brought  about  by  yeast,  do  not 
occur  when  zymin  or  yeast  extract  is  used.  Other  amino 
acids  undergo  a  similar  decomposition  :  tyrosine  (p.  459)  yields 
2?-hydroxy-phenyl-ethyl-alcohol,  tyrosol,  OH  •  C6H4  •  CH2  •  CH2  • 
OH,  and  phenyl-alanine  (p.  453)  gives  phenyl-ethyl  alcohol. 

The  ammonia  is  not  found  at  the  end  of  the  reaction,  as  it 
is  used  up  by  the  organism  for  the  purpose  of  building  up 
new  protein  molecules.  If  appreciable  amounts  of  simple 
nitrogenous  substances,  such  as  ammonium  salts,  are  originally 
present  in  the  fermenting  liquor,  the  organism  uses  these  in 
preference  to  decomposing  the  amino-acids;  and  Ehrlich  has 
found  it  possible  to  increase  or  diminish  the  amounts  of  fusel 
oil  formed,  by  diminishing  or  increasing  the  amounts  of  am- 
monium salts  present  at  the  beginning  of  the  fermentation. 
Practically  all  amino-acids  formed  by  the  hydrolysis  of  pro- 
teins can  undergo  similar  decomposition  by  yeast,  but  only 
in  the  presence  of  sugar.  The  succinic  acid  found  as  a  by- 
product in  alcoholic  fermentation  is  probably  formed  in  a 
similar  manner  from  glutamic  acid. 

According  to  Neuberg  and  Fromherz  (1911),  ketonic  acids 
are  probably  formed  as  intermediate  products  in  the  fermen- 
tation of  amino-acids  to  alcohols;  and  Neuberg  has  been  able  to 
show  that  many  a-ketonic  acids,  e.g.  pyruvic,  CH3-CO«C02H, 
and  oxalacetic,  C02H  •  CH2  •  CO  •  C02H,  are  readily  decom- 
posed by  yeast  even  in  the  absence  of  sugar,  yielding  carbon 
dioxide  and  aldehyde  : 

CH3.CO.C02H  —  C 


With  a  1-per-cent  solution  of  pyruvic  acid  the  decomposition 
is  almost  as  rapid  as  with  a  sugar  solution.  The  decomposi- 
tion is  probably  due  to  an  enzyme,  termed  "  carboxylase  "  by 
Neuberg. 

For  fermentations  induced  by  organisms  other  than  yeasts, 
see  pp.  150,  152,  214.  According  to  Harden  (J.  C.  S.  1901, 
610),  Badllus  coli  communis  ferments  glucose,  fructose,  or 
mannitol,  yielding  lactic,  succinic,  and  acetic  acids,  alcohol, 
formic  acid,  carbon  dioxide,  and  hydrogen.  The  main  re- 
action can  be  represented  by  the  equation: 

2C6H1206  +  H20  =  2C3Hs03  +  C2H4O2  +  C2H60  +  2C02  +  2H2. 


With  glucose  the  weight  of  lactic  acid  is  practically  50  per 
cent  of  the  sugar,  and  the  alcohol  and  acetic  acid  are  formed 
in  equal  amounts.  The  alcohol  probably  comes  from  the 


ENZYME  ACTION  671 

group  CH2(OH)  •  CH(OH),  and  as  this  group  occurs  twice  in 
the  molecule  of  mannitol  the  yield  of  alcohol  is  much  greater 
when  this  compound  is  used.  The  lactic  acid  is  probably 
derived  from  the  CH  (OH) .  CH  (OH) .  CH(OH)  grouping. 
B.  typhosus  yields  similar  products,  except  that  it  gives  formic 
acid  instead  of  carbon  dioxide  and  hydrogen  (Abs.  1906,  II, 
380). 

B.  Enzyme  Action. — Attention  has  been  drawn  several 
times  (pp.  76,  77,  423)  to  the  fact  that  chemical  decomposi- 
tions can  be  brought  about  by  certain  complex  organic  sub- 
stances found  in  animal  and  plant  tissues.  Such  substances 
are  termed  unorganized  ferments  or  enzymes.  The  great  ma- 
jority act  as  catalysts  in  processes  of  hydrolyses,  e.g.  invertase 
which  hydrolyses  cane  sugar,  amylase  which  hydrolyses  starch, 
emulsin  (p.  423),  myrosin  (p.  593),  pepsin  and  trypsin  (p.  598), 
lipases  which  hydrolyse  esters;  but  in  addition  there  are 
enzymes  which  bring  about  oxidation,  viz.  the  oxidases, 
enzymes  which  bring  about  complex  reactions,  e.g.  zymases. 
The  enzymes  are  unstable  nitrogenous  compounds  of  colloidal 
nature,  but  not  necessarily  proteins.  They  act  as  catalysts, 
in  the  majority  of  cases  as  positive,  but  in  a  few  as  negative. 
The  catalytic  nature  is  shown  by  the  fact  that  the  rate  of 
reaction  is  directly  proportional  to  the  concentration  of  the 
enzyme,  but  that  the  total  decomposition  is  independent  of 
the  amount  of  enzyme,  provided  sufficient  time  is  allowed,  and 
provided  the  enzyme  does  not  undergo  decomposition.  They 
are  sensitive  to  high  temperatures,  e.g.  when  heated  to  below 
100°  their  activity  is  completely  destroyed;  they  are,  how- 
ever, resistant  towards  certain  antiseptics  which  destroy  pro- 
toplasm and  kill  fermenting  organisms.  Strong  antiseptics, 
such  as  formaldehyde,  tend  to  destroy  enzymes.  Enzymes 
are  often  precipitated  from  their  colloidal  solutions  by  the 
addition  of  alcohol  or  acetone,  but  such  products  are  not  pure; 
in  many  cases  they  consist  of  a  mixture  of  enzymes,  and  in 
this  way  the  study  of  their  reactions  is  complicated.  The 
modern  system  of  nomenclature  is  to  name  the  enzymes  ac- 
cording to  the  compounds  they  hydrolyse,  e.g.  maltase,  sucrase 
(  =  invertase),  amylase  (  =  diastase),  &c.^  The  nature  of 
the  products  formed  varies  not  merely  with  the  substance 
used,  but  also  with  the  enzyme;  thus  the  trisaccharose,  raffi- 
nose,  if  hydrolysed  by  acids,  yields  galactose,  fructose,  and 
glucose;  the  same  carbohydrate  with  diastase  yields  melibiose 
and  fructose,  and  with  emulsin  galactose  and  sucrose.  The 


672  XLVIIL   FERMENTATION   AND  ENZYME  ACTION 

action  of  enzymes  is  essentially  selective,  and  in  this  respect 
differs  from  the  hydrolysing  action  of  alkalis  or  acids.  Thus 
esters,  amides,  carbohydrates,  glucosides,  &c.,  are  all  hydro- 
lysed  by  hydrochloric  acid;  whereas  esters,  but  not  carbo- 
hydrates, can  be  hydrolysed  by  lipases,  and  maltose,  but  not 
sucrose,  can  be  hydrolysed  by  maltase.  Even  a  slight  differ- 
ence in  the  configuration  of  two  isomeric  substances  is  suf- 
ficient to  affect  their  reactivity  with  a  particular  enzyme,  e.g. 
the  two  methyl-glucosides  (p.  659),  which  are  represented  by 
the  spatial  formulae: 


C-OCHg 

H.C-OH\ 


HO.C.H  HO.C.H 


H-C-OH  H-C-OH 

CH2-OH  CH2-OH, 

the  only  difference  being  the  arrangement  of  the  H  and  OCH3 
attached  to  the  upper  carbon  atom.  Of  these  two  compounds 
the  a  can  be  hydrolysed  by  maltase  but  not  by  emulsin,  and 
the  ft  by  emulsin  but  not  by  maltase,  and  hence  the  names 
a  and  p  glucase  are  sometimes  used  for  the  two  enzymes 
maltase  and  emulsin.  Numerous  other  examples  of  the  same 
type  have  been  met  with,  especially  in  the  case  of  polypeptides 
(Fischer  and  Bergell,  B.  36,  2592;  37,  3103).  As  most  of  the 
natural  glucosides  are  hydrolysed  by  emulsin  but  not  by  mal- 
tase, they  are  regarded  as  analogous  to  the  /3-methyl-glucoside, 
with  complex  radicals  in  place  of  the  methyl  group.  Maltose 
on  the  other  hand  is  an  a-glucoside  resembling  the  a-methyl 
compound  in  configuration. 

It  has  been  proved  in  many  cases  that  a  particular  enzyme 
can  act  not  merely  as  a  hydrolysing  but  also  as  a  synthesizing 
agent.  The  process  of  hydrolysis  is  frequently  a  balanced 
reaction,  although  in  the  majority  of  cases  the  equilibrium  is 
mainly  in  the  direction  of  analysis  and  not  synthesis.  The 
synthesizing  activity  of  an  enzyme  was  first  demonstrated  by 
Croft-Hill  (J.  C.  S.  1898,  634;  1903,  578)  in  the  case  of  maltase. 
The  greater  portion  of  the  maltose  is  hydrolysed  to  glucose, 
but  a  certain  proportion  of  disaccharose  is  always  present,  and 


ENZYME  ACTION  673 

in  a  solution  of  glucose  maltase  can  produce  a  certain  amount 
of  a  disaccharose,  which  at  first  was  thought  to  be  maltose, 
but  has  since  been  proved  (E.  F.  Armstrong,  1905)  to  be  a 
mixture  of  maltose  and  isomaltose.  Invertase,  lactase,  emulsin, 
and  lipases  have  all  been  shown  to  possess  synthetical  activity. 
The  formation  of  starch  in  plant  and  glycogen  in  animal 
tissues  is  probably  largely  due  to  the  activities  of  synthesizing 
enzymes;  and  Potterin  has  succeeded  in  synthesizing  atriolein, 
one  of  the  common  constituents  of  natural  fats,  by  means  of  a 
lipase. 

The  rate  of  hydrolysis  by  means  of  enzymes  has  been 
studied  by  different  authorities.  The  investigations  of  O'Sul- 
livan  and  Thompson  (J.  C.  S.  1890,  834)  and  of  Hudson  (J.  Am. 
C.  S.  1908,  1160,  1564;  1909,  655)  prove  that  the  inversion 
of  sucrose  by  invertase  constant  values  for  K  can  be  obtained 
by  using  the  ordinary  equation  for  a  unimolecular  reaction, 
provided  that  the  complications  attending  the  mutarotation 
of  the  glucose  and  fructose  (p.  658)  are  avoided  by  adding  a 
small  quantity  of  alkali  before  taking  the  polarimetric  reading. 
The  alkali  stops  the  inversion,  and  at  the  same  time  rapidly 
brings  about  equilibrium  between  the  a-  and  /3-glucoses  and 
the  a-  and  /3-fructoses,  so  that  the  normal  rotatory  power  of 
invert  sugar  is  given.  Hudson's  results  clearly  prove  that  the 
a-modifications  of  glucose  and  fructose  are  first  formed. 

A  view  generally  held  with  regard  to  the  mechanism  of 
enzyme  reaction  is  that  combination  (absorption  compounds) 
occurs  between  the  enzyme  and  the  substrate  (the  substance 
decomposed),  and  that  it  is  this  compound  which  reacts  with 
water.  The  fact  that  a  specific  enzyme  can  hydrolyse  only 
particular  substrates  is  in  harmony  with  this  view,  as  it  is 
known  that  chemical  constitution  plays  an  important  part  in 
absorption.  In  living  tissues  a  number  of  complex  substances 
are  present  which  are  capable  of  interfering  with  the  action 
of  an  enzyme.  These  are  termed  anti-enzymes.  Some  are 
normally  present  in  tissue,  others  appear  to  be  formed  when 
an  enzyme  is  injected  into  the  tissue. 


674  XLIX.   CATALYTIC  ACTION 


XLIX.    CATALYTIC    ACTION    OF    FINELY -DIVIDED 
METALS  AND   METALLIC  OXIDES 

Attention  has  already  been  drawn  to  the  reduction  of 
carbon  compounds  by  hydrogen  gas,  using  finely -divided 
metals  or  metallic  oxides  as  catalysts  (p.  610).  Within  recent 
years  it  has  been  shown  that  finely-divided  solids  can  act  as 
catalysts  in  various  other  reactions. 

Oxidations. — One  of  the  most  interesting  of  these  is  the 
decomposition  of  primary  alcohols  into  aldehydes  and  hydrogen 
when  passed  through  a  tube  containing  iron,  zinc,  brass,  zinc 
oxide,  ferric  oxide,  or  stannic  oxide.  At  660°  in  the  presence 
of  zinc,  ethyl  alcohol  gives  an  80-per-cent  yield  of  acetalde- 
hyde,  other  primary  alcohols  behave  in  a  similar  manner,  and 
isopropyl  alcohol  gives  an  almost  quantitative  yield  of  acetone. 

The  reactions 

Primary  alcohol      i±   aldehyde  +  Ha 
Secondary  alcohol  ^i±   ketone  -{-  H2 

are  reversible  in  the  presence  of  the  catalyst,  as  an  aldehyde 
and  hydrogen  when  heated  in  contact  with  zinc  or  iron  yield 
an  alcohol.  When  alcohols  are  heated  with  hydrogen  under 
pressure,  and  in  contact  with  zinc  or  iron,  the  final  products 
consist  mainly  of  hydrocarbons  if  the  temperature  is  fairly 
high,  e.g.  isoamyl  alcohol  yields  considerable  amounts  of  pro- 
pane and  methane.  The  formation  of  these  latter  is  probably 
due  to  the  following  series  of  reactions : — 

(CH3)2CH.CH2.CH2.OH  —  (CH3)2CH.CH2.CHO  +  HJJ. 
(CH3)2CH.CH2.CHO         -*  (CH^CH-CHg-f  CO. 
(CH3)2CH.CH3  +  H2         —>  CH3.CH2.CH3-f  CH4. 

Reduced  benzene  derivatives  can  be  oxidized  to  benzene 
compounds,  but  pentamethylene  derivatives  are  not  oxidized. 
Zelinsky  shows  (B.  44,  3121)  that  palladium  black  can  also 
bring  about  oxidations  at  about  200°-300° — e.g.  hexamethy- 
lene  — »  benzene  (ibid.  p.  2302) — and  gives  an  example,  viz. : 
methyl-tetrahydro-terephthalate,  which  is  both  oxidized  and 
reduced  by  hydrogen  in  the  presence  of  palladium  black. 

Dehydration. — When  alcohols  are  heated  at  400°-500°  in 
the  presence  of  aluminic  oxide  (A1208)  a  decomposition  into 
olefine  and  water  occurs,  no  aldehyde  being  formed.  This 
appears  to  be  a  simple  method  for  obtaining  an  olefine  from 


DEHYDRATION  675 

the  corresponding  alcohol.  It  has  been  shown  that  the  alu- 
minic  oxide  loses  its  activity  when  strongly  heated  and 
rendered  insoluble  in  acids  or  alkalis.  Later  experiments 
have  shown  that  when  the  alcohols  are  heated  under  pressure 
with  the  oxide,  the  primary  decomposition  is  into  water  and 
an  ether,  and  that  at  higher  temperatures  the  ether  yields  an 
olefine  and  water: 

2CH3.CH2.OH  —  (CH3-CH2)2O  +  H2O  (400°) 
(CH3.CH2)20      -«•  2CH2:CH2-fH20      (530°). 

This  reaction  is  characteristic  of  primary  and  secondary  alco- 
hols, and  does  not  occur  in  the  absence  of  the  catalyst,  even 
when  higher  temperatures  are  used.  The  first  reaction  is 
reversible,  as  ether,  under  similar  conditions,  yields  a  certain 
amount  of  alcohol. 

Unsaturated  hydrocarbons  can  also  be  obtained  by  the  action 
of  aluminic  oxide  on  cyclic  alcohols;  thus  menthol  (p.  578) 
yields  menthene.  The  same  catalyst  at  200°-300°  is  able  to 
transform  ethylene  oxide  and  its  homologues  into  the  isomeric 
aldehydes  : 

-  CH3.CH:a 


A  similar  change  occurs  in  the  absence  of  the  catalyst,  but 
at  a  higher  temperature,  viz.  500°-600°.  Bouveault  (Bull.  Soc. 
Chim.  1908  [4],  3,  119)  finds  that  good  yields  of  aldehydes 
can  be  obtained  by  passing  primary  alcohols  over  copper  coils 
heated  by  an  electric  current.  Secondary  alcohols  under 
similar  conditions  '  yield  ketones  and  hydrogen,  and  ketonic 
alcohols,  E.CH(OH).CO-E,  yield  kiketones,  E-CO-CO-E, 
and  hydrogen. 

Unsaturated  alcohols  undergo  molecular  transformation  and 
yield  saturated  aldehydes  : 


Numerous  other  substances,  e.g.  pumice,  animal  charcoal,  sand, 
red  phosphorus,  and  aluminic  phosphate,  can  decompose  alco- 
hols into  olefines  and  water,  but  oxide  of  aluminium  appears 
to  be  the  best  (Senderens,  C.  E.  1907,  144,  381,  1109).  ^  Bou- 
veault  has  designed  a  special  apparatus  for  the  preparation  of 
olefines  by  this  method. 

The  action  of  silica  as  a  catalytic  agent  is  extremely  char- 
acteristic.  Pure  precipitated  silica,  moderately  calcined,  decom- 


676  XLIX.   CATALYTIC  ACTION 

poses  ethyl  alcohol  at  280°,  yielding  pure  ethylene.  After  it 
has  been  more  strongly  calcined,  it  induces  decomposition  only 
at  a  higher  temperature,  and  then  yields  ethylene  and  water 
together  with  hydrogen  and  aldehyde.  Pulverized  quartz  can 
yield  as  much  as  50  per  cent  of  the  theoretical  amount  of 
hydrogen  and  50  per  cent  of  ethylene.  Similarly,  alumina 
which  has  been  strongly  calcined  decomposes  part  of  the 
alcohol  into  hydrogen  and  aldehyde.  Experiments  made  with 
gypsum  (CaS04,  2H20)  dehydrated  below  400°  and  with  an- 
hydrite (CaS04)  indicate  that  the  catalytic  dehydration  of 
alcohols  is  effected  by  substances  which  are  capable  of  forming 
temporary  hydrates.  Thoroughly  calcined  gypsum  or  natural 
anhydrite  decomposes  alcohol  at  high  temperatures  only,  and 
then  yields  mainly  hydrogen  and  acetaldehyde;  on  the  other 
hand,  gypsum  which  has  been  dehydrated  at  a  moderate  tem- 
perature is  capable  of  combining  with  water,  and  decomposes 
alcohol  at  about  400°,  yielding  ethylene  (Senderens,  Bull.  Soc. 
Chim.  1908  [41,  3,  197,  633). 

Sabatier  and  Maihle  (Annales,  1910  [viii],  20,  289)  have 
studied  the  action  of  the  following  metallic  oxides  on  primary 
alcohols,  more  especially  ethanol:  Th02,  A1203,  Cr203,  Si02, 
Ti02,  BeO,  Zr02,  U02,  Mo205,  Fe.O^  V203,  ZnO,  MnO,  CdO, 
Mn304,  MgO.  The  first  four  act  almost  entirely  as  dehy- 
drating agents,  and  at  340°-350°  give  90-100  per  cent  yields 
of  olefine  and  little  or  no  hydrogen.  On  the  other  hand,  the 
last  five  oxides  bring  about  oxidations,  and  give  practically 
100  per  cent  of  hydrogen  and  no  olefine.  BeO  and  Zr02  give 
approximately  equal  volumes  of  hydrogen  and  olefine,  i.e.  they 
are  mixed  catalysers,  as  are  practically  all  the  intermediate 
oxides.  According  to  these  chemists  the  activity  of  finely- 
divided  metals  or  oxides  is  due  to  the  formation  of  unstable 
additive  compounds;  e.g.  in  catalytic  oxidations  of  \mstable 
hydrides : 

Alcohol  4-  metal   — *•  metallic  hydride  +  aldehyde 
Metallic  hydride  — *•  metal  -f-  hydrogen, 

such  hydrides  are  readily  decomposed,  and  yield  the  metal 
which  can  react  with  a  further  quantity  of  alcohol.  With  the 
readily  reducible  metals,  SnO,  CdO,  &c.,  a  small  amount  of 
metal  is  formed,  and  this  reacts  as  above.  As  the  activity 
does  not  increase  with  time,  as  might  be  expected  as  more 
oxide  becomes  reduced,  it  is  suggested  that  the  metal  gradu- 
ally becomes  less  finely  divided  and  hence  less  active.  Oxides 


FORMATION  OF  AMINES  677 

which  are  not  readily  reduced  may  form  unstable  compounds 
with  hydrogen  or  with  the  aldehyde.  The  mechanism  of 
catalytic  dehydration  does  not  consist  in  the  formation  of 
unstable  hydrates  of  the  catalyst  as  at  first  supposed,  but 
in  the  formation  of  alkyl  salts,  formed  by  the  union  of  the 
alcohol  with  the  acidic  oxide  used  as  catalyst: 

ThO2  +  2EtOH  -*  ThO(OEt)2  +  H2O 
ThO(OEt)2  ->  2C2H4-f  ThO(OH)2 

ThO(OH)2  —  Th02  +  H20. 

Esterification.—  Sdbatier  and  Maihle  (C.  E.  1911,  152,  494) 
have  shown  that  Ti02  is  a  good  catalyst  for  the  conversion  of 
acids  and  alcohols  into  esters.  The  method  is  to  allow  a  mix- 
ture of  molecular  proportions  of  the  vapour  of  the  two  com- 
pounds to  pass  over  a  column  of  the  diDxide  kept  at  290°-300°. 
The  yield  of  ester  is  about  70  per  cent,  and  the  process  is 
extremely  rapid.  A  similar  method  may  be  used  for  hydro- 
lysing  esters,  e.g.  allowing  a  mixture  of  the  ester  vapour  with 
an  excess  of  steam  to  pass  over  the  dioxide  at  280° -300°. 
Similar  results  are  obtained  with  thorium  oxide,  provided 
aromatic  acids  are  used. 

Formation  of  Amines,  Thiols,  Ketones. — Amines  are  formed 
when  a  mixture  of  an  alcohol  and  ammonia  is  passed  over 
thorium  dioxide  at  350°-370°  (C.  E.  1909,  148,  898);  thiols 
(mercaptans)  are  formed  when  a  mixture  of  alcohol  and  hy- 
drogen sulphide  is  passed  over  the  dioxide  at  300°-360°  (C.  E. 
1910,  150,  1217,  1569).  The  yields  are  especially  good  with 
primary  alcohols,  and  even  phenol  gives  a  17-per-cent  yield 
of  thiophenol  at  430°-480°;  and  metallic  sulphides,  especially 
CdS,  at  320°-330°,  decompose  thiols  into  alkyl  sulphides  and 
hydrogen  sulphide.  Ketones  can  be  prepared  by  the  action  of 
acid  anhydrides  or  acids  on  thorium  dioxide  at  400°  (Senderens, 
C.  E.  1909,  149,  213,  995;  1910,  150,  111,  702,  1136).  Simple 
and  mixed  aliphatic  ketones  and  mixed  aromatic  aliphatic 
ketones  have  been  prepared,  the  mixed  ketones  by  using  mix- 
tures of  two  acids.  Aromatic  acids  containing  the  carboxylic 
group  attached  to  the  benzene  nucleus  do  not  react  unless 
mixed  with  an  aliphatic  acid,  but  acids  of  the  type  of  phenyl- 
acetic  do.  The  reaction  probably  consists  in  the  formation 
of  a  salt  and  its  subsequent  decomposition  into  ketone,  cap 
bon  dioxide,  and  water. 

Formic  acid  behaves  somewhat  differently  from  the  other 
fatty  acids  (Sdbatier  and  Maihle,  C.  E.  1911, 152, 1212).  Finely 


67$  1*    tTNSATTTRATIOtf 

divided  Pd,  Pt,  Ni,  Cu,  Cd,  and  ZnO  or  SnO  decompose  it 
into  carbon  dioxide  and  hydrogen.  Ti(X  and  W205  yield 
water  and  carbon  monoxide,  and  Si02,  Zr02,  AlgOg,  &c.,  give 
both  reactions. 


L.  UNSATURATION 

A.  Types  of  Unsaturation. — Unsaturated  compounds  are 
usually  defined  as  those  which  are  capable  of  uniting  with 
another  substance  (element  or  compound)  without  disruption 
of  their  original  structure.  Two  main  types  of  such  com- 
pounds have  been  dealt  with  in  the  previous  chapters. 

I.  Cases   in  which  the  addenda  unite  with  two  different 
atoms  of  the  original  compound.     Such  are  the  compounds 
supposed  to  contain  double  or  triple  linkings  between  C  and 
C,  C  and  0,  0  and  S,  C  and  N,  N  and  N,  as  seen  in  the 
groups  of  olefine  and   acetylene   derivatives,   carbonyl   com- 
pounds, thiocarbonyl  derivatives,  nitriles  and  Schiff's  bases, 
azo-com  pounds. 

II.  Cases  in  which  the  addenda  unite  with  one  and  the 
same  atom  of  the  original  compound,  as  in  the  conversion  of 
amines  into  salts  and  quaternary  ammonium  compounds,  the 
formation  of  oxonium  salts  from  ethers,  &c.,  and  the  formation 
of  sulphonium  salts  from  alkyl  sulphides. 

The  presence  of  such  unsaturated  groups  as  amino  and 
hydroxyl,  and  also  the  alkylated  groups,  -NHK,  'NK2,  .OR, 
produce  marked  effects  on*  the  properties  of  the  compounds 
into  which  they  are  introduced.  In  the  aromatic  series  they 
render  the  compounds  much  more  reactive  towards  reducing, 
oxidizing,  and  substituting  reagents  (cf.  p.  409).  When  fur- 
ther substituents  are  introduced,  e.g.  Cl,  Br,  S03H,  N02,  &c., 
these  almost  invariably  take  the  ortho  and  para  positions 
with  respect  to  the  unsaturated  group.  These  groups  also 
tend  to  make  the  compound  luminesce  under  the  influence 
of  electric  discharges  under  small  pressures.  They  are  also 
the  most  powerful  auxochromes  known;  i.e.  when  introduced 
into  a  compound  containing  chromophores,  such  as,  'N:N, 
C:0,  C:C,  N02,  &c.,  they  produce  a  deepening  of  the  colour 
of  the  compound. 

In  examples  of  the  first  type  the  question  as  to  whether 
addition  or  not  takes  place  depends  upon  a  variety  of  factors. 


PROPERTIES  OF  UNSATURATED  ACIDS  679 

(1)  Whether  the  double  linking  is  between  C  and  C,  C  and  0, 
C  and  N,  or  N  and  N.  Thus  although  both  olefines  and 
carbonyl  derivatives  combine  with  hydrogen,  the  first  group 
adds  on  bromine  readily,  whereas  the  second  does  not;  and 
the  second  combines  with  hydrogen  cyanide  or  sodium  bi- 
sulphite more  readily  than  the  first  group  does.  (2)  The 
nature  of  the  groups  already  attached  to  the  two  atoms  which 
are  united  by  the  double  linking.  Thus  although  most  olefine 
derivatives  combine  with  bromine,  compounds  in  which  there 
are  several  negative  groups,  such  as  Ph,  Br,  CN,  C02H, 
already  attached  to  the  two  carbon  atoms,  do  not  form  addi- 
tive compounds  with  bromine  (Hugo  and  Bauer,  B.  37,  3317), 
although  they  contain  an  olefine  linking.  (3)  The  nature  of 
the  addenda.  It  has  been  pointed  out  already  (p.  44)  that 
chlorine  combines  most  readily  and  iodine  least  readily,  but 
that  hydrogen  iodide  combines  more  readily  than  hydrogen 
chloride  or  bromide.  (4)  Conditions  of  the  experiment,  e.g. 
nature  of  solvent,  sunlight,  temperature,  presence  of  a  catalyst, 
&c.  Phenyl-propiolic  acid  does  not  combine  with  hydrogen 
chloride  when  in  aqueous  solution  below  80°. 

B.  Properties  of  TTnsaturated  Acids  as  affected  by  the 
position  of  the  Double  Bond. — Acids  which  contain  a  double 
bond  in  the  a/3  position  differ  in  many  respects  from  isomeric 
acids  in  which  this  bond  is  further  removed  from  the  car- 
boxylic  group. 

The  (ip  unsaturated  acids  are  reduced  much  more  readily 
than  their  isomerides  by  sodium  amalgam  and  water.  This 
is  somewhat  remarkable,  since  in  the  case  of  other  additive 
reactions,  for  example,  the  addition  of  bromine,  the  aj3  un- 
saturated acids  are  less  reactive,  i.e.  do  not  combine  with 
bromine  so  readily  as  /3y  unsaturated  acids  or  other  acids 
in  which  the  double  bond  is  far  removed  from  the  carboxyl 
group  (Sudborvugh  and  Thomas,  J.  C.  S.  1910,  715,  2450).  The 
readiness  with  which  aft  unsaturated  acids  can  be  reduced 
may  perhaps  be  accounted  for  by  the  presence  of  the  con- 
jugated double  bonds  (cf.  p.  681) — 

R.CH:CH.C:6  +  2H  —  R.CH2.CH:C.OH  -*•  R.CH2.CH2.C:O 
OH  OH  OH 

1:4  addition  takes  place,  but  the  resulting  unsaturated  glycol 
is  unstable  and,  by  a  wandering  of  an  atom  of  hydrogen,  yields 
the  saturated  acid. 


680  L.   UNSATURATION 

/.  Bougault  (C.  E.  1905,  i.  9)  shows  that  /3y  unsaturated 
acids  combine  with  the  elements  of  hypoiodous  acid  (HIO), 
yielding  lactones,  whereas  the  isomeric  a/3  acids  do  not.  This 
provides  the  basis  of  a  method  for  separating  a  mixture  of  an 
a/3  and  /3y  unsaturated  acid. 

One  of  the  best  methods  of  separating  a  mixture  of  a/3  and 
/3y  unsaturated  acids  is  due  to  Fittig  (B.  1894,  27,  2667:  A. 
1894,  283,  51),  and  consists  in  heating  the  acids  for  a  few 
minutes  at  140°  with  a  mixture  of  equal  volumes  of  concen- 
trated sulphuric  acid  and  water.  The  a/3  acid  is  unaffected 
by  this  treatment,  whereas  the  /3y  acid  is  converted  into  a 
y-lactone  (p.  217)  which  is  insoluble  in  sodium  carbonate 
solution. 

(CH3)2C:CH.CH2.CO.OH  — 

When  this  method  is  used  only  the  a/3  acid  can  be  re- 
covered. A  method  by  means  of  which  both  acids  can  be 
recovered  is  the  separation  by  fractional  esterification,  as  an 
a/3  acid  is  esterified  much  less  readily  than  isomeric  unsatu- 
rated acids  (Sudborough  and  Thomas,  J.  C.  S.  1911,  2307). 

One  of  the  best  methods  for  determining  the  position  of  the 
double  bond  in  the  case  of  an  olefine  acid  is  by  an  examination 
of  the  oxidation  products  (p.  162).  These  consist,  as  a  rule, 
of  a  mixture  of  a  monobasic  and  a  dibasic  acid,  as  the  carbon 
atoms  between  which  the  olefine  bond  functionated  both  yield 
carboxylic  groups;  e.g.  K'CH:CH.CH2.C02H  gives  K-C02H 
and  C02H.CH2.C02H.  Cf.  also  Oleic  acid,  p.  165. 

Dimethylacrylic  acid,  (CH3)2C :  CH  •  C02H,  when  oxidized 
yields  acetone,  (CH3)2CO,  and  oxalic  acid  or  its  oxidation 
product  carbonic  acid. 

The  conversion  into  ozonides  and  the  decomposition  of  these 
(p.  624)  is  also  used  for  the  determination  of  the  position  of 
the  double  linking. 

Another  method  adopted  for  determining  the  position  of  an 
olefine  bond  is  by  an  examination  of  the  hydrobromide.  If 
the  bond  is  in  the  a/3  position  the  bromo-derivative  of  the 
saturated  acid  loses  hydrogen  bromide  when  treated  with 
alkali  and  yields  the  original  olefine  acid. 

CH3.CH:CH.C02H  — *  CH3.CHBr.CH2.C02H 

Crotonic  acid  /3-Bromobutyric  acid 

—  CH3.CH:CH.C02H. 

Crotonic  acid. 


CONJUGATE  DOUBLE  BONDS  681 

A  /3y  or  78  unsaturated  acid  also  yields  a  hydrobromide, 
but  when  this  is  treated  with  alkalis  hydrogen  bromide  is 
eliminated  and  a  lactone  formed. 

CHS.CH:CH.CH2.CO2H 


The  presence  of  olefine  linkings,  as  in  maleic  anhydride,  in- 
creases to  an  appreciable  extent  the  readiness  with  which  the 
anhydride  combines  with  water  (Eweit  and  Sidgwick,  J.  C.  S. 
1910,  1677). 

An  extremely  simple  method  of  determining  whether  the 
double  bond  is  in  the  a/2  position  or  not,  is  by  an  examination 
of  the  rate  of  esterification  of  the  unsaturated  acid  and  of 
its  saturated  analogue  by  the  catalytic  method.  If  the  un- 
saturated acid  has  a  much  lower  rate  of  esterification  than  its 
reduction  product  the  conclusion  may  be  safely  drawn  that 
the  double  bond  is  in  the  a/2  position,  as  /3y  unsaturated 
acids  are  esterified  somewhat  more  quickly  than  their  satu- 
rated analogues,  and  acids  in  which  the  double  bond  is  still 
further  removed  from  the  carboxyl  group  have  much  the 
same  esterification  constants  as  the  corresponding  saturated 
acids  (Sudborough  and  Gittins). 

For  the  stereochemistry  of  compounds  containing  only  one 
ethylene  linking,  cf.  p.  243.  When  two  or  more  olefine  bonds 
are  present  in  the  molecule,  the  isomerism  is  more  complex. 
Not  merely  can  we  have  structural  isomerides,  which  differ  in 
the  relative  positions  of  the  olefine  linkings,  but  also  the  num- 
ber of  stereoisomerides  increases. 

For  compounds  of  type,  Cab:C:Cab,  see  p.  634. 

C.  Compounds  with  Conjugate  Double  Bonds.  —  One  of  the 
most  interesting  groups  containing  two  double  linkings  are  the 
compounds  with  conjugate  double  bonds.  Within  recent  years 
numerous  experiments  have  been  made  with  compounds  con- 
taining two  double  bonds  in  the  relative  positions  indicated  by 
the  formula  — 

E.CH:CH.CH:CH.E. 

These  have  been  termed  conjugated  double  bonds  by  Thiele, 
and  extremely  interesting  results  have  been  obtained  by  the 
study  of  the  additive  reactions  of  such  compounds.  It  is 


and 


682  L  tJNSATtJRATtotf 

found  that  the  atoms  or  radicals  added  on  do  not,  as  a  rule, 
become  simply  attached  to  the  carbon  atoms  1  and  2  or  3  and 
4,  but  to  numbers  1  and  4;  so  that  a  new  ethylene  linkage  is 
created  in  position  2 : 3.  Thus  cinnamylideneacetic  and  cinna- 
mylidenemalonic  acids  when  reduced  yield  l:4-dihydro-deriva- 
tives  (Ruber,  B.  1904,  37,  3120)— 

C8H6.CH:CH.CH:CH.C02H  +  2H 

-*  C6H6.CH2.CH:CH.CH2.C02H 

C6H6.CH:CH.CH:C(C02H)2  +  2H 

-*  C6H5.CH2.CH:CH.CH(C02H)2. 

Sorbic  acid  (p.  166)  yields  CH3.CH2.CH:CH.CH2.C02H: 
similarly  butadiene,  CH2 :  CH  •  CH :  CH2,  reacts  with  bromine, 
yielding  l:4-dibromo-A2:3-butene,  CH2Br .  CH  :  CH .  CH2Br. 
Similar  results  have  been  obtained  when  the  double  bonds 
are  between  carbon  and  oxygen;  thus  benzil, 

6:C(C6H6).C(C6H6):6, 

when  reduced  under  special  conditions  yields  OH«C(C6H6): 
C(C6H5)-OH  a/3-dihydroxy-stilbene. 

That  additions  do  not  always  take  place  in  the  1 : 4-positions 
is  shown  by  the  following  examples:  Methyl  cinnamylidene- 
malonate  adds  on  bromine  in  the  3: 4-positions  and  yields 
C6H5  •  CHBr  •  CHBr .  CH :  C(C02Me)2  (Henrichsen  and  Triepel, 
A.  1904,  336,  223).  The  addition  of  potassium  hydrogen  sul- 
phite to  cinnamylidenemalonic  acid  occurs  in  the  1 : 2-position, 
and  the  product  is — 

C6H6  •  CH :  CH  •  CH(SOSK) .  CH(C02H)2 

(Kohler,  Am.  1904,  31,  243);  similarly  with  hydrogen  cyanide. 
Unsaturated  aldoximes  and  ketoximes  when  reduced  yield  un- 
saturated  amines,  indicating  that  the  addition  of  hydrogen — 

K-CHiCH-CHiN-OH  -f  4H 

— +  R.CH:CH.CH2-NH2-f  H2O 

occurs  in  the  1: 2-position  (Harries,  A.  1903,  330,  193);  a/3 
unsaturated  ketones  also  add  on  sulphinic  acids  in  the  1:2 
(carbonyl)  position  (Am.  1904,  31,  163).  s-Diphenylbuta- 
diene,  CHPh:CH«CH:CHPh,  also  adds  on  bromine  in  the 
1 : 2-position. 

Thick  (A.  1889,  306,  87)  has  attempted  to  account  for  the 


DIVALENT  CARBON  683 

characteristic  l:4-addition  of  most  of  the  compounds  with 
conjugated  double  bonds  by  his  theory  of  partial  valencies. 

It  is  supposed  that  when  two  atoms  are  united  by  a  double 
bond  the  whole  of  the  energy  of  the  atoms  is  not  used  up,  but 
that  there  is  a  slight  residual  affinity  or  partial  valency  which 
Thiele  denotes  by  dotted  lines,  e.g.\ 

ECH:CHK. 


He  considers  the  power  of  forming  additive  compounds  is  due 
to  the  presence  of  such  partial  valencies. 

Now  in  a  system  with  two  double  bonds  in  positions  1:2 
and  3:4  there  are  four  partial  valencies,  and  according  to 
Thiele  two  of  these,  viz.  2  and  3,  are  supposed  to  have  neu- 
tralized one  another  and  only  1  and  4  are  active.  This  is 
usually  represented  by  the  formula — 

K.CH:CH.CH:CH.K, 

and  hence  the  usual  1 : 4-addition  with  compounds  containing 
conjugated  double  bonds.  Thiele's  theory  does  not  account  for 
the  numerous  exceptions  mentioned  above. 

Probably  it  is  simpler  to  regard  the  compound  as  containing 
4  residual  valencies  in  the  1,  2,  3,  4  positions,  and  to  conclude 
that  the  question  as  to  which  of  these  will  be  used  up  in  the 
formation  of  an  additive  compound  depends  largely  on  the 
nature  of  the  addenda  and  the  nature  of  the  groups  already 
attached  to  the  atoms  numbered  1,  2,  3,  and  4. 

The  reaction  between  compounds  with  conjugated  double 
bonds  and  Grignard's  reagents  consists  in  many  cases  of  1:4- 
addition.  See  Kohler  (Am.  1904,  31,  642;  1905,  33,  21,  35, 
153,  333;  34,  568;  1906,  35,  386;  36,  177,  529;  1907,  37, 
369;  38,  511;  1910,  43,  412,  475). 

D.  Compounds  of  Di-  and  Trivalent  Carbon.  —Carbon 
monoxide  may  be  written  either  as  C:0  or  CjO.  In  the 
first  formula  both  carbon  and  oxygen  atoms  are  represented 
as  being  divalent,  and  in  the  latter  formula  both  are  tetra- 
valent.  It  has  been  argued  that  the  formula,  C:0,  is  prob- 
ably the  correct  one,  as  when  the  monoxide  forms  additive 
compounds  the  two  addenda  become  attached  to  carbon 
and  not  one  to  carbon  and  one  to  oxygen.  Thus  with 

chlorine  we  get  carbonyl  chloride,  0:C<CQj,  the  constitution  of 


684  L.   tJNSATURATION 

which  is  determined  by  the  fact  that  it  reacts  with  alcohol, 
forming  ethyl  chloro-carbonate  and  finally  ethyl  carbonate, 
0:C(OEt)2.  With  sodium  hydroxide  carbon  monoxide  gives 
rise  to  sodium  formate: 

0:C-hNaOH  =  O:C 

and  with  hydrogen  chloride  it  yields  the  unstable  formyl 
chloride,  OlCxpi.  Although  vapour-density  determinations 


indicate  that  in  a  mixture  of  the  two  gases  very  little  com- 
bination has  taken  place,  yet  Gattermann 's  synthesis  of  acid 
chlorides,  by  the  action  of  a  mixture  of  carbon  monoxide  and 
hydrogen  chloride  on  aromatic  compounds  in  the  presence 
of  aluminium  chloride,  proves  that  a  small  amount  of  an  addi- 
tive compound  exists,  and  that  its  structural  formula  is  the 
one  represented  above. 

Carbylamines. — On  p.  104  the  conclusion  has  been  drawn 
that  in  the  carbylamines  (alkyl  isocyanides)  the  alkjd  group 
must  be  attached*  to  nitrogen  and  not  to  carbon,  and  therefore 
they  are  to  be  represented  as  R-N-C  or  R»N:C.  In  the 
latter  formula  the  carbon  atom  is  represented  as  being  di- 
valent, and  the  arguments  used  in  support  of  this  formula  are 
similar  to  those  used  in  the  case  of  carbon  monoxide,  viz.  the 
two  addenda  invariably  unite  with  the  carbon  atom  and  not 
one  with  carbon  and  one  with  nitrogen.  The  following  ex- 
amples can  be  given: — (a)  with  chlorine:  RN:CC19;  (b)  with 

/COPh 
acyl  chlorides:  R«N:C<\™        ;   (c)  with  hydrogen  sulphide: 

R-NrCH.SH  =  R.NH-CH:S  (an  alkylated  thioformamide) ; 
(d)  with  oxygen:  R»N:C:0,  alkyl  isocyanates;  (e)  with  sul- 
phur: R-N:C:S,  mustard  oils;  (/)  with  Grignard  reagents: 

T?  ttf'C*/'         — ».  ~R  "Nr-r*^ 
N'C\MgI  n.,0  E  N'C\H' 

an  imino- derivative  which  is  hydrolysed  to  an  aldehyde, 
0:CH.R;  (g)  with  ethyl  hypochlorite.  Cf.  Nef,  A.  287,  273. 
Metallic  Cyanides. — Both  nitriles  and  carbylamines  are 
alkyl  derivatives  of  hydrogen  cyanide,  and  can  be  obtained 
by  the  action  of  alkyl  iodides  or  potassium  alkyl  sulphates  on 
different  metallic  cyanides,  e.g.  potassium  cyanide  and  ethyl 
iodide  yield  ethyl  cyanide,  whereas  the  same  iodide  with 
silver  cyanide  yields  mainly  ethyl  carbylamine.  Although 
two  series  of  alkyl  derivatives  exist>  only  one  hydrogen 


METALLIC  CYANIDES  685 

cyanide  is  known.  Certain  of  its  reactions  point  to  the  nitrile 
structure  H-C-N,  and  others  to  the  carbylamine  formula 
H«N:C;  it  is  a  typical  tautomeric  substance.  The  view  gene- 
rally held  with  regard  to  the  metallic  cyanides  is  that  they 
have  a  carbylamine  structure.  The  arguments  used  are  briefly 
as  follows:  —  (1)  The  similarity  between  the  additive  reactions 
of  metallic  cyanides  and  those  of  carbylamines  (a)  with 
bromine  potassium  cyanide  yields  potassium  bromide  and 
cyanogen  bromide;  although  an  additive  compound  cannot 
be  isolated,  the  reaction  is  in  complete  harmony  with  the  view 
that  an  unstable  compound, 


is  formed  which  breaks  up  into  KBr  and  N  •  C  •  Br;  (b)  po- 

tassium cyanide  and  benzoyl  chloride  yield  benzoyl  cyanide, 
N  •  C  •  CO  •  CgH5,  but  here  again  an  additive  compound, 
K  •  N  :  CC1  •  COC6H5,  is  probably  first  formed;  (c)  potassium 
cyanide  combines  with  oxygen  and  sulphur  in  much  the  same 
manner  as  the  carbylamines;  (d)  with  ethyl  hypochlorite  a 
compound,  HN  :  C(OEt)  •  CN,  ethyl  cyano-imino-  carbonate,  is 
formed.  The  reaction  can  be  represented  as  follows:  — 


K-NiC  —  K-NiCCl-OEt          K-N:C(OEt).CCl:NK 

-*  KCl  +  K.N:C(OEt).CN. 

(2)  Both  alkyl  carbylamines  and  alkali  cyanides  dissolve 
silver  cyanide  yielding  double  salts,  whereas  alkyl  cyanides 
do  not.  (3)  Tetramethylammonium  cyanide,  which  probably 
has  a  constitution  similar  to  that  of  the  metallic  cyanides, 
yields  trimethylainine  and  methylcarbylamine  when  heated. 
This  last  argument  by  itself  is  of  but  little  value,  as  a  com- 
paratively high  temperature  is  required  and  molecular  rear- 
rangements could  occur. 

Reactions  of  Metallic  Cyanides.  Formation  of  Nitriles 
and  Carbylamines.  —  The  following  reactions  occur:  — 

HI 

'->.':.  .  -,       —  -     alkyl  cyanides,  K-C:N 

Potassium  cyanide     _     acyl  cyanides,  K-  CO-  C:N. 
B-COCl 
£1 

.  ,  —  »•     alkyl  carbvlamines,  E,«N:G 

Silver  cyanide  _     acy{ 

B.-COC1 


686  L.   UNSATURATION 

The  reactions  cannot  be  due  to  the  tautomerism  of  silver 
cyanide,  as  no  cases  are  known  where  a  heavy  atom  like 
silver  can  wander.  The  view  that  carbylamines  are  first 
formed  by  simple  exchange  in  all  cases,  and  then  in  three 
of  the  four  reactions  the  carbylamine  becomes  transformed 
into  a  nitrile,  is  untenable,  as  carbylamines  cannot  be  trans- 
formed into  nitriles.  The  reverse  process  is  also  improbable, 
as  carbylamines  are  formed  from  nitriles  at  high  temperatures 
only. 

The  views  of  Nef(A.  287,  274)  as  modified  by  Wade  (J.  C.  S. 
1902,  1596)  are  that  in  all  four  cases  additive  compounds  are 
first  formed.  When  the  metallic  radical  in  the  cyanide  is 
feebly  positive,  then  feebly  positive  alkyl  compounds  combine 
with  N,  but  negative  acyl  derivatives  combine  with  C.  With 
a  strongly  positive  metallic  atom  in  the  cyanide,  e.g.  KCN, 
both  alkyl  and  acyl  derivatives  combine  with  N.  Thus  with 
AgNC  and  EtI  we  have  addition  to  N.  Similarly  with  EtNC 
and  EtI;  but  with  AgNC  and  AcCl,  and  EtNC  and  AcCl, 
we  have  addition  to  C.  With  KNC  and  EtI  and  also  with 
KCN  and  AcCl  the  addition  is  to  C. 

K-NiC  +  Etl       —  K.N:C<fc    ->  KI-fN:CEt 

Ag.N: 

Ag-N:C-fAcCl  —  Ag-NiCK^0  —  AgCl  +  N-C-Ac. 


It  may  appear  remarkable  that  in  reaction  2  the  alkyl 
iodide  adds  on  to  the  nitrogen  atom  and  leaves  the  carbon 
divalent.  Nef  assumed  that  the  conversion  of  the  silver  salt 
into  carbylamine  was  an  example  of  direct  displacement,  but 
Wade  proves  that  dry  silver  cyanide  is  able  to  absorb  methyl 
iodide  at  its  boiling-point,  yielding  a  viscid  mass  which  evolves 
methylcarbylamine  when  more  strongly  heated.  The  consti- 
tution of  this  additive  compound  is  based  on  a  study  of  the 
products  from  alkyl  iodides  and  aikylcarbylamines  ;  when 
hydrolysed  these  compounds  yield  small  amounts  of  secondary 
amines,  and  hence,  according  to  Wade,  must  be  represented  as: 

Me-N:C 


and  similar  formulae  are  given  to  the  products  from  silver 
cyanide  and  alkyl  iodides. 


METALLIO  CYANIDES  687 

Sidgivick  (P.  1905,  120)  concludes  that  in  all  cases  addition 
takes  place  at  the  carbon  atom: 


where  M  represents  either  K  or  Ag.     Such  a  compound  con- 
tains the  grouping: 


characteristic  of  the  oximes  of  aldehydes  and  of  unsymmetri- 
cal  ketones  (cf.  pp.  137,  428),  and  can  therefore  exist  in  syn- 
and  anti-  configurations.  Potassium  cyanide  is  supposed  to 
yield  the  sytt-compound  : 

E.C.I 


which  readily  loses  potassium  iodide,  as  both  metal  and  halo- 
gen are  on  the  same  side  of  the  molecule,  and  thus  yields 
a  nitrile.  Silver  cyanide,  on  the  other  hand,  yields  the  anti- 
compound: 

E-C-I 

Ag-N. 

Silver  iodide  is  not  readily  split  off,  as  the  metal  and  halogen 
are  now  on  different  sides  of  the  molecule.  It  therefore 
undergoes  the  Beckmann  transformation  (p.  429),  yielding: 

Ag-C.I 
E.N    ' 

which  loses  silver  iodide  and  forms  C:N»E,  an  alkyl  carbyl- 
amine. 

Although  the  metallic  cyanides  are  usually  represented 
by  a  carbylamine  structure,  it  does  not  follow  that  hydrogen 
cyanide  is  to  be  represented  in  a  similar  manner.  Arguments 
based  on  a  study  of  its  physical  and  chemical  properties  have 
been  brought  forward;  some  point  to  the  one,  and  others  to 
the  alternative  formula,  but  probably,  on  the  whole,  the  pro- 
perties are  more  in  harmony  with  the  nitrile  structure,  H»C|N. 
It  is  possible  that  it  may  be,  like  the  tautomeric  substance, 
ethyl  acetoacetate,  a  mixture  of  the  two  compounds  but  mainly 
nitrile.  (For  summary  see  Sidgwick,  "  The  Organic  Chemistry 
of  Nitrogen",  p.  209.) 

J?ulminic  acid,  C  ;  N  •  OH,  is  known  chiefly  in  the  form  of  its 


688  L.    UNSATURATION 

silver  and  mercury  salts.  The  latter  was  first  prepared  in 
1800  by  Howard,  by  the  action  of  alcohol  and  nitric  acid  on 
mercuric  nitrate.  It  crystallizes  in  lustrous  prisms,  explodes 
with  great  violence  when  heated  or  struck,  and  is  largely  used 
in  the  manufacture  of  percussion  caps,  dynamite  cartridges, 
&c.  In  1824  Gay-Lussac  and  Liebig  showed  that  the  silver 
salt  had  the  same  percentage  composition  as  silver  cyanate, 
and  thus  afforded  one  of  the  first  examples  of  isomerism. 
They  also  showed  that  double  salts,  e.g.  KAg(CNO)2,  could 
be  obtained.  Various  formulae  have  been  proposed.  KekuU 
suggested  the  formula  N02»CH2.CN,  riitroacetonitrile;  Holle- 
mann  suggested  a  glyoxime  peroxide  formula, 

CH CH 

N.O-O-N  ; 

and  Steiner  in  1883  the  formula  OH.N:C:C:N.OH,  di-iso- 
nitroso  ethylene.  It  will  be  noticed  that  all  these  formulae 
represented  the  molecule  as  containing  two  carbon  atoms. 
The  reasons  for  this  were:  (1)  It  is  obtained  from  ethyl  alcohol. 
(2)  With  bromine  or  iodine  it  yields  ethane  derivatives.  (3)  As 
it  forms  double  salts  the  acid  was  thought  to  be  dibasic. 
Various  arguments  were  brought  forward  in  favour  of  and 
against  the  first  two  formulae,  but  the  question  has  been 
definitely  decided  by  the  preparation  of  nitroacetonitrile 
(Steinkopf  and  Jjohrmann,  B.  41,  1044)  and  of  glyoxime  per- 
oxide (Jomtschitsch,  A.  347,  233),  and  showing  that  they 
differ  from  fulminic  acid.  The  main  argument  in  favour  of 
Steiner's  formula  is  that  fulminates  yield  hydroxylamine  when 
treated  with  concentrated  hydrochloric  acid,  just  as  V.  Meyer 
had  previously  shown  that  oximes  do.  Steiner  was  able  to 
prove  that  the  whole  of  the  nitrogen  can  be  removed  in  this 
way  in  the  form  of  hydroxylamine,  and  also  that  formic  acid 
is  the  second  product: 

C2H2O2N2  +  4H2O   —  2H2CO2  +  2NH2OH. 

Such  a  reaction  proved  that  KekuU's  formula  could  not  be 
correct. 

In  1894  Nef  (A.  280,  303)  suggested  the  simple  formula 
C:N«OH,  now  generally  accepted,  which  represents  the  acid 
as  the  oxime  of  carbon  monoxide.  The  following  arguments 
were  adduced:  (1)  By  the  action  of  one  equivalent  of  hydrogen 
chloride  on  one  of  the  silver  salt,  no  trace  of  silver  chloride  is 
formed,  but  an  additive  product,  which  was  shown  to  be  the 


FULMINATES  G89 

chloride  of  formhydroxamic  acid,  or  formyl- chloride  oxime, 
C1«CH:N.OH.  This  forms  colourless  crystals  volatile  at  the 
ordinary  temperature,  and  decomposes  readily.  With  aniline 
it  yields  formanilide  oxime,  NHPh.CHrN.QH  or  NPh:CH- 
NH'OH.  (2)  It  can  be  synthesized  from  a  compound  con 
taining  one  carbon  atom,  namely  nitromethane.  The  mercuric 
salt  of  nitromethane,  when  heated  with  water,  yields  water 
and  mercury  fulminate: 

CH2:NO-OM  —  H2O  + C:N.OM. 

(3)  With  nitrous  acid  it  yields  methylnitrolic  acid  (p.  96). 
C:N.OH  +  H.N02  —  NO2-CH:N.OH. 

(4)  According  to  Schott  (B.  32,  3492;  36,  10,  322,  648),  when 
benzene  is  treated  with  mercury  fulminate  and  a  mixture  of 
anhydrous  and  hydrated  aluminium  chloride,  benzaldoxime  is 
formed  (70  per  cent).  The  water  of  the  hydrated  chloride 
liberates  hydrogen  chloride,  which  combines  with  the  fulmi- 
nate, yielding  the  additive  compound,  OM»N:CHC1,  which 
then  condenses  with  the  benzene  in  the  manner  of  the  Friedel- 
Crafts  reaction,  yielding  C6H5«CH:N'OM,  from  which  the 
free  oxime  is  liberated  by  means  of  mineral  acid. 

The  hydrolysis  of  a  fulminate  to  formic  acid  and  hydroxyl- 
amine  by  means  of  hydrochloric  acid  is  almost  undoubtedly 
preceded  by  the  formation  of  an  additive  compound: 

OH.N:CH.C1  +  H2O     —  OH-NzCH-OH 
OH.N:CH.OH  +  H20  _*  O:CH.QH +  NH2OH. 

Free  fulminic  acid  can  be  obtained  by  the  action  of  an  ex- 
cess of  sulphuric  acid  on  a  solution  of  potassium  fulminate  and 
extraction  with  ether.  It  volatilizes  with  the  ether  when  this 
is  distilled,  and  readily  polymerizes  to  meta-fulminic  acid.  Nef 
has  pointed  out  the  remarkable  analogy  between  hydrogen 
cyanide  and  fulminic  acid.  No  direct  estimations  of  the  mole- 
cular weight  of  fulminic  acid  have  been  made,  but  an  indirect 
determination  by  L.  Wohler  (B.  1905,  38,  1351)  points  to  the 
simple  formula  HCNO.  The  method  is  based  upon  the  deter- 
mination of  the  value  of  van't  Hofs  dissociation  factor  i  for  the 
sodium  salt  in  0'2  to  O'l  Absolution.  The  value  was  found  to 
be  1  -85,  the  usual  value  for  the  salt  of  a  monobasic  acid.  Also 
the  increase  in  molecular  conductivity  in  passing  from  N/32  to 
JV/1024  solution  was  found  to  be  5  units,  corresponding  with 
Ostwald's  value  4-8  for  the  salt  of  a  monobasic  acid. 

(B480)  2X 


690  L.   UNSATURATION 

The  following  has  been  suggested  by  Wieland  as  the  prob- 
able course  of  the  reaction  in  the  preparation  of  a  fulminate 
from  ethyl  alcohol:  Oxidation  to  acetaldehyde,  formation  of 
isonitroso  -  acetaldehyde,  oxidation  to  isonitroso  -  acetic  acid, 
HO  •  N :  CH  •  C02H,  nitration  to  nitro-isonitroso-acetic  acid,  de- 
composition into  carbon  dioxide  and  methylnitrolic  acid,  con- 
version of  methylnitrolic  acid  into  nitrous  and  fulminic  acids. 

A  polymer  of  fulminic  acid,  known  as  fulminuric  acid,  has 
been  shown  to  be  cyanonitroacetamide, 

NO2  •  CH(CN)  •  CO .  NHa. 

Tervalent  Carbon:  Triphenyl- methyl. — In  attempting  to 
prepare  hexaphenylethane  by  the  action  of  finely  divided  silver 
or  zinc  on  triphenylchloromethane  in  benzene  solution,  Gom- 
berg  (J.  Am.  1900,  22,  757)  obtained  a  substance  which  con- 
tained oxygen,  but  in  the  absence  of  air  the  product  was  free 
from  oxygen,  and  when  the  solution  was  carefully  evaporated 
a  compound  with  pronounced  unsaturated  properties  was  iso- 
lated. It  combines  vigorously  with  oxygen,  yielding  the 
peroxide,  CPhg-O-O-CPhg,  m.-pt.  185°-186°,  which  is  trans- 
formed  by  sulphuric  acid  into  triphenylcarbinol ;  it  also  com- 
bines with  iodine,  yielding  triphenyliodomethane,  and  forms 
additive  compounds  with  ethers,  ketones,  esters,  nitriles,  &c. 
It  was  suggested  that  these  properties  pointed  to  the  formula, 
CPh3,  for  the  hydrocarbon,  a  formula  which  contains  a  ter- 

valent  carbon  atom.  The  corresponding  ion,  CPh3,  appears  to 
be  formed  when  triphenylchloromethane  is  dissolved  in  liquid 
sulphur  dioxide,  as  such  solutions  are  good  conductors  of  the 
electric  current.  Molecular  weight  determinations  by  the  cryo- 
scopic  method  point  to  the  double  formula,  (CPh3)2,  for  the 
hydrocarbon.  Tschitschabin  (B.  37,  4709)  has  suggested  that  the 
product  is  hexaphenylethane,  and  has  supported  this  conclusion 
by  a  study  of  the  properties  of  pentaphenylethane,  which  is 
somewhat  unstable  and  readily  attacked  by  oxygen,  and  is 
completely  ruptured  by  hydrochloric  acid  at  150°.  Quinonoid 
formulae  have  also  been  suggested,  the  symmetrical  formula  I 
by  Heintschel  (B.  36,  320,  579),  and  formula  II  by  Jacobson 
(B.  37,  196): 

(I)  CPh2:0<g|:™>CH.CH<™:gg>C:CPh2 
(II) 


KETENS  691 

According  to  Schmidlin  (B.  41,  2471)  two  forms  of  triphenyl- 
methyl  exist,  a  colourless  and  a  yellow.  When  freshly  dis- 
solved in  benzene  the  solution  is  colourless  but  changes 
gradually  to  orange-yellow.  The  colour  is  destroyed  by 
shaking  the  solution  with  air,  but  returns  again  on  standing, 
and  it  is  argued  that  the  yellow  form  reacts  with  air  more 
readily  than  the  colourless  compound.  In  solution  there  is  an 
equilibrium  between  the  colourless  and  coloured  forms,  and 
the  equilibrium  is  displaced  in  favour  of  the  colourless  by 
lowering  the  temperature.  The  general  view  is  that  the 
equilibrium  may  be  represented  by  the  equation: 

CPh3.CPhs  ^±  2CPh3; 
Colourless  Yellow 

and  this  view  is  supported  by  Wieland  (B.  42,  3020),  who 
shows  that  in  naphthalene  solution,  which  contains  more  of 
the  yellow  form  than  the  benzene  solution  does,  the  molecular 
weight  is  much  less  than  that  required  by  the  formula  (CPh3)2, 
indicating  that  the  yellow  compound  presumably  has  the  com- 
position CPh3.  Schlenk,  Weickel,  and  Herzenstein  (A.  372,  1) 
have  prepared  a  tri-diphenylmethyl,  C(C6H4«C6H6)3,  by  the 
action  of  finely  divided  copper  on  tri-diphenylchloromethane, 
and  have  been  able  to  show  that  in  solution  it  is  monomole- 
cular.  The  corresponding  bimolecular  form  is  not  known. 
Its  solutions  have  a  deep-violet  colour,  and  it  reacts  readily 
with  oxygen,  giving  a  colourless  peroxide.  Corresponding 
diphenyl-diphenylmethyl,  CPh2  •  C6H4  •  Ph,  and  phenyl-di 
diphenylmethyl,  CPh(C6H4'Ph)2,  have  been  prepared;  they 
exist  in  both  coloured  and  colourless  modifications. 

Just  as  colourless  hexaphenylethane  tends  to  break  up  into 
coloured  triphenylmethyl,  so  pentaphenylethane  when  heated 
in  anisole  solution  in  absence  of  air  breaks  up  into  CPh3 
(yellow)  and  CHPh2 ;  the  formation  of  the  latter  is  proved  by 
the  formation  of  tetraphenylethane  due  to  the  union  of  two 
CHPh2  radicals. 

E.  Ketens.— Wilsmore  (J.  C.  S.  1907,  91,  1938;  1908,  93, 
946)  has  isolated  the  simplest  possible  ketone,  CH2:CO,  which 
he  terms  keten,  and  which  may  be  regarded  as  a  new  [anhy- 
dride of  acetic  acid.  It  is  obtained  by  the  action  of  a  hot  pla- 
tinum wire  on  acetic  anhydride;  numerous  other  substances 
are  formed  at  the  same  time,  but  a  10-per-cent  yield  is  obtained. 
It  is  a  colourless  gas  at  the  ordinary  temperature,  has  a  char- 
acteristic odour,  and  reacts  with  hydrogen  chloride,  ammonia, 


692  L.    UNSATURATION 

and  aniline,  yielding  acetyl  chloride,  acetamide,  and  acetanilide 
respectively.     When  kept  for  some  time  it  polymerizes,  yield- 

ing cyclohutane-l:3-dione,  CH2<^Q>CH2,  b.-pt.  126°-127°, 

which  combines  with  water  to  acetoacetic  acid  (p.  226),  and 
with  aniline  to  acetoacetanilide  (J.  C.  S.  1910,  1978). 

Homologues  of  keten,  e.g.  dimethyl-keten,  (CH3)2C  :  CO,  and 
diphenyl-keten,  (C6H5)2C:CO  (Staudinger,  B.  1905,  38,  1735; 
1906,  39,  968;  1907,  40,  1145,  1U9),  have  also  been  prepared. 
The  method  consists  in  the  action  of  zinc  on  a-bromoisobutyryl 
bromide  and  diphenyl-chloroacetyl  chloride  respectively.  The 
compounds  are  unstable  and  readily  polymerize.  Dimethyl- 
keten  forms  stable  compounds  with  tertiary  amines,  and  with 
water,  alcohol  or  amines  give  isobutyric  acid,  its  ester  or 
amide  : 

CMe2C:CO  +  HX  — 


The  presence  of  a  keten  group,  •CHg'CO',  is  of  great  impor- 
tance in  the  syntheses  of  numerous  cyclic  compounds  (cf.  Collie, 
J.  C.  S.  1907,  91,  1806). 

The  homologues  are  frequently  divided  into  (a)  aldoketens, 
(b)  ketoketens.  The  aldo  group  comprises  keten,  its  mono- 
alkyl  substituted  derivatives,  and  carbon  suboxide.  They  are 
colourless,  incapable  of  autoxidation,  and  are  polymerized  by 
pyridine.  The  keto  group  consists  of  the  dialkylated  deriva- 
tives. These  are  coloured,  readily  undergo  autoxidation,  and 
form  additive  compounds  with  tertiary  amines,  such  as  pyri- 
dine, quinoline,  and  acridine.  These  products  from  dialkyl 
ketens  and  tertiary  amines  are  stable  and  have  basic  pro- 
perties; they  contain  two  molecules  of  keten  combined  with 
one  of  the  base,  and  the  compound  with  quinoline  is  repre- 
sented  as  H 


CH 


CO.CMe2.CO-CMe2 

(A.  1910,  374,  1).  They  also  form  additive  compounds  with 
substances  containing  the  groupings  C:N  and  C:0,  for  ex- 
ample Schifs  bases  and  quinones.  Diphenyl  keten  and  qui- 


none  yield  the  /3-lactone,  0  :  C6H4CO,  which  decom- 


poses into  C02  and  0  :  C6H4  :  CPhg,  diphenyl-quinomethane, 
when  heated  (Staudinger,  B.  1908,  906,  1355,  H93). 


tJNSATtJRATION   AND   PHYSICAL  PROPERTIES  603 

Ethyl  ethylketene-carboxylate,  C02Et-CEt:CO,  is  colour- 
less, and  does  not  yield  additive  compounds,  but  readily  poly- 
merizes, yielding  a  cyclobutane  derivative. 

F.  Unsaturation  and  Physical  Properties. — Unsaturation, 
especially  in  the  case  of  compounds  with  conjugate  linkings, 
produces  a  marked  effect  on  numerous  physical  properties. 
The  phenomena  which  have  been  most  closely  studied  are 
those  on  the  refraction  and  dispersion  of  light.  The  effect 
of  such  a  conjugate  linking  as  in  CHMe :  CH  •  CH :  CHMe,  is 
to  produce  a  considerable  increase  or  exaltation  in  the  specific 
and  molecular  refraction  and  dispersions.  In  the  case  men- 
tioned the  molecular  refraction  is  about  one  unit  greater  than 
the  value  calculated  from  the  atomic  refractions  -f-  two  olefine 
linkings.  The  existence  of  such  exaltation  is  frequently  used 
as  an  argument  in  favour  of  the  presence  of  conjugate  link- 
ings (either  two  olefine  or  an  olefine  and  carbonyl)  in  the  com- 
pound examined.  In  the  case  of  hexatriene,  CH2:CH«CH: 
CH '011:0112,  the  exaltation  is  2*06  units.  Exaltation  is  also 
observed  when  an  acetylene  linking  is  in  conjugation  with  a 
carbonyl  group.  According  to  Moureau  (Annales,  1906,  [8], 
7,  536),  and  Muller  and  Bauer  (J.  Chim.  Phys.  1903,  1,  190), 
the  exaltation  in  certain  series  of  compounds  increases  with 
the  negative  character  of  the  substituents.  Little  or  no 
exaltation  is  met  with  in  the  case  of  benzene,  furane,  diacetyl, 
and  similar  compounds,  although  the  formulae  usually  written 
for  these  compounds  contain  conjugate  bonds.  This  may  be 
due  to  special  symmetrical  ring  structure  or  to  mutual  neutrali- 
zation of  residual  affinities.  Unsaturated  groups  such  as  amino, 
vinyl  and  allyl,  when  present,  in  benzene  compounds  and 
directly  attached  to  the  nucleus,  produce  exaltation,  probably 
owing  to  a  readjustment  of  residual  affinity.  Exaltation  is 
extremely  well  marked  in  compounds  containing  conjugate 
linkings,  which,  in  their  turn,  are  conjugate  to  the  ethylene 
bonds  in  phenyl  groups:  e.g.  diphenyl-butadiene,  CHPh:CH« 
CHiCHPh,  has  an  exaltation  of  15  units  (Klages,  B.  40,  1768); 
cinnamylideneacetic  acid,  CHPh :  CH  •  CH :  CH  •  C(OH) :  0,  of 
10-5  units,  and  diphenyl-hexatriene,  CHPh:CH.CH:CH.CH: 
CHPh,  of  24  units  (Smedley,  J.  0.  S.  1908,  376). 

Some  of  the  most  accurate  work  on  unsaturated  compounds 
has  been  carried  out  by  Auwers  and  Eisenlohr  (J.  pr.  82,  65; 
84,  1,  37).  They  compare  the  specific  refractions  x  100,  and 
not  molecular  refractions,  and  make  use  of  the  following  values 
for  atomic  refractions  nD  as  determined  by  Eisenlohr  (Zeit. 


694         LI.    ALIPHATIC  DIAZO   ANt>  TRlAZO-COMPOtrfcDS 

75,  585):  CH2  =  4-618,  C  =  2-418,  H  =  1,  O  (in  car 
myl)  =  2-211,  0  (in  ethers)  =  1-643,  0  (in  hydroxyl)  = 
1-525,  Cl  =  5-967,  Br  =  8-865,  I  =  13-900,  define  linking 
=  1-733,  and  acetylene  linking  =  2*398.  They  find  that  a 
single  conjugation  in  a  hydrocarbon  produces  an  exaltation 
of  approximately  1*9  units,  but  that  this  value  is  reduced  to 
an  appreciable  extent  by  the  introduction  of  substituents. 
The  amount  of  this  interference  depends  upon  the  number 
and  position  of  the  substiuients.  In  cinnamene  and  its  /?-sub- 
stituted  derivatives  the  exaltation  is  about  TO,  and  when 
three  substituents  are  present  the  exaltation  is  only  0-45. 
They  conclude  that  for  a  given  type  of  compound  the  exalta- 
tion is  fairly  constant,  and  within  such  limits  the  existence 
of  the  exaltation  may  be  made  use  of  in  discussions  bearing 
on  constitution. 

When  several  pairs  of  conjugate  linkings  are  present,  it  is 
found  that  the  exaltation  is  much  greater  when  these  all  form 
a  single  chain  (cf.  hexatriene)  than  when  they  are  "  crossed  " 


as  in 


Semicyclic  double  bonds  (p.  574)  and  rings  formed  of  three 
atoms,  e.g.  trimethylene,  also  produce  optical  exaltation. 

For  effects  of  unsaturation  on  heats  of  combustion,  see 
Auwers  and  Roth  (A.  373,  239,  267). 

For  effects  of  unsaturation  on  optical  activity,  see  Frank- 
land  and  others,  J.  C.  S.  1906,  1854,  1861;  1911,  2325; 
Hildich,  J.  C.  S.  1908,  1,  700,  1388,  1618;  1909,  331,  1570, 
1578;  1910,  1091;  1911,  218,  224;  Zeit.  phys.  1911,  77,  482; 
Rupe,  A.  373,  121. 


LI.  ALIPHATIC  DIAZO-  AND  TEIAZO-COM POUNDS 

A.  Diazo-compounds. — By  the  action  of  nitrous  acid  on  a 
solution  of  a  salt  of  a  primary  aromatic  amine,  the  important 
group  of  diazo  or  diazonium  salts  are  formed.  It  is  generally 
stated  that  aliphatic  amino-compounds  differ  from  the  aromatic 
in  this  respect,  and  immediately  yield  the  corresponding  hy- 
droxy-compounds.  A  few  aliphatic  amino-compounds  do,  how- 
ever, yield  diazo-derivatives  with  cold  nitrous  acid;  one  of  the 

N\ 
best  known  of  these  compounds  is  ethyl  diazo-acetate,  •  -    >CII- 


ALIPHATIC  TRIAZO-COMPOUNDS  695 

C02Et  (p.  212),  a  yellow  oil,  b.-pt.  141°.  It  differs  from  the 
aromatic  diazonium  salts  in  having  both  nitrogen  atoms  at- 
tached to  carbon,  and  may  be  regarded  as  the  anhydride  of  a 
diazo  hydroxide,  OH  •  N  :  N  •  CBL-  C02Et.  It  is  extremely  re- 
active, and  the  N2  group  is  readily  replaced  by  I2,  HC1,  H^O, 
&c.  With  concentrated  alkalis  it  yields  bis-diazo-  acetic  acid: 


(Curtius,  DurapsJcy,  and  E.  Mutter,  B.  1907). 

The  simplest  aliphatic  diazo-compound  is   cliazo-methane, 
N 
-.,  which  may  be  regarded  as  the  anhydride  of  CH3« 

N:N'OH.  Diazo-methane  is  most  conveniently  prepared  by 
decomposing  nitroso-methyl-urethane,  CH3  •  N(NO)  •  C02Et, 
with  alkali,  the  compound,  CH3»N:N«OK,  being  formed  as 
an  intermediate  product  (Hantzsch  and  Lehmann,  B.  1902.  35, 
897). 

It  is  a  yellow,  odourless  gas  at  atmospheric  temperature, 
and  is  excessively  poisonous.  It  is  characterized  by  its  re- 
activity, and  will  readily  convert  acids  into  methyl  esters, 
alcohols  and  phenols  into  methyl  ethers,  aniline  and  its  homo- 
logues  into  secondary  amines,  and  aldehydes  into  ketones.  It 
is  also  capable  of  uniting  with  unsaturated  compounds,  yielding 
heterocyclic  derivatives,  e.g.: 

CH      N=  CH.NH, 


CH2      N=  CH2.NH 


Cf.  p.  528. 

B.  Triazo-compoimds.—  Forster  (J.  C.  S.  1908,  93,  72,  669, 
1070,  1174,  185$,  1865)  has  obtained  a  number  of  fairly 
simple  aliphatic  triazo-derivatives  containing  the  univalent 

grouping,   ..  ;>N».     Ethyl  triazo-acetate,  N8-CH2.C02C2H5,  ob- 

N/ 

tained  by  the  action  of  sodium  azide,  NaN8,  on  an  alcoholic 
solution  of  ethyl  chloro-acetate,  is  a  colourless  liquid,  b.-pt. 
44°-46°  under  2  mm.  pressure,  and  has  a  sweet  odour  sugges- 
tive of  chloroform.  From  this  ester  triazo-acetic  acid,  m.-pt. 
16°,  and  almost  as  strong  an  acid  as  bromo-acetic,  and  triazo- 
acetamide,  m.-pt.  58°,  have  been  obtained  by  the  ordinary 


696         LI.    ALIPHATIC  1>IAZO-  AND  TRtAZO-COMPOUNDS 

methods.  Triazo-acetone,  acetonyl-azoimide,  N3  •  CH2  •  CO  •  CH3, 
obtained  from  chloro-acetone,  is  a  colourless  liquid,  b.-pt.  54° 
under  2  mm.  pressure.  It  has  the  properties  of  a  ketone,  e.g. 
yields  a  semicarbazone,  m.-pt.  152°,  and  is  instantly  decom- 
posed by  alkalis.  Ethyl  a-triazo-propionate  and  the  isomeric 
/^-compound  have  been  prepared,  and  also  a-triazo-propionic 
add,  CH3»CHN3»C02H,  the  last  of  which  has  been  resolved 
into  optically  active  components.  Ethyl  f$-triazo-propionate  is  so 
readily  decomposed  by  alkalis  that  the  corresponding  acid  and 
amide  have  not  been  prepared.  Allyt-azoimide,  CH2:CH«CH2« 
Nj,  b.-pt.  76-5°;  triazo-ethyl  alcohol,  N3  -  CH2  .  CH2  -  OH,  b.-pt. 
60°/8  mm.;  triazo-acetaldehyde,  an  oil,  together  with  numerous 
esters  derived  from  triazo-ethyl  alcohol,  have  been  prepared. 
Bis-triazo-  compounds  can  be  obtained,  e.g.  bis  -triazo-  ethane, 
N3.CH2.CH2.N3,  and  ethyl  bis-triazo-acetate,  CH(N3)2  •  C02Et, 
but  are  extremely  explosive.  Triazo-malonic  acid  and  ethyl 
triazo-acetoacetate  appear  to  be  incapable  of  existence,  but 
substituted  derivatives,  e.g.  CH3«CO-CN3Me-C02Et,  and  even 
a  bis  -triazo  -compound,  CH3  •  CO  •  C(N3)2  •  (XXEt,  are  known. 
Triazo-ethylene,  N3»CH:CH2,  can  be  obtained  by  eliminating 
hydrogen  iodide  from  triazo-ethyl  iodide.  It  is  a  pale-yellow 
liquid,  b.-pt.  26°,  and  yields  an  oily  dibromide.  Numerous 
aromatic  triazo-compounds  have  also  been  prepared,  mainly 
from  diazonium  salts.  (Cf.  J.  C.  S.  1907,  855,  1350;  1909, 
183;  1910,  126,  254,  1056,  1360,  2570.) 

Staudinger  and  Kupfer  (R  1911,  44,  2197)  and  /.  Thide 
(ibid.  2522)  suggest  that  aliphatic  diazo-compounds  have  an 
open-chain  structure,  e.g.  diazo-methane,  CH2:N|N,  and  like 
the  aromatic  diazonium  salts  contain  a  quinquevalent  nitrogen 
atom.  The  arguments  brought  forward  are:  (1)  The  fact  that 
the  diazo-compounds  can  be  obtained  by  the  oxidation  of 
hydrazones  of  ketones: 

H20. 


(2)  The  azo  group  is  reactive,  yet  in  the  numerous  reactions 
of  the  aliphatic  diazo-compound  such  a  group  does  not  take 
part. 

In  a  similar  manner  hydrazoic  acid  and  its  derivatives  are 
represented  by  open-chain  formulae,  e.g.  HN:N|N.  Such  a 
structure  accounts  for  the  fact  that  by  the  action  of  Grignard 
reagents  azides  yield  diazo-amino-compounds  : 

R-N:N:N  —  >  R-NiN-NHR'. 


INDEX 


a= ana-position,  545. 

ac=alicyclic,  500. 

ar=  aromatic,  500. 

Abietic  acid,  591. 

Absorption  spectra,  647.    . 

Acenaphthene,  504. 

Acet-hydrazide,  185. 

Acetal,  129. 

Acetaldehyde,  128. 

Acetaldehyde-semicarbazone,  136. 

Acetaldoxime,  137. 

Acetals,  125. 

Acetamide,  185. 

Acetamidine,  187. 

Acetamido-chloride,  185. 

Acetanilide,  382. 

Acetates,  151. 

Acetic  acid,  18,  140,  149. 

Acetic  anhydride,  181. 

Acetic  fermentation,  150. 

Acetimido-chloride,  186. 

Acetimido-thio-methyl,  187. 

Aceto-acetanilide,  543. 

Aceto-acetic  acid,  223,  226. 

Aceto-acetic  ester,  226. 

Aceto-acetic  ester  syntheses,  228. 

Aceto-bromamide,  183. 

Aceto-chloroimide,  186. 

Aceto-malpnic  ester,  229. 

Aceto-nitrile,  102. 

Aceto-phenetidine,  415. 

Aceto-phenone,  427. 

Aceto-phenone-acetone,  427. 

Aceto-phenone  oxime,  427. 

Aceto-phenone  phenyl-hydrazone,  427. 

Aceto-succinic  ester,  229. 

Aceto-tartaric  acid,  253. 

Acetone,  136. 

Acetone-dicarboxylic  acid,  261. 

Acetone-dioxalic  acid,  533. 

Acetone  peroxide,  181. 

Acetone-phenyl-hydrazone,  135. 

Acetone-semicarbazone,  136. 

Acetonyl-acetone,  221. 

Acetoxime,  137. 

Acetoluidide,  382. 

Aceturic  acid,  212. 

Acetyl,  147. 

Acetyl-acetone,  221,  544,  655. 

Acetyl-acetone,  constitution  of,  644,  647. 

Acetyl  chloride,  179. 

Acetyl  cyanide,  179. 

Acetyl-diphenylamine,  377, 


Acetyl  glycollic  acid,  209. 

Acetyl  hydride,  128. 

Acetyl  oxide,  180. 

Acetyl  peroxide,  181. 

Acetyl-phenyl-hydrazide,  398, 

Acetyl-urea,  285. 

Acetylaminophenol,  458. 

Acetylene,  52. 

Acetylene-dicarboxylic  acid,  247. 

Acetylene  series,  49. 

Achroo-dextrine,  319. 

Acid  amides,  182. 

Acid  anhydrides,  180. 

Acid  azides,  185. 

Acid  bromides,  180. 

Acid  chlorides,  178,  684. 

Acid  derivatives,  171. 

Acid  esters,  91,  97. 

Acid  green,  484. 

Acid  hydrazides,  185. 

Acid  hydrolysis,  227. 

Acid  salts,  144. 

Acid  violet,  489. 

Acids,  aromatic,  435. 

Acids,  fatty,  140. 

Aconitic  acid,  262. 

Acridine,  548. 

Acridine  yellow,  549. 

Acridinic  acid,  548. 

Acridonium  iodides,  549. 

Acrolei'n,  130. 

Acrolei'n-ammonia,  130. 

Acrolei'n-aniline,  542. 

a-Acrosazone,  312. 

a-Acrose,  312. 

a-Acrosone,  312. 

Acrylic  acid,  161,  164. 

Active  valeric  acid,  154. 

Acyl  derivatives  of  ethyl  aceto-acetate,  229. 

Acyl  oxides,  180. 

Acyl  ureas,  285  et  seq. 

Acyls,  147. 

Additive  compounds  of  aldehydes,  124-126, 

Additive  reactions  of  acetylenes,  50. 

Additive  reactions  of  nitriles,  101. 

Additive  reactions  of  olefines,  44. 

Adenine,  293,  599. 

Adipic  acid,  231. 

^Esculetin,  593. 

^Esculin,  593. 

Alanine,  211,  215,  596. 

Alanylglycyl-glycine,  597. 

Albumins,  594,  599. 


698 


INDEX 


Albumins,  hydrolysis  of,  595. 

Albumins,  oxidation  of,  595. 

Albumoses,  598. 

Alcohol,  75. 

Alcohol,  constitution  of,  17. 

Alcohol  of  crystallization,  79. 

Alcoholic  fermentation,  76,  304,  666. 

Alcohols,  aliphatic,  65. 

Alcohols,  aromatic,  421. 

Alcoholysis,  177. 

Aldehyde,  128. 

Aldehyde-acids,  204,  222. 

Aldehyde-ammonia,  125. 

Aldehyde  "condensations",  126-127. 

Aldehyde-phenyl-hydrazone,  127. 

Aldehyde  resin,  126. 

Aldehydes,  aliphatic,  1 22  et  seq. 

Aldehydes,  aromatic,  423. 

Aldehydes,  the  fuchsine  test  for,  127,  128. 

Aldehydic  acids,  222. 

Aldohexoses,  307. 

Aldoketens,  692. 

Aldol,  131,  220. 

Aldol  "condensations",  131. 

Aldoses,  300. 

Aldoximes  of  the  fatty  series,  127,  137. 

Aliphatic  compounds,  24,  321. 

Alizarin,  509. 

Alizarin  black,  503. 

Alizarin  blue,  510. 

Alizarin  bordeaux,  510. 

Alizarin  cyanine,  510. 

Alizarin  orange,  510. 

Alkaloids,  554  et  seq. 

Alkaloids  from  dead  bodies,  196,  598. 

Alkarsin,  116. 

Alkyl,  22,  366. 

Alkyl  cyanides,  100. 

Alkyl  hydrogen  sulphates,  98. 

Aikyl  hydrosulphides,  88. 

Alkyl-hydroxylamines,  HI. 

Alkyl-malonic  acids,  237. 

Alkyl  nitrites,  94. 

Alkyl  salt,  74,  145. 

Alkyl  sulphates,  98. 

Alkyl  sulphides,  88. 

Alkyl  sulphites,  98. 

Alkylated  ureas,  284. 

Alkylenes,  22,  42,  189. 

Allantoin,  289. 

Allene,  53. 

Allo-cmnamic  acid,  454. 

Allophanic  acid,  285. 

Alloxan,  288. 

Alloxanic  acid,  288, 

Alloxantin,  288. 

Allyl  alcohol,  82. 

Allyl  bromide,  56,  65. 

Allyl  chloride,  56,  65. 

Allyl  ether,  87. 

Allyl  iodide,  56,  65. 

Allyl  "mustard  ou "  =  allyl  Jsothiocyanate, 

An7?'  593> 

A  y  -Py.'-'dine,  538,  557. 

Allyl  sulphide,  91. 
Allyl  thiocyanate,  276. 
Allylene,  53. 
Alphyl,  22,  366. 


Aluminium  amalgam  as  a  reducing  agent 

609. 
Aluminium  chloride,  action  of;  see  Frie~ 

del-Crafts'  synthesis. 
Aluminium  methyl,  120. 
A.malic  acid,  289. 
Amber,  591. 
Amethyst  violet,  §53. 
Amides  of  carbonic  acid,  281. 
Amides  of  malic  acid,  248. 
Amides  of  the  fatty  acids,  182. 
Amidines,  187. 

Amido,  182 ;  see  also  Amino-group, 
Amido  chlorides,  185. 
Amidoximes,  188. 
Amines,  aliphatic,  104,  677. 
Amines,  aromatic,  366. 
Amino-acetic  acid,  211. 
Ammo-acetone,  136. 
Amino-acids,  211. 
Amino-azo-benzene,  397,  400. 
Amino-azo-compounds,  393,  400. 
Amino-azo-naphthalene,  500. 
Amino-benzaldehydes,  426. 
Amino-benzene,  372. 
Amino-benzene-sulphonic  acids,  405. 
Amino-benzoic  acids,  449,  451. 
Amino-benzoyl-formic  acid,  462,  522. 
Amino-caproic  acid  =  Leucine,  216,  596. 
Amino-cinnamic  acids,  456. 
Amino-cinnamic  aldehyde,  543. 
Amino-derivatives,  aromatic,  366. 
Amino-dimethyl-aniline,  378. 
Amino-ethane  acid,  211. 
Amino-ethyl-sulphonic  acid,  197. 
Amino-glutaric-acid,  249,  596. 
Amino-group,  104. 
Amino-guanidine,  297. 
Amino-hexamethylene,  373.  [596- 

a-amino-/3-hydroxy-propionic    acid,     218, 
Amino-hypoxanthine,  293. 
Amino-isobutyl-acetic  acid,  596. 
Amino-ketones,  136. 
Amino-mandelic  acid  lactam,  522,  525. 
Amino-mesitylene,  367. 
Ammo-naphthalenes,  499. 
Amino-naphthols,  502. 
Amino-naphthol-sulphonic  acid,  502. 
Amino-naphthp-tolazine,  551. 
Amino-oxypurine,  293. 
Amino-phenols,  415. 
Amino-phenyl-acetic  acids,  452. 
Amino-phenyl-glyoxylic  acid,  462. 
Amino-propionic  acid;  see  Alanine,  596 
Amino-purme  =  Adem'ne,  293. 
Amino-pyridine,  558. 
Amino-succinic  acid,  249,  596. 
Amino-sugars,  596. 
Amino-thiazole,  530. 
Amino-th jo-lactic  SiC\A  —  Cy stein,  596. 
Amino^thiophene,  519. 
Amino-trimethyl-benzenes,  367, 
Amiiio-triphenyl-methane,  483. 
Ammclide,  277. 
Ammeline,  277. 
Ammonium  acetate,  151. 
Ammonium  cyanate,  273. 
Ammonium  ferri-thiocyanate,  276. 


INDEX 


699 


Ammonium  formate,  148. 

Ammonium  thiocyanate,  275. 

Amphoteric,  451. 

Amygdalin,  267,  423,  592. 

Amyl  acetate,  178. 

Amyl  alcohols,  67,  80,  669. 

Amyl  nitrite,  94. 

Amylase,  671. 

Amylene  glycols,  193. 

Amylenes,  43,  49. 

Amylo-dextrme,  319. 

Amyloid,  317. 

Amylum,  319. 

Analysis,  elementary,  4. 

Analysis,  qualitative,  2. 

Analysis,  quantitative,  4. 

Ana-position,  the,  545. 

Angelic  acid,  161,  165. 

Anhydrides  of  the  fatty  acids,  180. 

Anilic  acids,  382. 

Anilide  of  j^-toluic  acid,  429. 

Anilides,  370,  381. 

Aniline,  367,  372. 

Aniline,  oxidation  of,  617. 

Aniline  blue,  489. 

Aniline  yellow,  401. 

Anilino-quinones,  433. 

Anisaldehyde,  429. 

Anisic  acid,  459. 

Anisidines,  415. 

Anisole,  407,  412. 

Anisyl  alcohol,  429. 

Anomalous  electric  absorption,  655. 

Anthracene,  471,  504. 

Anthracene  brown,  510. 

Anthragallol,  510. 

Anthranil,  452. 

Anthranilic  acid,  452. 

Anthranol,  508. 

Anthrapurpurin,  510. 

Anthraquinone,  477,  508. 

Anthraquinone-sulphonic  acids,  508. 

Anthrarobin,  510. 

Anthrols,  508. 

Anti-albumoses,  598. 

^4w^'-aldoximes,  139,  428. 

Anti-dia.z.0  compounds,  391. 

Anti-febrine,  383. 

Antimony  pentamethyl,  117. 

Antipyrine,  528. 

Aposafranines,  553. 

Arabinose,  219,  306. 

Arabitol,  202. 

Arabonic  acid,  219. 

Arachidic  acid,  140,  157. 

Arbutin,  593. 

Arpfinine,  596. 

Ansto-quimne,  560. 

Aromatic  acids,  435  ei  seq. 

Aromatic  compounds,  321. 

Aromatic  nitriles,  438. 

Aromatic  properties,  328. 

Arsenic  compounds,  115. 

Arsines,  115. 

A  rsonium  compounds,  115. 

Aryl,  366. 

Arylamines,  366. 

Asparagine,  248. 


Aspartic  acid,  249,  596. 

Asphalt,  42. 

Asymmetric  carbon  atoms,  154,  213,  250, 

307,  461.  ^ 

Asymmetric  synthesis,  660. 
Atomic  refractions;  643,  693. 
Atomic  volumes,  640. 
Atropic  acid,  443,  456. 
Atropine,  565. 
Aurichlorides,  107,  370= 
Aurine,  500. 
Australene,  582. 
Auxochromes,  678. 
Azealic  acid,  165. 
Azo-benzene,  394,  396. 
Azo-compounds,  aromatic,  396. 
Azo-dyes,  389,  399. 

Azo-dyes  of  the  naphthalene  series,  502 
Azo-naphthalene,  501. 
Azo-phenines,  434. 
Azo-phenyl-ethyl,  397. 
Azo-phenylene,  551. 
Azoxy-benzene,  394,  395. 
Azoxy-compounds,  394. 

Bacillus  butylicus,  152. 

Baeyer  s  tension  theory,  323. 

Barbituric  acid,  288. 

Beckmann  molecular  transformation,  the. 

137.  139.  429.  479.  687- 
Beer,  78. 

Behemc  acid,  140,  157. 
Benzal  chloride,  358. 
Benzaldehyde,  4231,592. 
Benzaldehyde-<rfanhydrin,  424. 
Benzaldehyde-phenyl-hydrazone,  426. 
Benzaldpximes,  426. 
Benzamide,  446. 
Benzamino-acetic  acid,  447. 
Benzanilide,  446. 
Benz-a«#-aldoxime,  429. 
Benzazide,  447. 
Benzazurine,  474. 
Benzene,  341,  345,  350,  433. 
Benzene,  constitution  of,  332. 
Benzene,  formation,  341,  350. 
Benzene-azo-benzene,  396. 
Benzene-azo-naphthylamine,  502. 
Benzene-carboxylic  acid  =  I}enzoic  acid, 

421,  444. 

Benzene  derivatives,  327. 
Benzene  derivatives,  formation,  341,  344. 
Benzene   derivatives,   isomerism,   332  et 

seq. 

Benzene  derivatives,  occurrence,  341. 
Benzene-diazoic  acid,  388. 
Benzene-diazoimide,  389. 
Benzene-diazonium  perbromide,  389. 
Benzene-dicarboxylic  acids,  464. 
Benzene-disulphonic  acids,  406. 
Benzene  disulphoxide,  413. 
Benzene  formulae,  334  et  seq. 
Benzene  hexabrormde,  354. 
Benzene-hexacarboxylic  acid,  470. 
Benzene  hexachloride,  354. 
Benzene  hydrocarbons,  344  et  seq. 
Benzene  hydrocarbons,   constitution  of 

347- 


700 


INDEX 


Benzene  hydrocarbons,  oxidation  of,  348. 
Benzene  hydrocarbons,  reduction  of,  348. 
Benzene-methylal,  421,  423. 
Benzene-methylol,  421. 
Benzene  nucleus,  328. 
Benzene  of  crystallization,  481. 
Benzene-sulphinic  acid,  405. 
Benzene  sulphonamide,  404. 
Benzene-sulphonic  acidi  403. 
Benzene-sulphonic  chloride,  404. 
Benzene-tetracarboxylic  acids,  470. 
Benzene-tricarboxylic  acids,  470. 
Benzene-trisulphonic  acids,  406. 
Benzhydrazide,  447. 
Benzhydrol,  474,  476. 
Benzidam,  372. 
Benzidine,  395,  472. 
Benzidine-sulphonic  acids,  473. 
Benzil,  479. 
Benzil-oximes,  479. 
Benzilic  acid,  476,  480. 
Benzimido-azoles,  380. 
Benzoic  acid,  443,  444. 
Benzoic  anhydride,  446. 
Benzoic  esters,  445. 
Benzoin,  425,  479. 
Benzoline,  42. 
Benzo-nitrile,  447. 
Benzo-peroxide,  446. 
Benzo-phenone,  428,  474. 
Benzophenone-carboxylic  acid,  476. 
Benzo-purpurine  4  B,  474. 
Benzoquinones,  431,  433. 
Benzo-thiophene,  521. 
Benzo-^-toluidide,  429. 
Benzo-trichloride,  358. 
Benzoyl-acetic  acid,  463. 
Benzoyl-acetone,  427. 
Benzoyl-azimide,  447. 
Benzoyl-benzoic  acids,  476. 
Benzoyl  chloride,  446. 
Benzoyl  cyanide,  462. 
Benzoyl-ecgonine  methyl  ester,  566. 
Benzoyl-formic  acid,  427,  462. 
Benzoyl-glycocoll;  see  Hippuric  acid,  447. 
Benzoyl-nydrazine,  447. 
Benzoyl  peroxide,  446. 
Benzoyl-salicin,  593. 
Benz-syn-aldoxime,  429. 
Benz^-toluidide,  <pg. 
Benzyl-aceto-acetic  ester,  441. 
Benzyl-alcohol,  421,  422. 
Benzyl-benzene ;  see  Diphenyl-methane. 
Benzyl-benzoate,  446. 
Benzyl  chloride,  358. 
Benzyl  cyanide,  452. 
Benzylamine,  367,  383. 
Benzylideneacetone,  428. 
Benzylidene-aceto-phenone,  428. 
Benzylidene-aniline,  371. 
Benzylphenylallylmethyl-ammonium     d- 

camphor-sulphonate,  632. 
Berberine,  563. 
BetaYne,  212. 
Biebrich  scarlet,  402,  503. 
Bilineurine,  196. 
Birotation,  309. 
Bis-azo-dyes,  402. 


Bis-diazo-acetic  acid,  695. 

Bismarck  brown,  401. 

Bismuth  compound,  118. 

Bitter  almond  oil,  423. 

Bitter-almond-oil  green,  484. 

Biuret,  289. 

Blomstrand  formula,  385. 

Blood  colouring-  matter,  600. 

Boiling-point,  26,  635. 

Bonds,    change   in ;    see  Desmotropism, 

227,  650,  651. 
Bone  glue,  579. 
Bone  oil,  518,  535. 
Borneo  camphor,  588. 
Borneol,  588. 
Bornyl  chloride,  584,  589. 
Bornyl  iodide,  584. 
Bornylene,  584. 
Boron  compounds,  118. 
Brassidic  acid,  166. 


Brilliant  black,  503. 
Brilliant  green,  484. 


Brom-anilines,  374. 
Brom-anthraqmnones,  509. 
Bromacetic  acid,  167. 
Bromination,  55,  56,  169,  356. 
Bromine  as  an  oxidizing  agent,  625. 
Bromo-benzene,  3^4. 
Bromo-benzoic  acids,  449. 
Bromo-benzyl  bromide,  505. 
Bromo-camphor,  588. 
Bromo-camphoric  acid,  588. 
Bromo-cinnamic  acids,  455. 
Bromo-ethylene,  65. 
Bromo-naphthalene,  498. 
Bromo-nitro-benzenes,  362. 
Bromo-nitro-camphors,  657,  658. 
Bromo-phenols,  413. 
Bromo-phenyl  hydrazine,  399. 
Bromo-phenyl-mtromethane,  664. 
Bromo-propionic  acids,  167. 
Bromo-propyl-aldehyde,  130. 
Bromo-succmic  acids,  241. 
Bromo-terpane-one,  590. 
Bromoform,  56,  63. 
Brucine,  565. 
Butadiene,  682. 
Butadiine,  53. 
Butane  acid,  152. 
Butane  di-acid,  238. 
Butane-diamine,  195. 
Butane-diol  di-acid,  249. 
Butane-dione,  221. 
Butane-tetrol,  202. 
Butanes,  30,  38. 
Butanol,  73. 
Butanol  di-acid,  247. 
Butanone,  137. 
Butanone  acid,  223. 
Butanone  di-acid,  260. 
2-Butene-i-acid,  164. 
i-Butene;4-acicl,  165. 
Butene  di-acids,  242. 
Butenes^Butylenes,  43,  48. 
Butine  di-acid,  247. 
Butyl-acridine,  548. 
Butyl  alcohols,  67,  80. 
Butyl  bromides,  56,  60. 


INDEX 


701 


Butyl  chlorides,  56,  60. 
Butyl  iodides,  56,  60. 
Butylamines,  no. 
Butylene  glycols,  193. 
«-Butyric  acid,  140,  152. 
Butyric  fermentation,  152. 
Butyro-lactpne,  240. 
Butyro-nitrile,  102. 
Butyryl,  147. 

Cacodyl,  116,  117. 
Cacodyl  chlorides,  116. 
Cacodyl  compounds,  116-117. 
Cacodyl  oxide,  116,  117. 
Cacodylic  acid,  117. 
Cadayerine,  196,  598. 
Cadet s  liquid,  1 16. 
Caffeic  acid,  464. 
Caffeine,  295. 
Cairplin,  546. 
Calcium  carbide,  52. 
Calcium  cyanamide,  278. 
Calcium  glucosate,  302. 
Camphane,  584. 
Camphanic  acid,  588. 
Camphene,  584. 
Camphenilone,  584. 
Campholene  cyanide,  586. 
Campholenic  acid,  586. 
Camphor,  585. 
Camphor,  artificial,  582. 
Camphor,  synthesis  of,  587. 
Camphor-oxime,  585. 
Camphoramic  acid,  588. 
Camphoric  acid,  586,  588. 
Camphoronic  acid,  586. 
Camphylamine,  586. 
Cane  sugar,  314. 
Capillarity  constants,  665. 
Capric  acid,  157. 
Caprilic  acid,  157. 
Caproic  acid,  140,  157. 
Caramel,  315. 
Carbamic  acid,  281,  282. 
Carbamic  chloride,  282. 
Carbamic  compounds,  282. 
Carbamic  esters,  282. 
Carbamide,  281,  282,  595. 
Carbanilide,  383. 
Carbazole,  473. 
Carbinol,  73. 

Carbocinchomeronic  acid,  560, 
Carbocyclic  compounds,  322. 
Carbohydrates,  298  et  seq. 
Carbolic  acid,  411. 
Carbon,  detection  of,  2. 
Carbon,  estimation  of,  4. 
Carbon  monoxide,  683. 
Carbon  monoxide-haemoglobin,  600. 
Carbon  oxychloride,  280. 
Carbon  suboxide,  238. 
Carbon  tetrabromide,  56. 
Carbon  tetrachloride,  <;6,  64,  281. 
Carbonic  acid,  derivatives  of,  279. 
Carbonic  acid,  esters  of,  279,  280. 
Carbonyl  chloride,  280,  683. 
Carbostyril,  453,  456,  £43,  546. 
Carbostyril,  constitution  of,  649. 


Carboxylic  acids,  aromatic,  435. 

Carboxylic  acids,  fatty,  139. 

Carboxylic  group,  140. 

Carbylamines,  102. 

Carbylamines,  constitution  of,  103,  684, 

Carone,  590. 

Caronic  acid,  590. 

Carvacrol,  408,  417,  573. 

Carvene,  568. 

Carvenone,  590. 

Carvestrene,  576. 

Carvo-menthol,  579. 

Carvone,  573,  577,  579. 

Carvotanacetone,  577. 

Carvoxime,  575,  576. 

Casein,  599. 

Caseinogen,  599. 

Catalytic  dehydration,  674. 

Catalytic  oxidation,  674. 

Catalytic  reduction,  610. 

Catechol,  408,  4x7. 

Cellulose,  317. 

Centric  formula  of  benzene,  335. 

Cerotene,  43,  49. 

Cerotic  acid,  140,  157,  158. 

Ceryl  alcohol,  81. 

Ceryl  cerotate,  178. 

Cetene,  43. 

Cetyl  alcohol,  81. 

Cetvl  palmitate,  178. 

Chain  isomerism,  87. 

Chains,  closed,  20,  24,  321. 

Chains,  open,  20,  321. 

Chalcone,  428. 

Chelidonic  acid,  533. 

Chemical  retardation,  175,  449. 

Chlor-acetanilide,  373. 

Chlor-acetic  acids,  167,  170,  210. 

Chloracetyl  chloride,  210. 

Chloral,  129. 

Chloral  alcoholate,  130. 

Chloral  hydrate,  130. 

Chloranil,  432. 

Chloranilic  acid,  433. 

Chlorhydrins,  193,  199. 

Chlorination,  56,  356. 

Chlorine  as  an  oxidizing  agent,  625. 

Chloro-aceto-acetic  ester,  230. 

Chloro-amylamine,  535. 

Chloro-aniline,  373. 

Chloro-benzene,  336. 

Chloro-benzoic  acid,  448,  449. 

Chloro-bromo-benzenes,  358. 

Chloro-butene  acid,  171. 

Chloro-camphor,  568- 

Chloro-carbonic  acid,  280. 

Chloro-carbonic  ester,  280. 

Chloro-crotonic  acids,  171. 

Chloro-ethane  acid,  170. 

Chloro-formic  acid,  170,  280. 

Chloro-malonic  ester,  238. 

Chloro-methane-oxy-methanol,  128, 

Chloro-methanol,  128. 

Chloro-methyl  alcohol,  128. 

Chloro-naphthalenes,  498. 

Chloro-nitro-benzenes,  362, 

Chloro-phenols,  413. 

Chloro-picrin,  97. 


702 


INDEX 


Chloro-propane-dfols,  200. 

Chloro-propene,  65. 

Chloro-propionic  acids,  167,  171. 

Chloro-propylene,  65. 

Chloro-pyridine,  536. 

Chloroform,  56,  63. 

Cholestrophane,  287. 

Choline,  196. 

Chondrin,  599. 

Chromic     anhydride    as     an    oxidizing 

agent,  620. 
Chromogene,  399. 
Chromone,  541. 
Chromophores,  399. 

Chromo-proteins,  600.  [620. 

Chromyl  chloride  as  an  oxidizing  agent, 
Chrysamine,  473. 
Chrysaniline,  548. 
Chrysene,  512. 
Chrysin,  541. 
Chrysoidine,  401. 
Chrysoidines,  400. 
Cinchene,  560. 
Cinchomeronio  acid,  540. 
Cinchona  bases,  558. 
Cinchonidine,  560. 
Cinchonine,  560. 
Cinchoninic  acid,  560. 
Cineol,  581. 
Cinnamene,  353. 
Cinnamenyl  radical,  456. 
Cinnamic  acids,  443,  454. 
Cinnamic  alcohol,  422. 
Cinnamic  aldehyde,  426. 
Cinnamo-carboxylic  acid,  502. 
Cinnamon,  oil  of,  426. 
Cinnamyl  radical,  456. 
Cinnamylideneacetic  acid,  682. 
Cinnamylidenemalonic  acid,  682. 
"Cis-"  form,  246,  326. 
Citral,  570. 
Citrazinic  acid,  263. 
Citrene,  368. 
Citric  acid,  262. 
Citric  esters,  262. 
Citron,  oil  of,  568. 
Citronellal,  569. 
Classen  reaction,  225. 
Classification  of  organic  compounds,  23, 

321. 

Closed  chains  (rings),  20,  24,  321  et  seq. 
Clupeine,  596. 
Cocaine,  566. 
Codeine,  564. 
Co-enzymes,  667,  668. 
Collidines,  539. 
Collodion,  317. 
Colophonium,  581,  591. 
Combustion  of  hydrocarbons,  36. 
Complex  cyanides,  269. 
Conchinine,  £60. 
"  Condensation  ",  126. 
Condensed  benzene  nuclei,  471  et  seq. 
Configuration,  spatial,  155. 
"Congo "(dye),  473. 
Coniferin,  430,  493. 
Comferyl  alcohol,  429,  430,  493. 
Conune,  538,  557. 


Conjugate  double  bonds,  681,  693. 
Constitution  of  fructose,  311. 
Constitution  of  glucose,  310. 
Constitution  of  organic  compounds,  16. 
Constitutional  formula,  17. 
Continuous  formation  of  ether,  84. 
Conyrine,  538. 
Copellidine,  540. 

Copper  powder  and  hydrogen   as  a  re- 
ducing agent,  611. 
Copper-zinc  couple,  35. 
Coriandrol,  572. 
Corydaline,  563. 
Cotarnine,  562. 
Coumaric  acids,  443,  463. 
Coumarilic  acid,  520. 
Coumarin,  463. 
Coumarinic  acid,  463. 
Coumarone,  520. 
Coumarone  dibromide,  520. 
Coumarone  picrate,  520. 
Creatine,  298. 
Creatinine,  298. 
Cremor  tartari,  253. 
Creosol,  419. 
Cresols,  408,  416. 
Crotonic  acids,  161,  164. 
Crotonic  aldehyde,  130. 
Cryoscopic  method,  10. 
Crystal  violet,  488. 
Crystalline,  372. 
Cumene,  345,  352. 
Cupric  ferrocyanide,  269. 
Cyamelide,  271. 
Cyanamide,  277. 
Cyanates,  271. 
Cyanhydrins,  126,  135,  206. 
Cyanic  acid,  273. 
Cyanic  ester,  273. 
Cyanides,  metallic,  269  et  seq. 
Cyanines,  546. 
Cyanmethine,  102. 
Cyano-acetic  acid,  167,  171. 
Cyano-carbonic  ester,  237. 
Cyano-fatty  acids,  170. 
Cyano-nitroacetamide,  690. 
Cyano-propipnic  acids,  171. 
Cyano-pyridine,  537-538. 
Cyanogen,  237,  266. 
Cyanogen  bromide,  272. 
Cyanogen  chloride,  272. 
Cyanogen  compounds,  263  et  seq. 
Cyanogen  iodide,  272. 
Cyanogenetic  glucosides,  592. 
Cyanol,  372. 
Cyanuramide,  277. 
Cyanuric  acid,  274. 
Cyanuric  chloride,  271. 
Cyanuric  esters,  273. 
Cyclic  ammonium  salts,  197,  212. 
Cyclic  compounds,  24,  321. 
Cyclic  ureides,  286. 
Cyclo-butane,  322. 
Cyclo-butane-dione,  692. 
Cyclo-hexane-diol,  419. 
Cyclo-hexane-dione,  432. 
Cyclo-propane,  322. 
Cymene,  345,  352,  572. 


INDEX 


703 


Cystein,  596. 
Cystin,  596. 

d=  dextro-rotatory,  154,  249. 

Deca-tetrine  di-acid,  247. 

Decane,  30. 

Decyl  alcohol,  67. 

Decylene,  43. 

Dehydration,  catalytic,  674-677. 

Deka-hydronaphthalene,  497. 

Deoxy-benzoi'n,  479. 

Dephlegmators,  78. 

Desmotropism,  227,  650,  651. 

Determination  of  configuration   of  hex- 

oses,  308. 
Determination  of  configuration  of  olefine 

compounds,  246. 
Determination  of  configuration  of  oximes, 

139,  429,479. 
Dextrmes,  319. 
Dextro-limonene,  575. 
Dextro-tartaric  acid,  252  et  seg. 
Dextrose,  309. 
Dhurrin,  592. 
Diacetamide,  185. 
Diacetanilide,  383. 
Diaceto-acetic  ester,  229. 
Diacetoglutaric  acid,  261. 
Diaceto-succinic  acid,  261. 
Diaceto-succinic  ester,  229. 
Diacetyl,  205,  221. 
Diacetyl-dihydrazone,  222. 
Diacetyl-osazone,  222. 
Diacetylene,  33. 

Diacetylene-dicarboxylic  acid,  247. 
Diagonal  formula  of  benzene,  336. 
Di-aldehydes,  97,  204,  221. 
Di-allyl,  53. 
Dialuric  acid,  288. 
Diamide ;  see  Hydrazine. 
Diamines,  189,  194,  195. 
Diamines,  aromatic,  380. 
Diamino-acetic  acid,  596. 
Diamino-azo-benzene,  401. 
Diamino-azo-benzene  hydrochloride,  401. 
Diamino-caproic  acid,  219,  596. 
Diamino-dimethyl-acridine,  548. 
Diamino-diphenyl,  472,  473. 
Diamino-diphenyl-methane,  476. 
Diamino-phenazine,  552. 
Diamino-phenyl-acridme,  548. 
Diamino-stilbene,  478. 
Diamino-triphenyl-methane,  483. 
Diamino-valeric  acid  =  Ornithine,  219,596. 
Dianilino-quinone-dianile,  434. 
Di-anisidine,  474. 
Diastase,  77,  671. 
Diazines,  549. 
Diazo-amino-benzene,  394. 
Diazo-amino-compounds,  392  et  seg. 
Diazo-amino-naphthalene,  500. 
Diazo-benzene-sulphonic  acid,  406. 
Diazo-benzoic  acids,  451. 
Diazo-compounds,  384,  390. 
Diazo-compounds,  fatty,  212,  694. 
Diazo-compounds,  isomerism  of,  391. 
Diazo-guanidine,  298. 
Diazo-methane,  695. 


Djazonium  salts,  384. 
Diazotizing,  386. 
Dibasic  acids,  saturated,  231. 
Dibenzyl,  471,  477. 
Dibromo-acetic  acid,  167. 
Dibromo-benzeries,  357. 
Dibromo-propionic  acids,  167. 
Dibromo-propyl  aldehyde,  130. 
Dibromo-succinic  acids,  241. 
Dicetyl  ether,  87. 

Dichlor-hydrins ;  see  Chlorhydrins. 
Dichloro-acetic  acid,  167,  170. 
Dichloro-aceto-acetic  ester,  230. 
Dichloro-butyro-lactone,  240. 
Dichloro-isoquinoline,  547. 
Dichloro-maleic  acid,  343. 
Dichloro-propane-ols,  200. 
Dichromates  as  oxidizing  agents,  620 
Diethyl ;  see  Normal  butane,  38. 
Diethyl-aniline,  367,  379. 
Diethyl-butyro-lactone,  240. 
Diethyl-cyanamide,  278. 
Diethyl-disulphide,  89. 
Diethyl  ether,  85. 
Diethyl-hydrazine,  112. 
Diethyl  ketone,  133. 
Diethyl  nitrosamme,  112. 
Diethyl  peroxide,  181. 
Diethyl-semi-carbazide,  ii2» 
Diethyl  sulphide,  88. 
Diethyl  sulphone,  89. 
Diethyl  sulphoxide,  89. 
Diethyl-thio-urea,  296. 
Diethyl-urea,  112,  285. 
Diethylamine,  no,  in. 
Diethylamino-phenol,  415. 
Dieth}dene-diamine,  195. 
DigitaleYn,  593. 
Digitalin,  593. 
Digitomn,  593. 
Digitoxin,  593. 
Di-glycollic  acid,  210. 
Di-glycollic  anhydride,  210. 
Di-hydrazones,  221,  301. 
Di-hydric  alcohols,  188. 
Di-hydric  phenols,  417. 
Dihydro-anthracene,  507. 
Dihydro-benzenes,  349. 
Dihydro-benzoic  acids,  445. 
Dihydro-carvone  hydrobromide,  590. 
Dihydro-cinnamylidene-acetic  acid,  682= 
Dihydro-collidine-dicarboxylic  ester,  535 
Dihydro-coumarone,  520. 
Dihydro-cymene,  578. 
Dihydro-methyl-pyridine,  537. 
Dihydro-phenazine,  551. 
Dihydro-phthalic  acids,  466. 
Dihydro-pyridines,  540. 
Dihydro-quinoline,  546. 
Dihydro-terephthalic  acids,  467-468. 
Dihydroxy-acetone,  669. 
Dihydroxy-anthranol,  510. 
Dihydroxy-anthraquinones,  509. 
Dihydroxy-benzenes,  417. 
Dihydroxy  benzoic  acids,  459. 
Dihydroxy-benzo-phenone,  486,  492. 
Dihydroxy-camphoric  acid,  587. 
Dihydroxy-cinnamic  acids,  464, 


704 


Dihydroxy-coumarine,  593. 
Dihydroxy-dihydro-terephthalic  acid,  469. 
Dihydroxy-diphenyls,  473. 
Dihydroxy-flavone,  541. 
Dihydroxy-hexamethylene,  419. 
Dihydroxy-naphthaquinones,  503. 
Dihydroxy-purine,  292. 
Dihydroxy-stilbene,  682. 
Dihydroxy-tartaric  acid,  261,  343. 
Dihydroxy-terephthalic  acid,  469. 
Dihydroxy-toluene,  419. 
Di-iodo-phenol-sulphonic  acid,  416. 
Diketo-butane,  221. 
Diketo-camphoric  ester,  587. 
Diketo-hexamethylene,  419,  432,  469. 
Diketo-hexane,  221. 
Diketones,  221,  224. 
Di-lactic  acid,  215. 
Dill,  oil  of,  575. 

Dimethoxy-benzidine,  474.  [$6i. 

Dimethoxybenzyl-dimethoxyisoquinolme, 
Dimethyl-acetic  acid,  153. 
Dimethyl-aceto-acetic  ester,  228. 
Dimethyl-acrylic  acid,  680. 
Dimethyl-allene,  669. 
Dimethyl-allpxan,  288. 
Dimethylamine,  no. 
Dimethyl-amino-azo-benzene,  400. 
Dimethyl -amino-azo-benzene-sulphonic 

acid,  401. 

Dimethyl-aniline,  367,  378. 
Dimethyl-arsine  compounds,  115,  117. 
Dimethyl-benzenes ;  _see  Xylene,  351. 
Dimethyl-benzoic  acids,  453. 
Dimethyl-butane-diol,  193. 
2-Dimethyl-3-butanone,  137.  [583. 

Dimethyl-cyclobutane-dicarboxylic  acid, 
Dimethyl-cyclohexenone,  342. 
Dimethyl-diamino-tolu-phenazine,  551. 
Dimethyl  ether,  86. 
Dimethyl-furane,  517. 
Dimethyl-keten,  692. 
Dimethyl-ketol,  205. 
Dimethyl  ketone,  136. 
Dimethyl-naphthylamines,  500. 
Dimethyl-nitrosamine,  108. 
Dimethyl-oxamic  ester,  106. 
Dimethyl-oxamide,  106,  236. 
Dimethyl-parabanic  acid,  287. 
Dimethyl-phenylamine  oxide,  378. 
Dimethyl-phosphinic  acid,  114. 
Dimethyl-piperidonium  iodide,  540. 
Dimethyl-pyrazine,  550. 
Dimethyl-pyridines,  539. 
Dimethyl-pyrone,  531. 
Dimethyl-pyrrole,  518. 
Dimethyl-quinoline,  544. 
s-Dimethyl-succinic  acids,  241. 
Dimethyl-thiophene,  516. 
Dimethyl  -  trimethylene  -  dicarboxylic  acid 

=  Caronic  acid,  590. 
Dimethyl-uric  acids,  292. 
Dimethyl-xanthine,  293. 
Dinaphthols,  502. 
Dinaphthyls,  ^04. 
Dinicotinic  acid,  540. 
Dinitro-benzenes,  360,  361. 
Dinitro-diphenyl,  472. 


Dinitro-ethane,  97. 
Dinitro-naphthalenes,  499. 
Dinitro-phenols,  414. 
Dinitro-toluenes,  360,  362. 
Dionine,  564. 
Dioximes,  479. 
Dioxindole,  522,  525. 
Dipalmitin,  201. 
Dipentene,  374. 

Dipentene  dihydrochloride,  575,  578. 
Dipentene  tetrabromide,  578. 
Diphenic  acid,  474. 
Diphenyl,  471. 
Diphenyl-acetic  acid,  476. 
Diphenyl-acetylene ;  see  Tolane,  478, 
Diphenyl-benzene,  474. 
Diphenyl-bromo-methane,  476. 
Diphenyl-butadiene,  628. 
Diphenyl-butyro-lactone,  240. 
Diphenyl-carbinol,  476. 
Diphenyl-carbo-di-imide,  279. 
Diphenyl-carboxylic  acids,  473,  477. 
Diphenyl-ethane,  474,  476. 
Diphenyl-ethylene,  478. 
Diphenyl-glycol,  478. 
Diphenyl-glycollic  acid,  476. 
Diphenyl  group,  470. 
s-DiphenyT-hydrazme,  396. 
unsym.-Diphenyl-hydrazine,  398. 
Diphenyl-hydrazones,  221,  301. 
Diphenyl-keten,  692. 
Diphenyl  ketone,  428. 
Diphenyl-methane,  471,  474,  476. 
Diphenyl-nitrosamine,  377. 
Diphenyl-oxide,  412. 
Diphenyl-quinp-methane,  692. 
Diphenyl-succino-nitrile,  268. 
Diphenyl-thio-urea,  383. 
Diphenyl-urea ;  see  Thiocarbanilide, 
Diphenylamine,  377. 
Diphenylene  ketone,  477. 
Diphenylene-methane,  477. 
Diphenylene-methane  oxide,  548. 
Diphenylene  oxide,  473. 
Diphenyline,  473. 
Dipicohnic  acid,  540. 
Dippel's  oil,  535. 
Dipropareyl,  53. 
Dipropyl  ketone,  133. 
Dipyndine,  537. 
Dipyridyl,  537. 
Disaccharoses,  299. 
Dissociation  constants  of  acids,  160,  167, 

447,  664. 

Distillation*  fractional,  27. 
Distillation,  steam,  27. 
Disulphides,  89. 
Disulphoxides,  89. 
Dithio-carbamic  acid,  296. 
Dithio-carbonic  acid,  295. 
Diurea,  284. 
Divalent  carbon,  683. 
Dodecane,  30. 
Dodecyl  alcohol,  67. 
Dodecylene,  43. 
Double  bond,  44,  643. 
Dulcitol,  203,  307. 
Durene,  345,  352. 


IND  ^ 


705 


Dye,  400. 
Dyeing,  399. 
Dynamic  isomensm,  657. 
Dynamite,  201. 

Earth-pitch,  42. 
Ebulliscopic  method,  n. 
Ecg-onine,  566. 
Egg  albumin,  599. 
Eicosane,  30. 
Eicosylene,  43. 
Eikonogen,  502. 
ElaVdic  acid,  165. 
Elastin,  599. 

Electrical  conductivity,  161,  663. 
Electrolytic  oxidation,  626. 
Electrolytic  reduction,  614. 
Elementary  analysis,  4. 
Empirical  Formulae,  7. 
Emulsin,  267,  423,  592,  672. 
Enzymes,  76,  77,  671. 
Eosin,  493. 

Eosin  group,  the,  491. 
Epichlorhydrin,  200. 
Erigeron,  oil  of,  575. 
Erucic  acid,  161,  166. 
Erythrin,  202. 
Erythritol,  202. 
Erythro-dextrine,  319. 
Erythrose,  306. 
Erythrosin,  493. 
Ester  alcohols,  189. 
Esterification,  172,  449,  677.  ^ 
Esters,  74,  91,  172,  445. 
Etard  reaction,  the,  424,  620. 
Ethanal,  128. 
Ethanal  acid,  222. 
Ethane,  30,  37. 
Ethane  acid,  149. 
Ethane-amide,  185. 
Ethane-amidine,  187. 
Ethane  di-acid,  234. 
Ethane-dial,  221. 
s-Ethane-dicarboxylic  acid,  238. 
Ethane-nitrile,  102. 
Ethane-oxy-ethane,  85. 
Ethane-tetra-carboxylic  ester  (symmetr.), 
Ethane-thio!,  88.  [495. 

Ethane-thiolic  acid,  181. 
Ethane-thion-amide,  186. 
Ethanol,  75. 
Ethanolic  acid,  209. 
Ethanoyl  chloride,  179. 
Ethene,  48. 

Ethenyl-amidoxime,  188. 
Ethenyl-diphenyl-amidine,  187. 
Ether,  85.  _ 
Ethereal  oils,  567. 
Ethers,  83. 
Ethers,  mixed,  84. 
Ethers,  phenolic,  407. 
Ethers,  simple,(  84. 
Ethidene  chloride,  62. 
Ethine,  52. 
Ethoxy-group,  177. 
Ethyl  acetate,  178. 
Ethyl-acetchloroamide,  186. 
Ethyl-acetchloroimide,  186. 
(B480) 


Ethyl-acetic  acid,  152. 

Ethyl  aceto-acetate,  226. 

Ethyl  aceto-acetate,  constitution  of,  227,, 

643,  646,  650,  653,  654. 
Ethyl  adipate,  232. 
Ethyl  alcohol,  67,  75. 
Ethyl  benzene,  345,  351. 
Ethyl  benzoate,  445. 
Ethyl-benzoic  acids,  443. 
Ethyl  benzoyl-acetate,  647,  655. 
Ethyl  bromide,  56. 
Ethyl  butyrate,  178. 
Ethyl  carbamate,  282. 
Ethyl  carbonate,  279. 
Ethyl-cetyl-ether,  87. 
Ethyl  chloride,  56. 
Ethyl  chloro-carbonate,  280. 
Ethyl  chloro-formate,  280. 
Ethyl  collidine-dicarboxylate,  536. 
Ethyl  cyanamide,  278. 
Ethyl  cya.r\\Ae.  =  P-ropior>iiti'ile,  102. 
Ethyl  cyanurate,  274. 
Ethyl  diazoacetate,  212,  694. 
Ethyl  dibenzoyl-succinates,  649. 
Ethyl  dichloro-amine,  in. 
Ethyl  dihydrocollidine-dicarboxylate,  230. 
Ethyl  diketo-apocamphorate,  587. 
Ethyl  diketo-camphorate,  587. 
Ethyl  dimethyl-aceto- acetate,  228. 
Ethyl  dimethylacrylate,  590. 
Ethyl  dimethyl-oxamate,  237. 
Ethyl    dimethyl  -  propanetricarboxylate, 
Ethyl  disulphide,  89.  [590. 

Ethyl  disulphoxide,  89. 
Ethyl  ethanetricarboxylate,  239. 
Ethyl  ether,  85. 
Ethyl  ethyl-aceto-acetate,  228. 
Ethyl  ethyl-keten-carboxylate,  693. 
Ethyl  ethylsulphonate,  100. 
Ethyl  fluoride,  60. 
Ethyl  formate,  178. 
Ethyl  glycollate,  209. 
Ethyl-glycollic  acid,  209,  210. 
Ethyl  green,  489. 
Ethyl  hydrazine,  112. 
Ethyl  hydrogen  carbonate,  280. 
Ethyl  hydrogen  peroxide,  181. 
Ethyl  hydrogen  sulphate,  98. 
Ethyl  hydrogen  sulphite,  99. 
Ethyl  hydrosulphide,  88. 
Ethyl  ^-hydroxy-trimethylglutarate,  586, 
Ethyl-indoxyl,  523. 
Ethyl  indoxylate,  523. 
Ethyl  iodide,  56. 
Ethyl  isocyanate,  273. 
Ethyl  isocyanide,  103. 
Ethyl  isocyanurate,  275. 
Ethyl  isothiocyanate,  277. 
Ethyl  lactate,  215. 
Ethyl  lactate,  molecular  magnetic  rota 

tion  of,  646. 
Ethyl-lactic  acid,  215. 
Ethyl  malonate,  237. 
Ethyl  mercaptan,  88. 
Ethyl-methyl-acetic  acid,  154. 
Ethyl  methyl-aceto-acetate,  aa6. 
Ethyl  nitrate,  93. 
Ethyl  nitrite,  94. 


706 


INDEX 


Ethyl-nitrogen  chloride,  in. 

Ethyl-nitrolic  acid,  96. 

Ethyl  orthocarbonate,  281. 

Ethyl  orthoformate,  142,  197. 

Ethyl  oxalacetate,  224,  260,  655. 

Ethyl  oxalate,  234,  236. 

Ethyl  oxalate,  reactions  of,  with  amines, 

Ethyl  oxalic  acid,  234,  236.  [106. 

Ethyl-oxalyl  chloride,  236. 

Ethyl  oxamate,  236. 

Ethyl  oxamic  chloride,  237. 

Ethyl  phenylaminpcrotpnate,  543. 

Ethyl    phloroglucinoldicarboxylate,    343, 


419,  441 
th 


,        . 
Ethyl  propanetetracarboxylate,  240. 


Ethyl  propylbenzylphenylsilicane,  630. 
Ethyl     propyldibenzylsilicane     monosul- 

phonic  acid,  630. 
Ethyl-pyridines,  538. 
Ethyl  pyruvate,  654. 
Ethyl  succinylosuccinate,  241,  342,  578. 
Ethyl  sulphate,  98. 
Ethyl  sulphide,  88. 
Ethyl-sulphinic  acid,  100. 
Ethyl  sulphite,  99. 
Ethyl  sulphone,  89,  90. 
Ethyl-sulphonic  acid,  89,  90,  99. 
Ethyl-sulphonic  chloride,  100. 
Ethyl  sulphoxide,  89. 
Ethyl  tartrates,  253. 
Ethyl    tetrahydronaphthalene  -  tetra-car  - 

boxylate,  495. 
Ethyl  thiocyanate,  276. 
Ethyl  triazoacetate,  695. 
Ethyl     trimethyldihydropyridine  -  dicar  - 

boxylate,  535. 
Ethyl-urea,  285. 
Ethyl  violets,  489. 
Ethylamine,  no,  in. 
Ethylamine  ethyldithiocarbamate,  296. 
Ethylaniline,  367. 
Ethylene,  43,  48. 
Ethylene  bromide,  56,  62. 
Ethylene-carbpxylic  acid,  164. 
Ethylene  chloride,  56,  62. 


•     .-  195- 

Ethylene-dicarboxylic  acids,  246. 
Ethylene-glycol,  192. 
Ethylene-lactic  acid,  216. 
Ethylene  oxide,  191,  194. 
Ethylene-succinic  acid,  238. 
Ethylidene-aniline,  543. 
Ethylidene  bromide,  56,  62. 
Ethylidene  chloride,  56,  62. 
Ethylidene  cyanhydrin,  126,  194. 
Ethylidene-glycol,  192. 
Ethylidene-lactic  acids,  213  et  seq. 
Ethylidene-succinic  acid,  241. 
E  thylol  -  trimethyl  -  ammonium  hyd  roxide, 
Eucaine,  567.  [196. 

Eucalyptus  oil,  581. 
Euquinine,  560. 
Eurhodine,  551. 
Eurhodol,  552. 
Euxanthone,  549. 
Even  numbers,  law  of,  21. 


Exhaustive    methylation,    540,    556,    564, 
Extraction  with  ether,  28.  [569, 

Fast  red,  503. 

Fast  yellow,  502. 

Fats,  158,  198,  201. 

Fatty  acid  series,  140. 

Fatty  compounds,  24.1 

Fatty  compounds  from  benzene  deriva- 
tives, 343. 

Fehlings  solution,  253. 

Fermentation  amyl-alcohol,  80. 

Fermentation  lactic  acid,  214. 

Fermentations,  76,  214,  666. 

Ferments,  76. 

Ferments,  unorganized;  see  Enzymes, 
76,  423,  671. 

Ferric   chloride   as  an   oxidizing    agent, 

Ferropotassic  oxalate,  236.  [626. 

Ferulic  acid,  464. 

Fibrin,  599. 

Fibrinogen,  599. 

Fire-<lamp,  34. 

Fittigs  synthesis,  344. 

Flavone,  541. 

Flavo-purpurin,  510. 

Fluorane,  492. 

Fluoranthene,  512. 

Fluorene,  477. 

Fluorenyl  alcohol,  477. 

Fluorescein,  493. 

Formaldehyde,  128. 

Formalin,  128. 

Formamide,  185. 

Formanilide,  382. 

Formhydroxamic  acid,  689. 

Formic  acid,  140,  147,  677. 

Formo-rhodamine,  549. 

Formose,  128,  312. 

Formula,  calculation  of  the  empirical,  7. 

Formulas,  constitutional,  17  et  seq. 

Formyl  chloride,  684. 

Formyl  chloride  oxime,  689. 

Formyl-diphenylamine,  548. 

Fractional  distillation,  27. 

Freezing  temperature  of  solutions,  to. 

Friedel-Crafts    synthesis,   346,  427,  475, 

Fructose,  311.  [481. 

Fruit  sugar,  311. 

Fuchsine,  484,  485. 

Fuchsine-sulphurous  acid,  488. 

Fucose,  307. 

Fulminic  acid,  687. 

Fulminuric  acid,  690. 

Fumaric  acid,  242. 

Furaldehyde,  306,  517,  596. 

Furalmalonic  acid,  518. 

Furane  or  Furfurane,  322,  514,  517. 

Furane-carboxylic  acid,  518. 

Furo'in,  518. 

Furol,  517. 

Furylacrylic  acid,  518. 

Fusel  oil,  76,  669. 

Galactonic  acid,  307. 
Galactoses,  307,  310. 
Galipot  resin,  591. 
Gallein,  493. 


INDEX 


707 


Gallic  acid,  460. 
Gallo-tannic  acid,  460. 
Gelatin,  599. 
Geranial,  570. 
Geranic  acid,  570. 
Geraniol,  570,  571. 
Gladstone-  Tribe  couple,  33. 
Gliadins,  599. 
Lrlobulms,  599. 
Gluconic  acid,  219,  307. 
Gluco-proteins,  600. 
Glucose-phenylhydrazone,  309. 
Glucose  phosphate,  668. 
Glucosamines,  596. 
Glucoses,  307,  309. 
Glucosides,  303,  592,  672. 
Glucosone,  309^"^-'-" 
Glutamic  acid,  249,  596,  670= 
Glutamine,  249. 
Glutaric  acid,  231,  240,  241. 
Glutaric  anhydride,  530. 
Gluteins,  599. 
Glyceric  acid,  218. 
Glyceric  aldehyde,  220. 
Glycerides,  141,  201. 
Glycerine,  198. 
Glycerine  nitrates,  200. 
Glycerol,  76,  198,  669. 
Glycerol  chlorhydrins,  200. 
Glycerose,  306. 
Glyceryl-chloride,  64. 
Glyceryl-phosphoric  acid,  199. 
Glyceryl-sulphuric  acid,  199. 
Glyceryl-trinitrate,  199,  201. 
Glyceryl-tripalmitate,  158,  201. 
Glycide  alcohol,  199,  200. 
Glycide  compounds,  200. 
Glycine,  211. 
Glycocoll,  210,  211,  596. 
Glycocoll,  salts  of,  211. 
Glycocyamidine,  298. 
Glycocyamine,  298. 
Glycogen,  319. 
Glycol,  192! 
Glycol,  ethers  of,  193. 
Glycol  bromhydrins,  191. 
Glycol  chlorhydrins,  191,  193. 
Glycol  iodhydrin,  191. 
Glycolide,  210. 
Glycollamide,  209,  210. 
Glycollic  acetates,  189. 
Glycollic  acid,  204,  205,  209. 
Glycollic  aldehyde,  204,  220. 
Glycollic  anhydride,  210. 
Glycollic  di-nitrate,  193. 
Glycollyl  chloride,  209,  210. 
Glycols,  188. 
Glycoluric  acid,  285. 
Glycolyl-urea,  285. 
Glycuronic  acid,  222. 
Glycylglycine,  597. 
Glyoxal,  204,  221. 
Glyoxalic  acid,  204,  222. 
Glyoxalin,  530. 
Glyoxylic  acid,  222. 
Grape  sugar,  309. 

Grignarcts  reagents,  72,  120  et  seq.,  126, 
»43»  3S6.  422.  424.  428-  44°.  481. 


Guaiacol,  418. 

Guanidine,  278,  281,  297. 

Guanine,  293,  599. 

Guanino-amin^'ajeric  acid,  596. 

Guldberg  and  nonage's  law,  160,  173. 

Gulonic  acid,  307. 

Guloses,  307. 

Gum  benzoin,  444. 

Gums,  319. 

Gun  cotton,  317. 

Guye's  hypothesis,  656. 

Haematin,  600. 

Haemin,  600. 

Haemoglobin,  6op. 

Halogen  derivatives  of  the  aromatic  series, 

Halogen  derivatives  of  the  fatty  series, 

Halogens,  detection  of,  3.  [54. 

Halogens,  estimation  of,  6. 

Haloid  fatty  acids,  167. 

Hatchett's  brown,  269. 

Heat  of  combustion,  665. 

Helianthin,  401. 

Heliotrope,  429. 

Hemi-albumoses,  598. 

Hemi-mellithene,  345. 

Hemi-mellitic  acid,  470. 

Hemiterpenes,  567. 

Heiieicosane,  30. 

Hentria-contane,  30. 

Heptane,  30. 

Heptoic  acid,  140. 

Heptoses,  300. 

Heptyl  alcohol,  67. 

Heptylene,  43. 

Heptylic  aldehyde,  129. 

Heroin,  564. 

Hesperidene,  568. 

Hesperidin,  593. 

Heterocyclic  compounds,  24,  322,  513. 

Hexabromo-benzene,  343,  357. 

Hexachloro-benzene,  343,  357. 

Hexachloro-ethane,  64. 

Hexa-contane,  30. 

Hexa-decane,  30. 

Hexa-decylene,  43. 

Hexa-diene,  53. 

Hexa-diine,  53. 

Hexahydric  alcohols,  201,  203. 

Hexahydro-benzene,  349. 

Hexahydro-benzoic  acid,  445. 

Hexahydro-isophthalic  acid,  342,  469. 

Hexahydro-naphthalene,  497. 

Hexahydro-phenol,  412. 

Hexahydro-phthaJic  acid,  466. 

Hexahydro-pyridine  =  Pfyeridine,  534. 

Hexahydro-terephthalic  acid,  468. 

Hexahydro  -  tetrahydroxy  -  benzoic    acid, 

Hexahydro-xylenes,  351.  [461, 

Hexahydroxy-benzene,  420. 

Hexa-methyl-benzene,  353. 

Hexamethyl-para-rosanihne,  488. 

Hexa-methylene  =  Cyclo-hexane,  322. 

Hexa-methylene-amme,  128. 

Hexa-methylene  carboxylic  acid,  443. 

Hexane,  30. 

Hexane-pentolal,  309. 


708 


INDEX 


Hexa-phenyl-ethane,  690. 
Hexoses,  300,  307  et  seg. 
Hexoses,  synthesis  of,  312,  319. 


Hexoses,  300,  307  et  seg. 

,  synthesis 
Hexyl  alcohol,  67. 


Hexylene,  43. 
Hippuric  acid,  211,  447. 
Histidine,  596,  599. 
Histories,  599. 

Hofmanris  reaction,  107,  369. 
Homatropine,  565. 
Homocatechol,  419. 
Homologous  series,  20. 
Homology,  20. 
Homo-phthalic  acid,  547. 
Homoterpenylic  methyl  ketone,  579. 
Honey-stone,  470. 
Hydantoic  acid,  285. 
Hydantoi'n,  285. 
Hydracryclic  acid,  216. 
Hydrastine,  563. 
Hydratropic  acid,  443,  454. 
Hydrazides,  398. 
Hydrazine,  212,  297. 
Hydrazines,  aromatic,  397. 
Hydrazines,  fatty,  109,  in. 
Hydrazo-benzene,  394,  396. 
Hydrazo-compounds,  395. 
Hydrazoic  acid,  212,  298. 
Hydrazones,  aromatic,  424,  428. 
Hydrazones,  carbohydrate,  301. 
Hydrazones,  fatty,  127,  135. 
Hydriodic  acid  as  a  reducing1  agent,  605. 
Hydro-benzoic  acids,  445. 
Hydro-benzoin,  478. 
Hydro-carbostynl,  454. 
Hydro-coumaric  acids,  459. 
Hydro-ferricyanic  acid,  271. 
Hydro-ferrocyanic  acid,  270. 
Hydro-isophthalic  acids,  469. 
Hydro-paracoumaric  acid,  459. 
Hydro-phthalic  acids,  466-469. 
Hydro-terephthalic  acids,  466. 
Hydrocarbons,  benzene,  344. 
Hydrocarbons,  fatty,  30. 
Hydrocinnamic  acid,  443,  453. 
Hydrocotarnine,  562,  563. 
Hydrocyanic  acid,  264,  266. 
Hydrocyanic  acid  derivatives,  100. 
Hydrocyano-carbpdiphenylimide,  524. 
Hydrogen,  detection  of,  3. 
Hydrogen,  estimation  of,  4.  [623. 

Hydrogen  peroxide  as  an  oxidizing  agent, 
Hydrolysis  =  Saponification,   70,   92,    159, 

176,  183. 

Hydrolysis  of  disaccharoses,  312. 
Hydrolysis  of  esters,  176. 
Hydrolysis    of   ethyl    acetoacetate,    226- 
Hydrolysis  of  nitriles,  101.  [227. 

Hydromellitic  acid,  470. 
Hydropyridines,  540. 
Hydroquinolines,  546. 
Hydroquinone  =  £?Mzw0/,  418. 
Hydroxy-acetic  acid,  209. 
Hydroxy-acetone,  204. 
Hydroxy-acids,   204  et  seg.,  247  et  seq., 

456  et  seq. 

Hydroxy  aldehydes,  204. 
Hydroxy-anthracenes,  508. 


Hydroxy-anthraquinones,  509. 
Hydroxy-azobenzene,  397. 
Hydroxy-benzaldehydes,  429. 
Ilydroxy-benzene,  411. 
Hydroxy-benzoic  acids,  443,  457  e 
Hydroxy-benzyl  alcohol,  429,  593. 
Hydroxy-butyric  acids,  207. 
Hydroxy-camphenilic  acid  lactone,  584. 
Hydroxy-caproic  acids,  216. 
Hydroxy-cmoromethyl  ether, 
Hydroxy-ethylamine,  189,  19 
Hydroxy-ethyl-sulphonic  aci 
Hydroxy-isobutyric  acid,  207. 
Hydroxy-ketones,  204. 
Hydroxy-malonic  acid,  247. 
Hydroxy-methyl-benzoic  acid,  46 
Hydroxy-phenyl-alanine,  459.' 


28. 


197. 


Hydroxy  -  phenylamino  -  propiomc 
Ilydroxy-pnenyl-ethyl  alcohol,  670. 
Hydroxy-phenyl-propionic  acid,  459. 
Hydroxy-propionic  acids,  207,  213. 
Hydroxy-pyndenes,  538. 
Hydroxy-quinaldine,  543. 
Hydroxy-quinol,  408,  420. 
Hydroxy-quinoline,  543,  546. 
Hydroxy-succinic  acid,  247. 
Hydroxy-terpane-one,  590. 
Hydroxy-thiotolene,  £20. 
Hydroxy-tricarballylic  acid,  262. 
Hydroxy-uracyl,  287. 
Hydroxyl  groups,  estimation  of,  201., 
Hydroxylamines,  in,  397,  609. 
Hydroxylenes,  351. 
Hyoscyamine,  566. 
Hypoxanthine,  293. 

/=  inactive,  249. 
Iditol,  307. 
Idonic  acid,  307. 
Idosaccharic  acid,  307. 
Idoses,  307. 
Imid-azole,  530. 
Imides,  239. 

Imido-carbonic  acid,  281. 
Imido-chlorides,  186. 
Imino-ethers,  185,  187,  447. 
Imino-formyl  chloride,  268. 
Imino  group,  104. 
Imino-thio-ethers,  186.  ,    T 

Indamines,  434. 
Indican,  526. 
Indigo,  525. 
Indigo-brown,  526. 
Indigo-carmine,  526. 
Indigo-purpurin,  528. 
Indigo-red,  526. 
Indigo-sulphonic  acids,  526. 
Indigo  syntheses,  526-527. 
Indigo-white,  526,  527. 
Indirubin,  528. 
Indol-alanine,  596. 
Indole,  520,  521,  525. 
Indophenin,  520. 
Indophenols,  434. 
Indoxyl,  522,  52^. 
Indoxyl-sulphunc  acid,  523, 
Indoxylic  acid,  523. 
Inosite,  421. 


[596. 
acid, 


INDEX 


709 


internal  viscosity,  665. 

Inulin,  319. 

Inversion,  315. 

Invert  sugar,  315. 

Invertase,  77,  318. 

lodoacetic  acid,  167. 

lodo-benzene,  354. 

lodo-propionic  acids,  167,  171 

lodoform,  56,  63. 

lodole,  518. 

lodonium  compounds,  360. 

lodopropanes,  60. 

lodoso-benzene,  359. 

lodoxy-benzene,  359. 

lonones,  589. 

Irene,  589. 

Iron  albuminate,  599. 

Iron  and  dilute  acid  as  reducing  agents, 

Iron  peptonate,  599.  [603. 

I  rone,  589. 

Isatic  acid,  463. 

I  satin,  457,  463,  523,  525. 

Isatin-anihde,  524. 

Isatin  chloride,  524. 

Isatin,  constitution  of,  525,  649. 

Isatin  ethers,  524. 

Isatogenic  acid,  524. 

Isethionic  acid,  197. 

Isoamygdalin,  592. 

Iso-amyl-iso-valerate,  178. 

Iso-barbituric  acid,  287. 

Iso-butane,  38. 

Isobutyl  alcohol,  67,  68. 

Isobutyl  carbinol,  80. 

Isobutyric  acid,  153. 

Iso-cinchomeronic  acid,  540. 

Iso-cinnamic  acids,  454. 

Iso-crotonic  acid,  164. 

Isocyanic  esters,  272. 

Isocyanides,  102. 

Isocyanuric  esters,  275. 

Isocyclic  compounds,  322. 

Iso-dialuric  acid,  288. 

Iso-durene,  345. 

Isodynamic  isomerism,  657. 

Iso-hydrobenzo'in,  478. 

Isomaltose,  316,  673. 

Iso-melamines,  277. 

Isomerism,  12,  87. 

Isomerism,  position,  133. 

Isomerism,  side-chain,  340. 


Isomerism,  stereo-chemical,  137,  154,  243, 

25°>  3°7.  3.2S'  341-  39°.  428>  627- 
Isomerism. in  the  cyanogen  group,   100- 


104,  273,  684. 
Isomerism  of  fumaric  and  maleic  acids, 
Isomerism  of  paraffins,  38.  [243. 

Isomerism  of  polymethylene  derivatives, 

32S- 
Isomerism  of  the  benzene  derivatives,  329 

et  seq. 

Isomers  of  the  diazo-compounds,  389. 
Iso-nicotinic  acid,  539. 
Iso-nitriles,  102,  371. 
Iso-nitro-methane,  96. 
Iso-nitroso-acetone,  136. 
Iso-nitroso-camphor,  586. 
Iso-nitroso-ketones,  136. 


Iso-paraffins,  32. 
Iso-phthalic  acid,  466. 
Isoprene,  567,  568. 
Isopropyl,  39. 
Isopropyl-acetic  acid,  153. 
Isopropyl  alcohol,  67,  70. 
Isopropyl-benzene,  353. 
Isopropyl  chloride,  60. 
Isopropyl  iodide,  60. 
Isopropyl-methyl-benzene,  352. 
Iso-quinoline,  541,  547. 
Iso-rhamnose,  307. 
Isorosindulines,  553. 
Iso-saccharic  acid,  260. 
Iso-stilbene,  478. 
Iso-succinic  acid,  241. 
Iso-thio  acid  amides,  186. 
Iso-thiocyanates,  276,  371. 
Iso-valeric  acid,  153. 
Isuret,  188. 

Japan  camphor,  585. 
uglone,  503. 
umper,  oil  of,  581. 

Keratin,  599. 
Ketens,  691. 
Keto-butyric  acid,  223. 
Keto-enolic  tautomensm,  227. 
Keto-hexoses,  311. 
Keto-ketens,  692. 
Ketone-aldehydes,  204, 
Ketones,  aliphatic,  131  et  seq.,  677, 
Ketones,  aromatic,  427. 
Ketones,  constitution  of,  132. 
Ketones,  mixed,  132. 
Ketonic  acids,  aromatic,  461. 
Ketonic  acids,  fatty,  204,  222,  259. 
Ketonic  acids,  fermentation  of,  670. 
Ketonic  hydrolysis,  226. 
Ketoses,  300,  303. 
Ketoximes,  aliphatic,  135,  137. 

/=lsevo-rotatory,  249. 

Lactalbumin,  599. 

Lactam  formation,  453. 

Lactamide,  215. 

Lactates,  215. 

/-Lactic  acid,  synthesis  of,  661. 

Lactic  acids,  168,  205,  213  et  seq,,  669. 

Lactic  acids,  derivatives  of,  215. 

Lactic  fermentation,  214, 

Lactide,  215. 

Lactim  formation,  453. 

Lacto-biose,  315. 

Lactones,  217. 

Lactose,  315. 

Lactyl  chloride,  215. 

Lactyl-urea,  285. 

Lactylic  acid  or  Lactic  anhydride,  215. 

Laevo-coniine,  557. 

Lffivo-limonene,  §75. 

Lasvo-tartaric  acid,  249. 

Laevulic  acid,  223,  230. 

Laevulose,  311. 

Lakes,  400,  509. 

Laudanosine,  561. 

Laurie  acid,  140,  157. 


710 


INDEX 


Lead,  sugar  of,  151. 

Lead,  tetraethyl,  120. 

Lead,  tetramethyl,  120. 

Lead,  trimethyl  hydroxide,  120. 

Lead  acetates,  151. 

Lead  mercaptan,  89. 

Lead  peroxide  as  an  oxidizing  agent,  622, 

Leather,  460. 

Le  Bel-van  t  ffoff  hypothesis,  154. 

Leucaniline,  484. 

Leucaurine,  490. 

Leucine,  216,  596,  669. 

Leuco-bases,  482. 

Leuco-compounds,  399,  482. 

Leuco-malachite  green,  483. 

Leuco-rosolic  acid,  490. 

Lichenin,  319. 

Ltebermanris  reaction,  377,  409. 

Light  blue,  489. 

Light  green,  489. 

Lignoceric  acid,  140. 

Ligroi'n,  42. 

Limonene  nitroso-chloride,  575,  578. 

Limonene  tetrabromide,  575,  578. 

Limonenes,  574,  575. 

Linalool,  572. 

Lipase,  668,  672. 

Liponic  acid,  559. 

Liver  starch,  319. 

Lotusin,  592. 

Lupetidines,  540. 

Luteolin,  541. 

Lutidines,  539. 

Lutidimc  acid,  540. 

Lysine,  219,  596. 

Lyxose,  306. 

Madder  root,  509. 

Magenta,  484,  487. 

Magnetic  susceptibility,  665. 

Malachite  green,  484. 

Malamic  acid,  248. 

Malamide,  248. 

Maleic  acid,  242. 

Malic  acid,  247. 

Malonic  acid,  231,  237,  241. 

Malonic  anhydride,  238. 

Malonic  ester,  237. 

Malonic  ester  synthesis,  237. 

"  Malonyl",  233. 

Malonyl-urea,  288. 

Malt  sugar,  315. 

Maltase,  78,  318,  671,  672. 

Maltobiose,  315. 

Maltose,  315,  673. 

Mandelic  acid,  443,  461. 

Manganese  dioxide  as  an  oxidizing  agent, 

Mannide,  203.  [623. 

Mannitan,  203. 

Mannitol,  203,  307. 

Manno-heptose,  660. 

Manno-nonose,  660. 

Manno-octose,  660. 

Manno-saccharic  acid,  260,  307. 

Mannonic  acid,  220,  307. 

Mannose-phenyl-hydrazone,  310. 

Mannoses,  307,  310. 

Margaric  acid,  140. 


Marsh  -gas,  34. 
Martins'  yellow,  502. 
Mauve,  552,  553. 
Meconme,  562. 
Melamine,  277. 
Melene,  43,  49. 
Melibiose,  316. 
Melissic  acid,  140. 
Melissic  alcohol,  81. 
Melissic  palmitate,  158,  178. 
Melitriose,  316. 
Mellitene,  353. 
Mellitic  acid,  34^,  470. 
Mellophanic  acid,  470. 
Melting-point,  25,  638. 
Melting-point  curves,  638. 
Melting-point    curves    of   racemic   com- 
pounds, 258. 

Mendius  reaction,  106,  606. 
Menthadienes,  574. 
Menthane,  574. 
Menthene,  578. 
Menthol,  578. 
Menthone,  578. 

Menthone-semicarbazone,  579. 
Menthyl  benzoyl-formate,  661. 
Menthyl  lactates,  660. 
Menthyl  phenyl-methyl-glycollate,  661. 
Menthyl  pyruvate,  660. 
Mercaptans,  88. 
Mercaptides,  88. 
Mercaptol,  136. 
Mercurialin,  no. 
Mercuric  cyanide,  269. 
Mercuric 'formate,  149. 
Mercuric  mercaptide,  89. 
Mercuric  oxide  as  an  oxidizing  agent,  626. 
Mercurous  formate,  149. 
Mercurous  thiocyanate,  276. 
Mercury  ethyl,  120. 
Mercury  fulminate,  688. 
Mercury  methyl,  120. 
Merpquinine,  559. 
Mesidme,  367. 
Mesityl  oxide,  135,  137. 
Mesitylene,-i3$.  339,  342,  345,  351. 
Mesitylenic  acid,  443,  453. 
Meso-tartaric  acid,  246,  249,  254. 
Mesoxalic  acid,  199,  260. 
Mesoxalyl-urea,  288. 
Meta-compounds,  333,  337. 
Metacymene,  345. 
Metaldehyde,  129. 
Metallic  cyanides,  268,  684-687. 
Metamerism,  87. 
Metanilic  acid,  406. 
Metaproteins,  600. 
Meta-styrene,  353. 
Methacrylic  acid,  165. 
Methanal,  128. 
Methane,  30,  34. 
Methane  acid,  147. 
Methane-amide,  185. 
Methanol,  74. 
Methene,  47. 

Methoxy-benzaldehyde,  429. 
Methoxy-benzyl  alcohol,  429. 
Methoxy-group,  177. 


INDEX 


711 


Methoxy-hydrqxy-benzaldehyde,  429. 
Methoxy-pyridine,  538. 
Methoxy-quinoline-carboxylic  acid,  559. 
Methyl-acetanilide,  382. 
Methyl-acridine,  548. 
Methyl  alcohol,  67,  74. 
Methyl-alloxan,  288. 
Methyl -allyl  -  phenyl  -benzyl  -ammonium 

iodide,  631. 
Methyl-amine,  no. 
Methyl-aniline,  367,  377. 
Methyl-arbutin,  593. 
Methyl-arsenic  compounds,  115  et  seq. 
Methyl-arsine  chlorides,  115  et  seq. 
Methyl-benzene;   see   Toluene,   340,   345, 
Methyl-benzimido-azole,  380.  [350. 

Methyl  benzoate,  445. 
Methyl-benzqic  acids,  443,  449,  452. 
Methyl  bromide,  56. 
2-Methyl-butane  acid,  154. 
3-Methyl-butane  acid,  153. 
Methyl  carbonate,  280. 
Methyl-carbqstyril,  543. 
Methyl  chloride,  56,  59. 
Methyl-chloroform,  63. 
Methyl-cyanamide,  278. 
Methyl-cyanide,  102. 
Methyl  dimethyl-amino-acetate,  212. 
Methyl  ether,  86. 
Methyl-ethyl-acetic  acid,  154. 
Methyl-ethyl-aceto-acetic  ester,  228. 
Methyl-ethyl-aniline  oxide,  633. 
Methyl-ethyl-benzenes,  345. 
Methyl-ethyl-carbinol,  126. 
Methyl-eth}'l  ether,  84. 
Methyl-ethyl  ketone,  i-;?.  [628. 

Methyl-cthyl-phenacyl-sulphine  bromide, 
Methyl-ethyl-propyl-iso-butyl-ammonium 

chloride,  632. 
Methyl-ethyi-w-propyl-tin  £?-camphor  sul- 

phonate,  629. 

Methyl-ethyl-propyl-tin  iodide,  629. 
Methyl-ethyl-selenetine  bromide,  628. 
Methyl-ethyl  sulphide,  89. 
Methyl-ethyl  sulphone,  89. 
Methyl-ethyl-thetine  bromide,  628. 
Methyl  -  ethyl  -  thetine       d-  camphor  -  sul  - 

phonate,  628. 
Methyl-furane,  517. 
Methyl  galactoside,  311. 
Methyl  glucosides,  310,  592,  672. 
Methyl-glycocoll,  212. 
Methyl-glyoxal,  204. 
Methyl-green,  480. 
Methyl-heptenone,  571. 
Methyl-hydantoin,  285. 
Methyl-hydrazine,  112. 
Methyl-indole,  521. 
Methyl  iodide,  56. 
Methyl-isatin,  524,  649. 
Methyl  isocyanide,  103. 
Methyl-isopropyl-benzene,  352. 
Methyl-isoprqpyl-hydroxy-benzenes,  417. 
Methyl-iso-thiacetanilide,  187. 
Methyl  isothiocyanate,  277. 
Methyl-malonic  acid,  233,  241. 
Methyl-morphmethine,  564. 
Methyl-morphol,  564. 


Methyl-naphthylamines,  500. 

Methyl-nitramine,  109. 

Methyl  nitrate,  93. 

Methyl  nitrite,  94. 

Methyl-nitrolic  acid,  96,  689. 

Methyl-orange,  401. 

Methyl  oxalate,  236. 

Methyl-oxamic  ester,  106. 

Methyl-parabanic  acid,  287. 

Methyl-phenyl-fr uctosazone,  311. 

Methyl-phosphonic  acid,  114. 

Methyl-piperidines,  540. 

Methyl-propane  acid,  153. 

Methyl-propane  di-acid,  241. 

2-Methyl-2-propene-i-acid,  165. 

Methyl-propyl-benzenes,  352. 

Methyl-pyridines,  538. 

Methyl-pyridone,  538. 

Methyl-pyridonium  iodide,  534. 

Methyl-pyrrolidine,  569. 

Methyl-quinolines,  543,  546. 

Methyl-succinic  acid,  "241. 

Methyl  sulphate,  98. 

Methyl-sulphonic  acid,  99. 

Methyl-tertiary-butyl  ketone,  137. 

Methyl-uracyl,  230,  287. 

Methyl-urea,  285. 

Methyl-uric  acids,  292. 

Methyl  violets,  488. 

Methyladipic  acid,  578. 

Methylal,  128. 

Methylamine  platinichloride,  107. 

Methylated  rosanilines,  488. 

Methylene,  47. 

Methylene  blue,  554. 

Methylene  bromide,  56,  61. 

Methylene  chloride,  56,  61. 

Methylene-glycol,  192. 

Methylene  iodide,  56,  61. 

Methylene-quinones,  434. 

Methylene  violet,  553. 

Micro-organisms   for   resolving  racemic 

compounds,  256. 
Milk  sugar,  315. 
Millon's  reagent,  594. 
Mineral  lubricating  oils,  42. 
Mint  camphor,  578. 
Miricyl  alcohol,  81. 
Mixed  amines,  106. 
Mixed  anhydrides,  181. 
Mixed  ethers,  84. 
Mixed  ketones,  132. 
Mixed  sulphides,  89. 
Molasses,  314. 

Molecular  magnetic  rotation,  644. 
Molecular  rearrangements,  108,  137,  163, 

377.  393.  395-  39?.  4".  5<>i- 
Molecular  refraction,  641. 
Molecular  rotation,  656. 
Molecular  volume,  639. 
Molecular  weight,  determination  of,  8-ia 
Monoformin,  148. 
Monohydric  alcohols,  65. 
Monohydroxy  fatty  acids,  205. 
Mononitrin,  200. 
Monopalmitin,  201. 
Monosaccharoses,  299. 
Mordants,  400. 


712 


INDEX 


Morphine,  564. 
Morpholine,  531. 
Moss  starch,  319. 
Mucic  acid,  259,  307. 
Mucins,  600. 
Multi-rotation,  309. 
Murexide,  289. 
Muscarine,  196. 
Musk,  artificial,  362. 
Mustard  oils,  275,  371". 
Mutarotation,  309,  315,  658. 
Myosin,  277,  599. 
Mynstic  acid,  140,  157. 
Myronic  acid,  593. 
Myrosin,  275,  593. 

Naphthalene,  471,  494. 
Naphthalene-carboxylic  acids,  504. 
Naphthalene-dicarboxylic  acids,  504. 
Naphthalene  dichloride,  497. 
Naphthalene-sulphonic  acids,  501. 
Naphthalene  tetrachloride,  497. 
Naphthalic  acid,  504. 
Naphthaquinones,  503. 
Naphthazarine,  503. 
Naphthazines,  550. 
Naphthenes,  41. 
Naphthionic  acid,  501. 
Naphtho-acridines,  548. 
Naphtho-phen-oxazine,  550. 
Naphthoic  acids,  503. 
Naphthol  dyes,  502. 
Naphthol-sulphonic  acids,  502. 
Naphthol  yellow,  502. 
Naphthols,  495,  501. 
Naphthylamine-sulphonic  acids,  501. 
Naphthylamines,  499. 
Narcotine,  561. 
Nerol,  572. 
Nerolin,  502. 
Neurine,  196. 
Neutral  esters,  91,  97. 
Neutral  red,  552. 
Neutral  violet,  552. 
Nicholson's  blue,  489. 
Nickel  powder  and  hydrogen  as  a  reduc- 
ing- agent,  610. 
Nicotine,  557. 

JJJf  °£.nic  acid'  539.  557- 

Nile  blue,  554. 

Nitracetanilides,  374. 

Nitramines,  109. 

Nitranilic  acid,-  433. 

Nitranilines,  375,  652. 

Nitric  acid,  constitution,  95. 

Nitric  acid  as  an  oxidizing  agent,  621. 

Nitriles,  aliphatic,  101. 

Nitriles,  aromatic,  438. 

Nitriles,  constitution  of,  103. 

Nitro-alizarin,  510. 

Nitro-benzaldehydes,  426,  521. 

Nitro-benzene,  360,  361. 

Nitro-benzene,  electrolytic   reduction  of, 

615. 

Nitro-benzene  as  an  oxidizing  agent,  626. 
Nitro-benzene-sulphonic  acids,  405. 
Nitro-benzoic  acids,  446,  449. 
Nitro-benzoyl-formic  acid,  462,  523. 


Nitro  -  benzyl  -  phenyl-nitrosamine,  reduc« 

tion  of,  604. 

Nitro-camphors,  587,  657. 
Nitro-cinnamenes,  362. 
Nitro-cinnamic  acid  dibromide,  453. 
Nitro-cinnamic  acids,  455. 
Nitro-decane,  95. 
Nitro-derivatives,  aliphatic,  94. 
Nitro-derivatives,  aromatic,  359. 
Nitro-dimethyl-aniline,  378. 
Nitro-diphenyl-amines,  377. 
Nitro-ethane,  94. 
Nitro-glycerine,  201. 
Nitro-guanidine,  297. 
Nitro-mesitylene,  360. 
Nitro-methane,  94. 
Nitro-naphthalenes,  499. 
Nitro-naphthols,  502. 
Nitro-naphthylamines,  500. 
Nitro-phenols,  414,  653. 
Nitro-phenols,  salts  of,  414,  653. 
Nitro-phenyl-acetic  acid,  524. 
Nitro-phenyl-acetylene,  363. 
Nitro-phenyl-glyoxylic  acid,  523. 
Nitro-phenyl-hydrazine,  399. 
Nitro-phenyl-lactyl-methyl  ketone,  527. 
Nitro-phenyl-propiolic  acid,  456,  524. 
Nitro-prussic  acid,  272. 
Nitro-styrenes,  362. 
Nitro- tartaric  acid,  253. 
Nitro-thiophene,  519. 
Nitro-toluenes,  360,  362. 
Nitro-uracyl,  287. 
Nitro-uracyl-carboxylic  acid;  287. 
Nitro-xylenes,  360. 
Nitroform,  97. 
Nitrogen,  detection  of,  3. 
Nitrogen,  estimation  ofT  5. 
Nitrogen,  quinquevalent,  105,  379,  631. 
Nitrogen  bases  of  the  alkyl  radicals,  104. 
Nitrogen  isomerism,  138,  428,  631. 
Nitrolamines,  573. 
Nitrolic  acids,  96. 
Nitrosamines,  108,  376. 
Nitrosamines  of  aromatic  bases,  376.' 
Nitrosates  of  terpenes,  573. 
Nitrosites  of  terpenes,  573. 
Nitroso-benzene,  365. 
Nitroso-chlorides  of  terpenes,  573. 
Nitroso-diethyl-aniline,  379. 
Njtroso-dimethyl-aniline,  378. 
Nitroso-indole,  521. 
Nitroso-indoxyl,  523. 
Nitroso-limonenes,  575. 
Nitroso-phenol,  378,  414,  432. 
Nitrous  acid,  constitution  of,  95. 
Nomenclature,  international,  40. 
Nomenclature  of  the  alcohols,  73. 
Nomenclature  of   the  hydrocarbons,   39 
Nonane,  30.  \et  seg. 

Nondecyhc  acid,  140. 
Nonoses,  300. 
Nonyl  alcohol,  67. 
Nonylene,  43. 
Nonylic  acid,  140. 
Normal  esters,  91,  97. 
Normal  salts,  144. 
Norpinic  acid,  583. 


INDEX 


713 


Nucleic  acid,  599. 
Nucleo-proteins,  599. 

o  =  ortho;  see  Ortho-compounds. 

Octa-acetyl  derivatives  of  sugars,  314. 

Octa-decyler.e,  43. 

Octane,  30. 

Octoses,  300. 

Octyl  alcohol,  67. 

Octylamine,  no, 

Octylene,  43. 

Octylic  acid ;  see  Caprylic  acid,  175. 

CEnanthol,  129. 

Oil  of  bitter  almonds,  266,  423. 

Oil  of  the  Dutch  chemists,  44. 

Oils,  ethereal,  567. 

Oils  and  fats,  158. 

Olefine  bond,  44. 

Olefines,  42. 

Olefines,  constitution  of,  46. 

Olefines,  formation  of,  45. 

Oleic  acid,  158,  161,  165. 

Oleic  series  of  acids,  162. 

Olein,  158. 

Olive  oil,  158. 

Open  chains,  20,  321. 

Opianic  acid,  562. 

Opium  bases,  560,  564. 

Optical  activity,  154,  656,  694. 

Optically  active  compounds,  their  pre- 
paration by  means  of  ferments,  256. 

Orange,  oil  of,  568. 

Orange  II,  502. 

Orcinol,  408,  419. 

Organo-magnesium  compounds,  121,  403. 

Organp-metallic  compounds,  1 18,  403. 

Ornithine,  219,  596. 

Ortho-acetic  ester,  197. 

Ortho-acids,  142. 

Ortho-acids,  derivatives  of,  178. 

Ortho-carbonic  ester,  202,  281; 

Ortho-compounds,  333;  337. 

Ortho-formic  acid,  197. 

Ortho-quinones,  430. 

Osazones,  222,  301. 

Osones,  304. 

Oxal-acetic  acid,  260,  670. 

Oxalic  acid,  204,  231,  234,  241. 

Oxalic  ester;  see  Ethyl  oxalate. 

Oxaluric  acid,  286,  287. 

"Oxalyl",  233. 

Oxalyl  chloride,  234. 

Oxalyl-urea ;    see  Parabanic  acid,    286, 

Oxamethane,  237.  [287. 

Oxamic  acid,  234,  236. 

Oxamide,  234,  236. 

Oxanilic  acid,  382. 

Oxanilide,  382. 

Oxazole,  530. 

Oxidases,  671. 

Oxidation,  616. 

Oxidation,  catalytic,  674. 

Oxidation,  effects  of  conditions  on,  617. 

Oxidation,  electrolytic,  626. 

Oxidation  with  acidified  permanganate, 
619.  [618. 

Oxidation  with  alkaline  permanganate, 

Oxidation  with  chromic  anhydride,  620. 


Oxidation  with  chromyl  chloride,  620. 

Oxidation  with  dichromate  and  acid,  620. 

Oxidation   with    neutral   permanganate, 

Oxidation  with  nitric  acid,  621.  [619. 

Oxidation  with  oxygen,  623. 

Oxidation  with  ozone,  624. 

Oxidation  with  peroxides,  622. 

Oxidation  with  sulphuric  acid,  622. 

Oximes,  127,  135,  137/301,  428. 

Oximide,  237. 

Oxindole,  452,  522,  525. 

Oxonium  salts,  532. 

Oxozonides,  624. 

Oxy-carbanil,  constitution  of,  650. 

Oxy-hasmoglobin,  600. 

Oxy-methylene-camphor,  655. 

Oxy-proline,  596. 

Oxy-purine,  293. 

Oxy-uvitic  acid,  230. 

Oxygen,  estimation  of,  6. 

Ozokerite,  42. 

Ozone  as  an  oxidizing  agent,  624. 

Ozonides,  624. 

/=para;  see  Para-compound& 

Palatin  black,  503. 

Palmitic  acid,  140,  157,  161. 

Palmitin,  158. 

Palmito-nitrile,  102. 

Papaveraldine,  560. 

Papaverine,  560. 

Papaveroline,  560. 

Para-aldehyde,  129. 

Para-anthracene,  507. 

Para-compounds,  333,  337. 

Para-cyanogen,  265. 

Para-formaldehyde,  128. 

Para-fuchsine,  486. 

Para-lactic  acid,  2i.<;. 

Para-leucaniline,  484,  485, 

Para-quinones,  430. 

Para-rosaniline,  485. 

Para-tartaric  acid;  see  Racemie  acid,  24^,. 

Parabanic -acid,  286,  287. 

Paraffin,  liquid,  42. 

Paraffin  wax,  42. 

Paraffins,  31. 

Paraffins,  constitution  of,  38. 

Paraffins,  formation  of,  33. 

Paraurazine,  284. 

Paroxazine,  549. 

Partial  valencies,  683. 

Partition  coefficient,  28.   ' 

Patent  blue,  480. 

Pelargonic  acid,  165. 

Penta-chlor-aniline,  374. 

Penta-decylene,  43. 

Penta-decylic  acid,  140. 

Penta-hydric  alcohols,  201,  202. 

Penta-hydroxy-flavone,  541. 

Penta-methylene,  322. 

Penta-methylene-diamine,  196,  535,  598. 

Penta-phenyl-ethane,  690. 

Penta-triacontane,  30. 

Pentacetyl-galactose,  311. 

Pentacetyl-glucose,  303,  309. 

Pentane  acid,  153.    . 

Pentane  di-acid,  240. 


714 

Pentanes,  30,  38. 
Pentanone  di-acid,  260. 
Pentoses,  300,  306. 
Peppermint,  oil  or,  570. 
Pepsin,  598. 
Peptones,  598,  600 
Per-acid  salts,  144. 
Perbenzoic  acid,  440, 
Perchlor-ether,  86. 

Perchloro-ethane,  64. 

"  Peri  "-position,  490- 

Perkins  synthesis,  425,  441- .  . 

Permanganate    as   an   oxidizing  ag_ent, 

Peronine,  564. 


INDEX 


A  „_ oxidizing  agents,  622. 

Perozonides,  624. 
Petroleum,  41. 
Petroleum  ether,  42. 
Phaseolunatin,  592. 
Phellandrene,  577-      .  Q 

Phellandrene  derivatives,  578. 
"Phenacetine",  415- 
Phenacyl  bromide,  427. 
Phenanthra-qumone,  512. 
Phenanthrene,  510. 
Phenanthrene-/3-carboxyhc  acid,  5" 
Phenanthrene  picrate,  511. 
Phenanthrene-qumol,  512 
Phenanthrol,  512. 
Phenates,  407. 
Phenazine,  549,  551- 
Phenetedines,  415- 
Phenetole,  412. 
Pheno-safranine,  552. 
Phenocoll,  415. 
Phenol,  406.  4««, 
Phenol,  esters  of,  407. 
Phenol,  ethers  of,  407.  . 

Phenol-methyl  ether;  vxAnisok,  407 
Phenol-phthaleln,  492. 
Phenol-phthaline,  40?. 
Phenol-sulphonic  acids,  416. 
Phenolic  acids,  aromatic,  457. 
Phenols,  407. 
Phenoxazine,  554. 
Phenoxides,  407. 
Phenthiazine,  550. 
Phenyl  acetate,  413. 
Phenyl-acetic  acid,  443,  45^- 
Phenyl-acetylene,  353. 
Phenyl-acridine,  548.  .,     ~ 

Phenyl-acridonium  hydroxide,  665. 

Phenyl-alanine,  453,  S9&.  67°-  .          .,., 
Phenyl-allyLdimethyl-ammonium  iodide, 

Phenyl-amine,  372. 
Phenyl-amino-acetic  acid,  452. 
Phenyl-amino-propionic  acids,  453,  59°- 

Phenyl-benzoic  acid,  477. 

Phenyl -benzyl -methyl -ethyl -ammonium 

iodide,  632. 

Phenyl-carbimide,  383. 
Phenyl-carbinol,  421. 
Phenyl-chlpracetic  acid,  452. 
a-Phenyl-cinnamo-nitrile,  267. 
Phenyl-cyanide  ;  see  Bcnzomtrile,  447- 
Phenyl-dibromo-propionic  acid,  454. 
Phenyl-dimethyl-pyrazolone,  230,  529. 


Phenyl  -  dipropyl  -  methyl  -  ar""-y:-"V 
Phenyl-disulphide,  413.  [iodide,  632. 

Phenyl  ether,  412. 
Phenyl-ethyl-alcohols,  422,  670. 
Phenyl-ethyl  ether,  412. 
Phenyl-ethylene,  353. 
Phenyl-glucosazone,  309. 
Phenyl-glycerol,  422. 
Phenyl-glycine,  383. 
Phenyl-glycocoll,  383,  527. 
Phenyl-glycocoll-o-carboxyhc  acid,  527. 
Phenyl-glycollic  acid,  460. 

Phenyl-glyoxylic  acid,  427,  462. 

Phenyl-hydrazme,  398. 

Phenyl-hydrazones,  127,  135,  424.  427.428. 

Phenyl  hydrogen  sulphate,  412. 

Phenyl-hydrosulphide,  413. 

Phenyl-hydroxylamine,  394,  397- 

Phenyl-hydroxy-propiomc  acid,  462. 

Phenyl-imi  no-butyric  acid,  383. 

Phenyl-iodide'dichloride,  358. 
Phenyl-isocrotonic  acid,  456,  490. 
Phenyl-isocyanate,  383. 
Phenyl-isothiocyanate,  383. 
Phenyl  magnesium  bromide,  403. 


fnenyi-meLu>i-cu.v»     • — ^~ 
Phenyl-methyl  hydrazme,  398. 
Phenyl-methyl  ketone,  427. 
Phenyl-methyl-pyrazolone,  230,  529- 
Phenyl-naphthalene,  504. 
Phenyl-naphthylammes,  500. 
Phenyl-nitramine,  389. 
Phenyl-nitro-methane,  363. 
Phenyl-phenazomum  chloride,  553. 
Pheriyl-phosphine,  403- 
Phenyl-phosphinic  acid,  403. 
Phenyl-propiolic  acid,  443,  4Sb- 

Phenyl-propionic  acids,  453. 

Phenyl  radical,  329. 

Phenyl  salicylate,  45»- 

Phenyl-salicylic  acid,  458. 

Phenyl  sulphide,  413- 

Phenyl-sulphonamic  acid,  405. 

Phenyl  sulphone,  413- 

Phenvl-^-tolyl-anti-ketoxime,  429. 

Phenyl-J-tolyl-syn-ketoxime,429. 

Phenylene  diammes,  380. 

Phloretic  acid,  593. 

Phloretin,  593. 

Phloridzin,  593- 

Phloroglucinol,  343-  **  42°-  593- 

Phloroglucinol-di-carboxyhc  ester,  441- 

PWorollucinol-hexa-methyl  ether  42C 

Phloroglucinol-mono-meth>-l  ether,  542, 

Phlorollucinol-trimethyl  ether,  420. 

Phloroglucinol-trioxime,  420. 

Phloxin,  493. 

Phorone,  135.  i37»  6l3- 

Phosgene,  280.      < 

Phosphenyl  chloride,  403. 

Phosphine,  548. 

Phosphine-oxides,  113. 

Phosphines,  113  et  seq. 

Phosphinic  acids,  114. 

Phosphino-benzene,  403. 


INDEX 


715 


Phospho-benzene,  403. 

Phospho-proteins,  599. 

Phosphonic  acids,  1 14. 

Phosphonium  bases,  113,  114. 

Phosphoric  esters,  too. 

Phosphorous  esters,  100. 

Phosphorus,  detection  of,  4. 

Phosphorus,  estimation  of,  6. 

Phosphorus  compounds,  aromatic,  402. 

Phthalei'ns,  491. 

Phthalic  acids,  464,  466. 

Phthalic  anhydride,  465. 

Phthalide,  462,  466. 

Phthalimide,  465. 

Phthalines,  492. 

Phthalo-phenone,  465,  491. 

Phthalyl  chloride,  465. 

Physical  properties  of  organic  compounds, 

Picene,  512.  [24  et  seq.,  635  et  seq. 

Picolines,  538. 

Picolinic  acid,  539. 

Picramide,  375. 

Picric  acid,  414. 

Picryl  chloride,  362,  415 

Pimaric  acid,  591. 

Pimelic  acid,  231,  344. 

Pinacoline,  137,  193. 

Pinacone,  193. 

Pinene,  581. 

Pinene  dibromide,  582. 

Pinene  glycol,  582. 

Pinene  hydrochloride,  582. 

Pinene  nitroso-chloride,  582. 

Pinic  acid,  583. 

Pinole,  582,. 

Pinonic  acid,  583. 

Pipecplines,  540. 

Piperic  acid,  464,  540. 

Piperidei'ns,  540. 

Piperidine,  196,  531,  534,  535,  540. 

Piperidme,  constitution  of,  535. 

Piperine,  464,  540. 

Piperonal,  429. 

Piperpnylic  acid,  460. 

Pivalic  acid,  157. 

Platinichlorides,  107,  370. 

Polyamines,  aromatic,  380. 

Polybasic  acids,  261. 

Polymerism,  12. 

Polymerization  of  acetylenes,  51,  341. 

Polymerization  of  aldehydes,  126. 

Polymerization  of  nitriles,  102. 

Polymerization  of  defines,  45. 

Polymethylene  derivatives,  322  et  seq. 

Polypeptides,  597,  600,  672. 

Polysaccharoses,  299,  316. 

Polyterpenes,  567. 

Ponceau,  2  R,  503. 

Populin,  593. 

Position  isomerism,  87. 

Potassium  acetates,  151. 

Potassium  antimonyl-tartrate,  253. 

Potassium  carboxide,  343. 

Potassium  cyanate,  273. 

Potassium  cyanide,  269. 

Potassium  diazobenzene  oxide,  390. 

Potassium  ethide,  119. 

Potassium  ethyl-carbonate,  280. 


Potassium  ferricyanide,  271. 

Potassium  ferricyanide  as  an  oxidizing1 
agent,  626. 

Potassium  ferri-ferrocyanide,  271. 

Potassium  ferrocyanide,  270. 

Potassium  ferro-ferrocyariide,  271. 

Potassium  formate,  148. 

Potassium  indoxyl-sulphate,  523. 

Potassium  methide,  119. 

Potassium  methoxide  =  potassium  methy- 

Potassium  myronate,  277.  [late,  75. 

Potassium  persulphate  as   an  oxidizing 

Potassium  pyrrole,  518.  [agent,  626. 

Potassium  thiocyanate,  275. 

Potassium  xanthate,  295. 

Prehnitic  acid,  470.  [146. 

Primary,  secondary,  and  tertiary  acids, 

Primary,  secondary,  and  tertiary  alcohols, 
68-70,  72,  97.  [104  et  seq. 

Primary,  secondary,  and  tertiary  amines, 

Primary,  secondary,  and  tertiary  di- 
amines,  195. 

Primary,  secondary,  and  tertiary  nitro- 
compounds,  96.  [phines,  113. 

Primary,  secondary,  and   tertiary  phos- 

Primary,  secondary,  tertiary,  and  qua- 
ternary hydrazines,  112. 

Prism  formula  of  benzene,  336. 

Proline,  596. 

Propadiene,  53. 

Propane,  30,  38. 

Propane  di-acid,  237. 

Propane-diol  acid,  218. 

Propanc-diols,  192. 

Propane-nitrile,  102. 

Propane-2-pl-i-acid,  214. 

Propane- tricarboxylic  acid,  261. 

Propane-triol,  198. 

Propanol,  80. 

Propanol  di-acid,  247. 

Propanone,  136. 

Propargyl  alcohol,  82. 

Propargylic  acid,  166. 

Propenal,  130. 

Propene,  48. 

Propene  acid,  164. 

Propine,  53. 

Propmol,  82. 

Propio-nitrile,  102. 

Propiolic  acid,  166. 

Propionic  acid,  140,  152, 

Propionyl,  14^7. 

Propyl  bromides,  56,  Co. 

Propyl  carbonate,  z''o. 

Propyl  chlorides,  56,  Co. 

Propyl  iodides,  56,  60. 

Propyl-acetic  acid,  153. 

Propyl-aceto-acetic  ester,  ziQ 

Propyl-alcohols,  67,  £o. 

Propyl- aldehyde,  129. 

Propyl-amines,  no. 

Propyl-benzenes,  345,  352. 

Propyl-methyl-benzenes,  352. 

Propyl-piperidincs,  538. 

Propyl-pseudo-nitrol,  96. 

Propyl-pyridines,  538. 

Propylene,  43,  48. 

Propylene  glycols,  192. 


716 


INDEX 


Protamines,  599. 

Proteins,  599. 

Proteoses,  600. 

Protocatechuic  acid,  459,  542. 

Protocatechuic  aldehyde,  429. 

Prussian  blues,  271. 

Prussic  acid,  266. 

Pseudo-acids,  96,  364,  491,  665. 

Pseudo-bases,  487. 

Pseudo-cumene,  345,  352. 

Pseudo-cumenol,  408. 

Pseudo-cumidine,  367. 

Pseudo-indoxyl.  523. 

Pseudo-methylisatin,  524. 

Pseudo-nitrols,  97. 

Pseudo-phenols,  434. 

Pseudo-uric  acid,  291. 

Ptoma'mes,  196,  598. 

Pulegone,  570,  579. 

Purine,  290. 

Purine  group,  290  et  sea. 

Purpuric  acid,  289.   . 

Purpurin,  510. 

Putrescine,  195,  598. 

Pyrazine,  531,  550. 

Pyrazole,  528,  695. 

Pyrazolidine,  528. 

Pyrazoline,  528,  695. 

Pyrazolone,  528. 

Pyrene,  512. 

Pyridazine,  531,  550. 

Pyridine,  322,  531,  533. 

Pyndine-carboxylic  acids,  539,  545,  560. 

Pyridine  derivatives,  536  et  scq. 

Pyridyl-methyl-pyrrole,  558. 

Pyridyl-methyl-pyrrolidine,  557. 

Pyridyl-pyrrole,  558. 

Pyrimidine,  531,  550. 

Pyro-mellitic  acid,  470. 

Pyro-mucic  acid,  518. 

Pyro-racemic  acid,  223,  225. 

Pyro-tartaric  acid,  241. 

Pyrocatechin  =  CafecAp/,  417. 

Pyrogallol  —  Pyrogallic  acid,  408,  419. 

Pyrogallol-carboxylic  acid,  460. 

Pyrogallol-dim,ethyl  ether,  420. 

Pyrohgneous  acid,  150. 

Pyrone,  531. 

Pyrone-dicarboxylic  acid,  533. 

Pyronine,  492,  547. 

Pyroxylme,  317. 

Pyrrole,  322,  515,  518. 

Pyrrolidine,  519. 

Pyrrolidine-carboxylic  acid,  596. 

Pyrroline,  518. 

Pyruvic  acid,  204,  225,  670. 

Pyruvic  acid  phenyl-hydrazone,  226. 

Qualitative  analysis,  2. 

Quantitative  analysis,  4. 

Quaternary  ammonium  bases,  104,  379. 

juercitin,  541. 

Juercitol,  421. 

Juinaldine,  543,  544,  546. 

Jumhydrpne,  431. 

)uinic  acid,  461,  559. 

nnine,  558. 

linitol,  419. 


>uinol,  408,  418. 
)uinol-dicarboxylic  acid,  469. 
Juinoline,  541,  542. 
)uinoline  carboxylic  acids,  546. 
Juinoline  decahydride,  546. 
Juinoline  yellow,  546. 
)uinolinic  acid,  536,  540. 
>uinolinium  salts,  546. 
juinone  chlorimide,  434. 
Juinone  dichlorimide,  434. 
Juinone-aniles,  434. 
Juinone-dioxime,  432. 
Juinone-oxime,  434. 
Juinones,  381,  430,  503,  508,  512,  652. 
Juinonoid  formulae,  486. 
>uinovose,  307. 
Quinoxaline,  551. 

Racemic  acid,  249,  253. 

Racemic  compounds,  253,  258. 

"Racemic"  modification,  156. 

Racemisation,  257,  629. 

Radicals,  22. 

Raflfinose,  316,  671. 

Red  prussiate  of  potash,  271. 

"Reduced"  benzene  derivatives,  348,  466 

Reduction,  601.  '[et  seq. 

Reduction,  catalytic,  610. 

Reduction,  electrolytic,  614. 

Reduction  in  acid  solution,  601. 

Reduction  in  alkaline  solution,  606. 

Reduction  in  neutral  solution,  608. 

Reduction  with  ethyl  alcohol,  609. 

Reduction  with  hydrogen  sulphide,  610. 

Reduction  with  metals,  609.  , 

Reduction  with  nascent  hydrogen,  601. 

Reduction  with  sodium  ethoxide,  609. 

Reduction  with  sodium  hyposulphite,  610 

Reduction  with  sodium  stannite,  609. 

Reduction  with  sulphurous  acid,  610. 

Reformatsky's  reaction,  263. 

Refraction,  molecular,  641,  693. 

Resin  acids,  591. 

Resin  soaps,  591. 

Resins,  591. 

Resolution  of  ^-lactic  acid,  215. 

Resolution  of  f-mandelic  acid,  462. 

Resolution  of  racemic  compounds,  253. 

Resorcin  yellow,  401. 

Resorcinol,  408,  418. 

Retene,  512. 

Rhamnazin,  541. 

Rhamnetin,  541. 

Rhamnitol,  203. 

Rhamnose,  306. 

Rhodamines,  493. 

Rhodeose,  307. 

Ribose,  306. 

Rochelle  salt,  253. 

Rosaniline,  485. 

Rosaniline  group,  484. 

Rosaniline  salts,  485. 

Rosinaulines,  553. 

Rosolic  acid,  490. 

Sabinene,  585. 
Saccharate,  strontium,  314. 
Saccharic  acid,  259,  307. 


INDEX 


717 


Saccharjmetry,  315. 

Saccharine,  452. 

Saccharo-biose,  314. 

Saccharomyces,  76,  80. 

Safranines,  552-553. 

Sage,  oil  of,  581. 

Salicin,  592. 

Salicyl-aldehyde,  429. 

Salicylic  acid,  443,  457. 

Saligenin,  429,  593. 

Salmine,  596. 

Salol,  458. 

Salophene,  458. 

Saloquinine,  560. 

Salt  out,  159,  594. 

Salts  or  fatty  acids,  144. 

Salts  of  sorrel,  236. 

Sandmeyer's  reaction,  388. 

Saponification,  70,  158. 

Sarcine,  293. 

Sarco-lactic  acid,  215. 

Sarcosine,  212. 

Saturated  hydrocarbons,  30. 

Saturation  isomerism,  133. 

Scarlet,  Biebrich,  503. 

Schiff's  bases,  371,  425. 

Schijfs  reagent,  488. 

Scleroproteins,  599. 

Secondary  alcohols,  69  et  seq.,  126. 

Secondary  arsines,  1 16. 

Secondary  butyl  iodide,  60. 

Secondary  nitro-compounds,  90. 

Seignette  salt,  253. 

Selenium  compounds,  91. 

Semicarbazide,  136. 

Semicarbazones,  136. 

Semicylic  bonds,  574,  694. 

Serine,  218,  596. 

Serum  albumin,  599. 

Sesqui-terpenes,  567. 

Shellac,  591. 

Side-chain  isomerism,  340. 

"Side  chains",  347. 

Silico-nonane,  1 18. 

Silico-nonyl  alcohol,  118. 

Silicon  compounds,  118,  629. 

Silk,  artificial,  318. 

Silver  formate,  149. 

Silver  fulminate,  688. 

Silver  oxide  as  an  oxidizing  agent,  626. 

Simple  ethers,  84. 

Simple  ketones,  132. 

Sinigrin,  593. 

Skatole,  522. 

Skatolglycocoll,  $96. 

Skraup's  synthesis,  542. 

Slow  neutralization,  665. 

Soaps,  158  et  seq. 

Sobrerol,  582. 

Sobrerythritol,  583. 

Sodio-aceto-acetic  ester,  228. 

Sodio-malonic  ester,  237. 

Sodium  acetate,  151.  [608. 

Sodium  amalgam  as  reducing  agent,  605, 

Sodium  as  a  reducing  agent,  606. 

Sodium  ethide,  1 19. 

Sodium  ethoxide,  79. 

Sodium  formate,  147. 


Sodium  glycolls,  191. 

Sodium  methide,  119. 

Sodium  nitro-prusside,  270. 

Solanine  bases,  565. 

Solubility,  24. 

Soluble  starch,  319. 

Sorbic  acid,  166,  682. 

Sorbitols,  203,  307. 

Sorbose,  312. 

Sozo-iodol,  414. 

Sozolic  acid,  416. 

Specific  gravity,  25,  639. 

Specific  refractive  power,  641. 

Specific  rotatory  power,  656. 

Specific  volume,  25. 

Spermaceti,  158. 

Spirit  blue,  489. 

Spirits  of  wine,  75.  [322. 

Stability  of   polymethylene   derivatives, 

Stannous  chloride  as  reducing  agent,  603. 

Starch,  319. 

Starch,  animal,  319. 

Starch,  soluble,  319. 

Steam  distillation,  27. 

Stearic  acid,  140,  157,  161,  198. 

Stearin,  158. 

Stearin  candles,  158. 

Stereochemistry  of  carbon,  154,  250,  307, 

325,  340,  634. 

Stereochemistry  of  cobalt,  634. 
Stereochemistry  of  nitrogen,  138,  428,  631. 
Stereochemistry  of  phosphorus,  634. 
Stereochemistry  of  selenion,  628. 
Stereochemistry  of  silicon,  629. 

Stereochemistry  of  sulphur,  628. 

Stereochemistry  of  tin,  629. 

Stereoisomerism,  154.  [340. 

Stereoisomerism  of  benzene  derivatives, 

Stereoisomerism  of  glucoses,  &c.,  307. 

Stereoisomerism  of  oximes,  138,  428,  635. 

Stereoisomerism  of  polymethylene  deriva- 
tives, 325. 

Stereoisomerism  of  tartaric  acids,  250. 

Stereoisomerism  of  valeric  acids,  &c.,  154. 

Steric  retardation  or  hindrance,  175,  449, 

Stilbene,  471,  478.  [651. 

Stilbene  dibromide,  478. 

Storax,  353,  423,  454. 

Strychnine,  565. 

Strychnine  bases,  565. 

Sturine,  599. 

Styphnic  acid,  418. 

Styrene,  353. 

Suberic  acid,  231. 

"Substantive  dyes",  473,  478. 

Substituted  benzoic  acids,  448. 

Substitution,  31,  55. 

Substitution,  inverse,  45. 

Substitution,  laws  governing,  448. 

Succinamic  acid,  239. 

Succinamide,  239. 

Succinic  acid,  231,  238,  241,  669,  670, 

Succinic  anhydride,  240. 

Succinimide,  234,  239. 

Succinpnitrile,  194. 

"Succinyl",  233. 

Succinyl  chloride,  240. 

Succinylosuccinic  acid,  469. 


718 


INDEX 


Sucrase,  671. 

Sucrose,  314. 

Sugars,  the,  300  et  seq. 

Sulphanilic  acid,  405. 

Sulphides,  88,  90. 

Sulphinic  acids,  aromatic,  405. 

Sulphinic  acids,  fatty,  99. 

Sulpho-acetic  acid,  171. 

Sulpho-benzimide,  452. 

Sulpho-benzoic  acids,  452. 

Sulpho-urea,  296. 

Sulphobenzylethylpropylsilicyl  oxide,  630. 

Sulphonal,  136. 

Sulphones,  89,  90. 

Sulphonic  acids,  aliphatic,  99. 

Sulphonic  acids,  aromatic,  403. 

Sulphonium  salts,  90. 

Sulphoxides,  89,  90. 

Sulphur,  detection  of,  3. 

Sulphur,  estimation  of7  6. 

Sulphur,  valency  of,  90. 

Sulphuric  acid  as  an  oxidizing-  agent,  622. 

"  Sulphuric  ether",  85. 

Sylvane,  517. 

Sylvestrene,  576. 

Sylvestrene  derivatives,  578. 

5y?i-aldoximes,  139. 

Syn-d'iazo  compounds,  391. 

Synthetic  enzymes,  673. 

Synthetical  terpenes,  576,  578,  580. 

Syringin,  593. 

Tagatose,  312. 

Talitols,  307. 

Talo-mucic  acid,  260,  307. 

Talonic  acid,  307. 

Taloses,  307,  311. 

Tannic  acids,  460. 

Tannin,  460. 

Tar,  coal,  340. 

Tartar  emetic,  253. 

Tartaric  acid,  249  et  seq. 

Tartaric  acid,  esters  of,  253. 

Tartaric    acids,    inactive,    246,    249,    343. 

See  also  Dextro-,  Lcevo-,   and   Parct- 

tartaric  acids. 

Tartaric  acids,  stereoisomerism  of  the, 
Tartrates,  233.  [250. 

Tartronic  acid,  199,  247. 
Tartronyl  urea,  288. 
Taurine,  196. 

Taurochohc  acid,  196,  668. 
Tautomerism,  184,  227,  278,  420,  643,  649, 
Tellurium  compounds,  91.  [650. 

Terebenthene,  582. 
Terephthalic  acid,  466. 
Terpadieneone,  579. 
Terpadienes,  574. 
Terpadiol,  580. 
Terpane,  574. 
Terpanol,  578,  579. 
lerpanone,  578. 
Terpeneone,  579. 
Terpenes,  567  et  seq. 
Terpenylic  acid,  579. 
Terpin,  580. 
Terpin  hydrate,  581. 
Terpinene,  572. 


Terpinene  derivatives,  578. 
Terpineol,  576,  579,  583. 
Terpmolene,  576. 
Terpinolene  tetrabromide,  578. 
Tertiary  alcohols,  70  et  seq. 
Tertiary-butyl  iodide,  60. 
Tertiary  nitro-compounds,  96. 
Tervalent  carbon,  690. 
Tetra-acet-hydrazide,  185. 
Tetra-bromo-fluorescei'n,  493. 
Tetra-bromo-methane,  56. 
Tetra-chloro-aniline,  374. 
Tetra-chloro-methane,  56,  64. 
Tetra-chloro-quinone,  432. 
Tetra-decane,  30. 
Tetra-decylcne,  43. 
Tetra-ethyl-rhpdamine,  493. 
Tetra-ethyl-silicane,  118. 
Tetra-ethyl-tetrazone,  112. 
Tetra-hydro-benzene,  349. 
Tetra-hydro-benzoic  acids,  445. 
Tetra-hydro-naphthalene,  497. 
Tetra-hydro-naphthols,  502,  607. 
Tetra-hydro-naphthylamines,  500,  607. 
Tetra-hydro-phthalic  acids,  466. 
Tetra-hydro-pyridine,  540. 
Tetra-hydro-quinoline,  534,  546. 
Tetra-hydro-quinone,  432. 
Tetra-hydro-terephthahc  acids,  466,  468. 
Tetra-hydro-xylenes,  351. 
Tetra-hydroxy-anthra-quinone,  510. 
Tetra-iodo-pyrrole,  518. 
Tetra-methyl-ammonium  compounds,  1 1 
Tetra-methyl-benzenes,  345,  352. 
Tetra-methyl-diamino-tnphenyl-c,arbino 

483-  [48; 

Tetra-methyl-diammo-triphenyl-methani 
Tetra-methyl-ethylene  glycol,  193. 
Tetra  -  methyl  -  phosphomum     hydroxidi 
Tetra-methyl-silicane,  118.  [n, 

Tctra-methyl-stibonium  hydroxide,  118. 
Tetra-methylene,  322. 
Tetra-methylene-diamine,  195,  598. 
Tetra-methylene-dicarboxylic  acids,  325 
Tetra-methylene-imine,  519. 
Tetra-nitro-methane,  97. 
Tetra-phenyl-methane,  493. 
Tetra-phenyl-pyrazine,  551. 
Tetra-phenyl  thiopene,  519. 
Tetracetylene-dicarboxylic  acid,  247. 
Tetraethyl-phosphonium  hydroxide,  114 
Tetrahydric  alcohols,  201,  202. 
Tetrazole,  530. 
Tetrolic  acid,  166. 
Tetroses,  300. 
Thebaine,  564. 
Theine,  293. 
Theobromme,  293. 
Theophylline,  .293. 
Theory  of  valency,  13. 
Thiacetamide,  186. 
•Thiacetic  acid,  181. 
Thiamides,  186. 
Thiazines,  549. 
Thiazole,  529. 
Thio-acetamlide,  382. 
Thio-acids,  181. 
Thio-alcohols,  87. 


INDEX 


719 


Thio-benzamide,  447. 

Thio-carbamic  compounds,  296. 

Thio-carbamide,  296. 

Thio-carbanilide,  524. 

Thio-carbonic  acids,  295. 

Thio-carbonic  compounds,  295. 

Thio-carbonyl  chloride,  295. 

Thio-cyanates,  275  et  seq. 

Thio-cyanic  acid,  275. 

Thio-cyanic  ester,  275. 

Thio-ethers,  87. 

Thio-glycols,  191. 

Thio-phenol,  413. 

Thio-phosgene,  295. 

Thio-urea,  278,  296. 

Thiols,  88,  677. 

Thionessal,  519. 

Thiophene,  322,  350,  515,  519. 

Thiophene-carboxylic  acid,  520. 

Thiophene-sulphonic  acid,  520. 

Thiotolene,  520. 

Thujenes,  585. 

Thyme,  oil  of,  568. 

Thymo-quinone,  433. 

Thymol,  408,  417,  579. 

Tiemann-Reimer  reaction,  409,  430,  440. 

Tiglic  acid,  161,  165. 

Tin,  alkyl  compounds  of,  120. 

Tin  and  hydrochloric  acid  as   reducing 

agents,  602. 
Tolane,  478. 
Tolidine,  474. 
Tolu-quinone,  433. 
Toluene,  340,  345,  350. 
Toluene-sulphonic  acids,  406. 
Toluic  acids,  443,  452. 
Toluidides,  382. 
Toluidines,  367,  375. 
Toluylene  blue,  552. 
Toluylene  red,  552. 
Tolyl  alcohols,  422. 
Tolyl-acetic  acids,  443. 
Tolyl-diphenyl-methanes,  482. 
Tolyl-phenyl-methanes,  476. 
Toxines,  icJ6,  598. 
"Trans"  form,  246,  326. 
Transition  temperatures,  255. 
Tri-acetone  peroxide,  181. 
Tri-amines,  aromatic,  381. 
Tri-amino-azobenzene  nydrochloride,  401. 
Tri-amino-diphenyl-tolyl-methane,  484. 
Tri-amino-triphenyl-carbinol,  485. 
Tri-amino-triphenyl-methane,  484. 
Tri-azo  compounds,  695. 
Tri-azole,  530. 
Tri-bromacetic  acid,  167. 
Tri-bromaniline,  374. 
Tri-bromo-phenol,  414. 
Tri-carballylic  acid,  261. 
Tri-chloraniline,  373. 
Tri-chlorhydrin,  200. 
Tri-chloro-acetal,  130. 
Tri-chloro-acetic  acid,  167,  170. 
Tri-chloro-aldehyde  =  Chloral,  129. 
Tri-chloro-benzenes,  357. 
Tri-chloro-cyanogen,  272. 
Tri  chloro-ethanal,  129. 
Tri-chloro-methane,  63. 


Trj-chloro-phenomalic  acid,  343. 

Tri-chloro-propane,  200. 

Tri-chloro-purine,  290. 

Tri-cosane,  30. 

Tri-decylene,  43. 

Tri-decylic  acid,  140. 

Tri-diphenyl-methyl,  691. 

Tri-ethylamine,  in. 

Tri-ethyl-arsine,  116. 

Tri-ethyl-benzene,  342. 

Tri-ethyl-phosphine,  114. 

Tri-hydric  alcohols,  197. 

Tri-hydric  phenols,  419. 

Tri-hydrocyanic  acid,  269. 

Tri-hydroxy-anthraquinones,  510, 

Tri-hydroxy-benzenes,  419. 

Tri-hydroxy-benzoic  acids,  460. 

Tri-hydroxy-glutaric  acids,  259. 

Tri-hydroxy-purine,  290,  291. 

Tri-hydroxy-terpane,  579. 

Tri-keto-hexamethylene,  420. 

Tri-mellitic  acid,  470. 

Tri-methyl-acetic  acid,  157. 

Tri-methyl-arsine,  116,  117. 

Tri-methyl-arsine  dichloride,  117. 

Tri-methyl-arsine  oxide,  117. 

Tri-methyl-benzenes,  345,  351. 

Tri  -  methyl  -  carballylic  acid  =  Campho- 
ronic  acid,  586. 

Tri-methyl-carbinol,  73. 

Tri-methyl-glycocoll  =  Beta'ine,  212. 

Tri-methyl-hydroxyethyl-ammonium  hy- 
droxide —  Choline,  196.  [379. 

Tri-methyl-phenyl-ammonium  hydroxide, 

Tri-methyl-phosphine  oxide,  1 14. 

Tri-methyl  -  pyndine  -  dicarboxylic  ester, 

Tri-methyl-pyridines=  Collidines,  539. 
Tri-methyl-stibine,  117. 
Tri-methyl-succinic  acid,  586. 
Tri-m ethyl- sulphine  hydroxide,  90. 
Tri-methyl-sulphine  iodide,  90. 
Tri-methyl-sulphonium  hydroxide,  90. 
Tri-methyl-sulphonium  iodide,  90. 
Tri-methyl  -  vinyl  -  ammonium  hydroxide, 
Tri-methyl-xanthine,  293.  [196. 

Tri-methylamine,  no. 
Tri-methylamine  oxide,  in. 
Tri-methylene,  322. 
Tri-methylene  bromide,  192. 
Tri-methylene  glycol,  192. 
Tri*nitrin,  201. 

Tri-nitro-benzene,  362.  [ride,  362. 

Tri-nitro-chloro-benzene  =  Picryl  chlo- 
Tri-nitro-naphthalene,  499. 
Tri-nitro-phenol ;  see  Picric  acid,  414. 
Tri-nitro-tertiary-butyl-toluene,  362. 
Tri-nitro-triphenyl-carbinol,  481. 
Tri-nitro-triphenyl-methane,  481. 
Tri-olei'n ;  see  Olein,  165. 
Tri-oxy-methylene,  128. 
Tri-palmitin,  201. 
Tri-phenylamine,  379. 
Tri-phenyl-benzene,  474. 
Tri-phenyl-carbinol,  422,  481. 
Tri-phenyl-carbinol-o-carboxylic  acid,  491 
Tri-phenyl-fuchsine,  489. 
Tri-phenyl-methane,  471,  481. 


720 


INDEX 


Tri-phenyl-methanc-carboxylic  acid,  491. 

Tri-phenyl-methane  dyes,  482. 

Tri-phenyl-methyl,  690. 

Tri-phenyl-methyl  bromide,  481. 

Tri-phenyl-methyl  peroxide,  690. 

Tri-saccharoses,  299. 

Tri-stearin,  201. 

Tri-thio-carbonic  acid,  295. 

Trimesic  acid,  470. 

Trimesic  ester,  342. 

Triple  bond,  49. 

Trisaccharoses,  299,  300,  305,  312. 

Tropaeoline  O,  402. 

Tropaeolines,  401. 

Tropei'nes,  565. 

Tropic  acid,  443,  462,  565. 

Tropidine,  566. 

Tropine,  565. 

Tropine-carboxylic  acid,  566. 

Tropinic  acid,  566. 

Trypsin,  598. 

Tryptophan,  596. 

Turnbull's  blue,  271. 

Turpentine,  oil  of,  581. 

Types,  theory  of,  13-15. 

Tyrosine,  459,  596,  670. 

Tyrosol,  670. 

Umbellic  acid,  464. 
Umbelliferone,  464. 
Undecane,  30. 
Undecylene,  43. 
Undecyljc  acid,  140. 
Unorganized  ferments ;  see  Enzymes. 
Unsaturated  acids,  161,  434,  679. 
Unsaturated  alcohols,  81,  422. 
Unsaturated  dibasic  acids,  241. 
Unsaturated  hydrocarbons,  42,  353. 
Unsaturated  monobasic  acids,  161. 
Unsaturation,  types  of,  678. 
Unsaturation    and    physical    properties, 


Urea,  acyl  derivatives  of,  285. 
Urea,  alkyl  derivatives  of,  284. 
Urea,  determination  of,  283. 
Urea,  salts,  &c.,  of,  283. 
Urea  =  Carbamide,  i,  281,  282. 
Ureides,  285,  286  et  seq. 
Ureido-acids,  286  et  seq. 
Urethanes,  282. 
Uric  acid,  290,  291. 
Uric  acid,  derivatives  of,  294. 
Uvitic  acid,  466. 

Valency,  theory  of,  13,  683. 
Valency  of  sulphur,  90. 
Valeric  acids,  140,  153. 
Valero-lactpne,  530. 
Valero-nitrile,  102. 
Valerone,  i-i-j. 
Valine,  596. 
Vanillic  acid,  459. 
Vanillic  alcohol,  429 
Vanillin,  430,  593. 


[693- 


Vapour  density,  determination  of,  9 

Vapour  pressure,  lowering'  of,  12. 

Vaseline,  42. 

Veratric  acid,  460, 

Victoria  green,  484. 

Victoria  orange,  417. 

Vinegar,  150. 

Vinyl  acetic  acid,  165. 

Vinyl  alcohol,  81. 

Vinyl  bromide,  56,  65. 

Vinyl  chloride,  56. 

Vinyl  iodide,  56. 

Vinyl-ethyl  ether,  87. 

Violuric  acid,  288. 

Viscoid,  318. 

Viscose,  318. 

Viscosity,  665. 

Walden  inversion,  661. 
Wandering  of  groups,  395. 
Water  blue,  489. 
Wax  varieties,  158. 
Williamson  s  blue,  271. 
Wine,  78. 

Wine,  spirits  of,  75. 
Wintergreen,  oil  of,  74,  457. 
Wood  gum,  306. 
Wood  spirit,  74. 
Wood  sugar,  306. 
Wood  tar,  74. 

Xanthjc  acid,  296. 
Xanthine,  292,  599. 
Xantho-cheudonic  acid,  533. 
Xantho-protei'n  reaction,  the,  594.   . 
Xanthone,  549. 
Xylene-carboxylic  acids,  453. 
Xylene-sulphonic  acids,  406. 
Xylenes,  345,  351. 
Xylenols,  408. 
Xylidides,  382. 
Xylidines,  367. 
Xylitol,  203. 
Xylo-quinone,  342, 
Xylose,  306. 

Yeast,  76,  666. 

Yeast  juice,  667. 

Yellow  prussiate  ot  potash,  270. 

Zinc  and  acid  as  reducing  agents,  60^ 

et  seq. 

Zinc  and  alcohol  as  reducing  agents,  608. 
Zinc  and  alkali  as  reducing  agents,  608. 
Zinc  dust  and   acetic  acid   as   reducing 

Zinc  dust  and  saline  solutions  as  reducing 

Zinc  ethyl,  120.  [agents,  609. 

Zinc  methide,  119. 

Zinc  methoxide,  120. 

Zinc-methyl  iodide,  120. 

Zymase,  77,  304,  667, 

Zymin,  667. 


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rB  16754 


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UNIVERSITY  OF  CALIFORNIA  LIBRARY 


